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Sleep deprivation (SD) is a recognized risk factor for atrial fibrillation (AF), yet the precise molecular and electrophysiological mechanisms behind SD-induced AF are unclear. This study explores the electrical and structural changes that contribute to AF in chronic partial SD. We induced chronic partial SD in Wistar rats using a modified multiple-platform method. Echocardiography demonstrated impaired systolic and diastolic function in the left ventricle (LV) of the SD rats. The SD rats exhibited an elevated heart rate and a higher low-frequency to high-frequency ratio in a heart-rate variability analysis. Rapid transesophageal atrial pacing led to a higher incidence of AF and longer mean AF durations in the SD rats. Conventional microelectrode recordings showed accelerated pulmonary vein (PV) spontaneous activity in SD rats, along with a heightened occurrence of delayed after-depolarizations in the PV and left atrium (LA) induced by tachypacing and isoproterenol. A Western blot analysis showed reduced expression of G protein-coupled receptor kinase 2 (GRK2) in the LA of the SD rats. Chronic partial SD impairs LV function, promotes AF genesis, and increases PV and LA arrhythmogenesis, potentially attributed to sympathetic overactivity and reduced GRK2 expression. Targeting GRK2 signaling may offer promising therapeutic avenues for managing chronic partial SD-induced AF. Future investigations are mandatory to investigate the dose-response relationship between SD and AF genesis.

Glucagon-like peptide-1 (GLP-1) receptor agonists are associated with reduced atrial fibrillation risk, but the mechanisms underlying this association remain unclear. The GLP-1 receptor agonist directly impacts cardiac Ca 2+ homeostasis, which is crucial in pulmonary vein (PV, the initiator of atrial fibrillation) arrhythmogenesis. This study investigated the effects of the GLP-1 receptor agonist on PV electrophysiology and Ca 2+ homeostasis and elucidated the potential underlying mechanisms. Conventional microelectrodes and whole-cell patch clamp techniques were employed in rabbit PV tissues and single PV cardiomyocytes before and after GLP-1 (7-36) amide, a GLP-1 receptor agonist. Evaluations were conducted both with and without pretreatment with H89 (10 μM, an inhibitor of protein kinase A, PKA), KN93 (1 μM, an inhibitor of Ca 2+ /calmodulin-dependent protein kinase II, CaMKII), and KB-R7943 (10 μM, an inhibitor of Na + /Ca 2+ exchanger, NCX). Results showed that GLP-1 (7-36) amide (at concentrations of 1, 10, and 100 nM) reduced PV spontaneous activity in a concentration-dependent manner without affecting sinoatrial node electrical activity. In single-cell experiments, GLP-1 (7-36) amide (at 10 nM) reduced L-type Ca 2+ current, NCX current, and late Na + current in PV cardiomyocytes without altering Na + current. Additionally, GLP-1 (7-36) amide (at 10 nM) increased sarcoplasmic reticulum Ca 2+ content in PV cardiomyocytes. Furthermore, the antiarrhythmic effects of GLP-1 (7-36) amide on PV automaticity were diminished when pretreated with H89, KN93, or KB-R7943. This suggests that the GLP-1 receptor agonist may exert its antiarrhythmic potential by regulating PKA, CaMKII, and NCX activity, as well as modulating intracellular Ca 2+ homeostasis, thereby reducing PV arrhythmogenesis.

Aims: Macrophage migration inhibitory factor (MIF), a pleiotropic inflammatory cytokine, is highly expressed in patients with atrial fibrillation (AF). Inflammation increases the risk of AF and is primarily triggered by pulmonary vein (PV) arrhythmogenesis. This study investigated whether MIF can modulate the electrical activity of the PV and examined the underlying mechanisms of MIF., Methods and Results: A conventional microelectrode, a whole-cell patch clamp, western blotting, and immunofluorescent confocal microscopy were used to investigate electrical activity, calcium (Ca2+) regulation, protein expression, ionic currents, and cytosolic reactive oxygen species (ROS) in rabbit PV tissue and isolated single cardiomyocytes with and without MIF incubation (100 ng/mL, treated for 6 h). The MIF (100 ng/mL)-treated PV tissue (n = 8) demonstrated a faster beating rate (1.8 ± 0.2 vs. 2.6 ± 0.1 Hz, P < 0.05), higher incidence of triggered activity (12.5 vs. 100%, P < 0.05), and premature atrial beat (0 vs. 100%, P < 0.05) than the control PV tissue (n = 8). Compared with the control PV cardiomyocytes, MIF-treated single PV cardiomyocytes had larger Ca2+ transients (0.6 ± 0.1 vs. 1.0 ± 0.1, ΔF/F0, P < 0.05), sarcoplasmic reticulum Ca2+ content (0.9 ± 0.20 vs. 1.7 ± 0.3 mM of cytosol, P < 0.05), and cytosolic ROS (146.8 ± 5.3 vs. 163.7 ± 3.8, ΔF/F0, P < 0.05). Moreover, MIF-treated PV cardiomyocytes exhibited larger late sodium currents (INa-Late), L-type Ca2+ currents, and Na+/Ca2+ exchanger currents than the control PV cardiomyocytes. KN93 [a selective calcium/calmodulin-dependent protein kinase II (CaMKII) blocker, 1 μM], ranolazine (an INa-Late inhibitor, 10 μM), and N-(mercaptopropionyl) glycine (ROS inhibitor, 10 mM) reduced the beating rates and the incidence of triggered activity and premature captures in the MIF-treated PV tissue., Conclusion: Macrophage migration inhibitory factor increased PV arrhythmogenesis through Na+ and Ca2+ dysregulation through the ROS activation of CaMKII signalling, which may contribute to the genesis of AF during inflammation. Anti-CaMKII treatment may reverse PV arrhythmogenesis. Our results clearly reveal a key link between MIF and AF and offer a viable therapeutic target for AF treatment., Competing Interests: Conflict of interest: None declared., (© The Author(s) 2022. Published by Oxford University Press on behalf of the European Society of Cardiology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Adrenomedullin, a peptide with vasodilatory, natriuretic, and diuretic effects, may be a novel agent for treating heart failure. Heart failure is associated with an increased risk of atrial fibrillation (AF), but the effects of adrenomedullin on atrial arrhythmogenesis remain unclear. This study investigated whether adrenomedullin modulates the electrophysiology of the atria (AF substrate) or pulmonary vein (PV; AF trigger) arrhythmogenesis. Conventional microelectrode or whole-cell patch clamps were used to study the effects of adrenomedullin (10, 30, and 100 pg/mL) on the electrical activity, mechanical response, and ionic currents of isolated rabbit PV and sinoatrial node tissue preparations and single PV cardiomyocytes. At 30 and 100 pg/mL, adrenomedullin significantly reduced the spontaneous beating rate of the PVs from 2.0 ± 0.4 to 1.3 ± 0.5 and 1.1 ± 0.5 Hz (reductions of 32.9% ± 7.1% and 44.9 ± 8.4%), respectively, and reduced PV diastolic tension by 12.8% ± 4.1% and 14.5% ± 4.1%, respectively. By contrast, adrenomedullin did not affect sinoatrial node beating. In the presence of L-NAME (a nitric oxide synthesis inhibitor, 100 μM), adrenomedullin (30 pg/mL) did not affect the spontaneous beating rate or diastolic tension of the PVs. In the single-cell experiments, adrenomedullin (30 pg/mL) significantly reduced the L-type calcium current (I Ca-L ) and reverse-mode current of the sodium-calcium exchanger (NCX). Adrenomedullin reduces spontaneous PV activity and PV diastolic tension by reducing I Ca-L and NCX current and thus may be useful for treating atrial tachyarrhythmia.

Background: Ceramide is involved in regulating metabolism and energy expenditure, and its abnormal myocardial accumulation may contribute to heart injury or lipotoxic cardiomyopathy. Whether ceramide can modulate the electrophysiology of pulmonary veins (PVs) remains unknown., Materials and Methods: We used conventional microelectrodes to measure the electrical activity of isolated rabbit PV tissue preparations before and after treatment with various concentrations of ceramide with or without H 2 O 2 (2 mM), MitoQ, wortmannin or 740 YP. A whole-cell patch clamp and fluorescence imaging were used to record the ionic currents, calcium (Ca 2+ ) transients, and intracellular reactive oxygen species (ROS) and sodium (Na + ) in isolated single PV cardiomyocytes before and after ceramide (1 μM) treatment., Results: Ceramide (0.1, 0.3, 1 and 3 μM) reduced the beating rate of PV tissues. Furthermore, ceramide (1 μM) suppressed the 2 mM H 2 O 2 -induced faster PV beating rate, triggered activities and burst firings, which were further reduced by MitoQ. In the presence of wortmannin, ceramide did not change the PV beating rate. The H 2 O 2 -induced faster PV beating rate could be counteracted by MitoQ or wortmannin with no additive effect from the ceramide. Ceramide inhibited pPI3K. Ceramide reduced Ca 2+ transients, sarcoplasmic reticulum Ca 2+ contents, L-type Ca 2+ currents, Na + currents, late Na + currents, Na + -hydrogen exchange currents, and intracellular ROS and Na + in PV cardiomyocytes, but did not change Na + -Ca 2+ exchange currents., Conclusion: C2 ceramide may exert the distinctive electrophysiological effect of modulating PV activities, which may be affected by PI3K pathway-mediated oxidative stress, and might play a role in the pathogenesis of PV arrhythmogenesis., (© 2021 Stichting European Society for Clinical Investigation Journal Foundation. Published by John Wiley & Sons Ltd.)

Atrial fibrillation (AF) is a common form of arrhythmia with serious public health impacts, but its underlying mechanisms are not yet fully understood. Vascular endothelial growth factor (VEGF) is highly expressed in the atrium of patients with AF, but whether VEGF affects AF pathogenesis remains unclear. Pulmonary veins (PVs) are important sources for the genesis of atrial tachycardia or AF. Therefore, this study assessed the effects of VEGF on PV electrophysiological properties and evaluated its underlying mechanisms. Conventional microelectrodes and whole-cell patch clamps were performed using isolated rabbit PV preparations or single isolated PV cardiomyocytes before and after VEGF or VEGF receptor (VEGFR), Akt, NOS inhibitor administration. We found that VEGF (0.1, 1, and 10 ng/mL) reduced the PV beating rate in a dose-dependent manner. Furthermore, VEGF (10 ng/mL) reduced late diastolic depolarization and diastolic tension. Isoproterenol increased PV beating and burst firing, which was attenuated by VEGF (1 ng/mL). In the presence of VEGFR-1 inhibition (ZM306416 at 10 μM) and L-NAME (100 μM), VEGF (1 ng/mL) did not alter PV spontaneous activity. In isolated PV cardiomyocytes, VEGF (1 ng/mL) decreased L-type calcium, sodium/calcium exchanger, and late sodium currents. In conclusion, we found that VEGF reduces PV arrhythmogenesis by modulating sodium/calcium homeostasis through VEGFR-1/NOS signaling pathway., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Introduction: Phosphodiesterase (PDE) isoform inhibitors have mechanical and electrical effects on the heart. Inhibition of PDE-1 enzymes is a novel strategy for treating heart failure. However, the electrophysiological effects of PDE-1 inhibition on the heart remain unclear. This study explored the effects of PDE-1 inhibition using ITI-214 on electrical activity in the pulmonary vein (PV), the most common trigger of atrial fibrillation, and investigated the underlying ionic mechanisms., Methods: Conventional microelectrodes or whole-cell patch clamps were employed to study the effects of ITI-214 (0.1-10 μM) on PV electrical activity, mechanical responses and ionic currents in isolated rabbit PV tissue specimens and isolated single PV cardiomyocytes., Results: ITI-214 at 1 μM and 10 μM (but not 0.1 μM) significantly reduced PV spontaneous beating rate (10 ± 2% and 10 ± 3%, respectively) and PV diastolic tension (11 ± 3% and 17 ± 3%, respectively). ITI-24 (1 μM) significantly reduced late sodium current (I Na-Late ), L-type calcium current (I Ca-L ) and the reverse mode of the sodium-calcium exchanger (NCX), but it did not affect peak sodium currents., Conclusions: ITI-214 reduces PV spontaneous activity and PV diastolic tension by reducing I Na-Late , I Ca-L and NCX current. Considering its therapeutic potential in heart failure, targeting PDE-1 inhibition may provide a novel strategy for managing atrial arrhythmogenesis., (© 2021 Stichting European Society for Clinical Investigation Journal Foundation. Published by John Wiley & Sons Ltd.)

Aims: Klotho, a potential antiageing protein has remarkable cardiovascular effects, which is lower in the patients with chronic kidney disease (CKD). Chronic kidney disease increases the risk of atrial fibrillation, majorly triggered by pulmonary vein (PV) arrhythmogenesis. This study investigated whether klotho protein can modulate PV electrical activity and the underlying potential mechanisms., Methods and Results: A conventional microelectrode and whole-cell patch clamp were used to investigate the action potentials and ionic currents in isolated rabbit PV tissue preparations and single cardiomyocytes before and after klotho administration. Phosphoinositide 3-kinase (PI3K)/Akt signalling was studied using western blotting. Klotho significantly reduced PV spontaneous beating rates in PV tissue preparations at 1.0 and 3.0 ng/mL (but not at 0.1 and 0.3 ng/mL). In the presence of the Akt inhibitor (10 µM), klotho (1.0 and 3.0 ng/mL) did not change PV electrical activities. Klotho (1.0 ng/mL) significantly decreased the late sodium current (INa-Late) and L-type calcium current (ICa-L), similar to the Akt inhibitor (10 µM). Western blots demonstrated that klotho (1.0 ng/mL)-treated PV cardiomyocytes had less phosphorylation of Akt (Ser473) compared with klotho-untreated cardiomyocytes. Compared with control PVs, klotho at relatively lower concentrations (0.1 and 0.3 ng/mL) significantly reduced beating rates and decreased the amplitudes of delay afterdepolarizations in CKD PVs., Conclusion: Klotho modulated PV electrical activity by inhibiting PI3K/Akt signalling, which may provide a novel insight into CKD-induced arrhythmogenesis., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2020. For permissions, please email: journals.permissions@oup.com.)

Atrial fibrillation (AF) is the most common form of arrhythmia and increases the risk of stroke and heart failure (HF). Pulmonary veins (PVs) are important sources of triggers that generate AF, and calcium (Ca 2+ ) overload participates in PV arrhythmogenesis. Neurohormonal activation is an important cause of AF. Higher atrial natriuretic peptide (ANP) level predicts paroxysmal AF occurrence in HF patients. However, it is not clear if ANP directly modulates electrophysiological characteristics and Ca 2+ homeostasis in the PVs. Conventional microelectrodes, whole-cell patch-clamp, and the Fluo-3 fluorimetric ratio technique were performed using isolated rabbit PV preparations or single isolated PV cardiomyocytes before and after ANP administration. We found that ANP (1, 10, and 100 nmol/L) concentration-dependently decreased spontaneous activity in PV preparations. ANP (100 nmol/L) decreased isoproterenol (1 μmol/L)-induced PV spontaneous activity and burst firing. AP811 (100 nmol/L, NPR-C agonist), H89 (1μmol/L, PKA inhibitor) decreased isoproterenol-induced PV spontaneous activity or burst firing, but successive administration of ANP had no further effect on PV activity. KT5823 (1 μmol/L, PKG inhibitor) decreased isoproterenol-induced PV spontaneous activity but did not change isoproterenol-induced PV burst firing, whereas successive administration of ANP did not change isoproterenol-induced PV burst firing. ANP decreased intracellular Ca 2+ transient and sarcoplasmic reticulum Ca 2+ content in single PV cardiomyocytes. ANP decreased the late sodium current, L-type Ca 2+ current, but did not change nickel-sensitive Na + -Ca 2+ exchanger current in single PV cardiomyocytes. In conclusion, ANP directly regulates PV electrophysiological characteristics and Ca 2+ homeostasis and attenuates isoproterenol-induced arrhythmogenesis through NPR-C/cAMP/PKA signal pathway., (© 2019 John Wiley & Sons Australia, Ltd.)

Background: Atrial fibrillation (AF) frequently coexists with congestive heart failure (HF) and arginine vasopressin (AVP) V1 receptor antagonists are used to treat hyponatremia in HF. However, the role of AVP in HF-induced AF still remains unclear. Pulmonary veins (PVs) are central in the genesis of AF. The purpose of this study was to determine if AVP is directly involved in the regulation of PV electrophysiological properties and calcium (Ca 2+ ) homeostasis as well as the identification of the underlying mechanisms., Methods: Patch clamp, confocal microscopy with Fluo-3 fluorescence, and Western blot analyses were used to evaluate the electrophysiological characteristics, Ca 2+ homeostasis, and Ca 2+ regulatory proteins in isolated rabbit single PV cardiomyocytes incubated with and without AVP (1 μM), OPC 21268 (0.1 μM, AVP V1 antagonist), or OPC 41061 (10 nM, AVP V2 antagonist) for 4-6 h., Results: AVP (0.1 and 1 μM)-treated PV cardiomyocytes had a faster beating rate (108 to 152%) than the control cells. AVP (1 μM) treated PV cardiomyocytes had higher late sodium (Na + ) and Na + /Ca 2+ exchanger (NCX) currents than control PV cardiomyocytes. AVP (1 μM) treated PV cardiomyocytes had smaller Ca 2+ i transients, and sarcoplasmic reticulum (SR) Ca 2+ content as well as higher Ca 2+ leak. However, combined AVP (1 μM) and OPC 21268 (0.1 μM) treated PV cardiomyocytes had a slower PV beating rate, larger Ca 2+ i transients and SR Ca 2+ content, smaller late Na + and NCX currents than AVP (1 μM)-treated PV cardiomyocytes. Western blot experiments showed that AVP (1 μM) treated PV cardiomyocytes had higher expression of NCX and p-CaMKII, and a higher ratio of p-CaMKII/CaMKII., Conclusions: AVP increases PV arrhythmogenesis with dysregulated Ca 2+ homeostasis through vasopressin V1 signaling.

Heart failure (HF) frequently coexists with atrial fibrillation (AF) and dysfunction of the sinoatrial node (SAN), the natural pacemaker. HF is associated with chronic adrenergic stimulation, neurohormonal activation, abnormal intracellular calcium handling, elevated cardiac filling pressure and atrial stretch, and fibrosis. Pulmonary veins (PVs), which are the points of onset of ectopic electrical activity, are the most crucial AF triggers. A crosstalk between the SAN and PVs determines PV arrhythmogenesis. HF has different effects on SAN and PV electrophysiological characteristics, which critically modulate the development of AF and sick sinus syndrome. This review provides updates to improve our current understanding of the effects of HF in the electrical activity of the SAN and PVs as well as therapeutic implications for AF.

Background: Ivabradine increases the risk of atrial fibrillation (AF). Heart failure (HF) or sinoatrial node (SAN) dysfunction increases the risk of AF, and pulmonary veins (PVs) play a critical role in the pathophysiology of AF. This study investigated the electrophysiologic effects of ivabradine on SANs and PVs in a rabbit model of HF., Methods and Results: Conventional microelectrodes were used to simultaneously record the electrical activities and conduction properties of control and HF rabbit SAN-PV preparations before and after perfusion with ivabradine (0.1, 1, or 10 μmol/L), either alone or with isoproterenol (1 μmol/L). HF SANs exhibited a lower beating rate than the control SANs. SAN automaticity exit blocks and SAN-PV conduction blocks were observed in 25% and 50% of samples, respectively, with P < .05 for HF SANs (n = 8) but not for control SANs (n = 6). Delayed afterdepolarization (DAD) was observed in 37.5% of HF PVs but not in control PVs. HF PVs exhibited a faster beating rate and more severe fibrosis than control PVs. Ivabradine reduced the SAN beating rates and increased the occurrences of SAN-PV conduction blocks and PV DADs in control and HF preparations. However, ivabradine induced SAN automaticity exit blocks only in HF preparations. Isoproterenol induced PV burst firing and shifting electrical conduction in control and HF preparations. A combination of isoproterenol and ivabradine (10 μmol/L) in HF preparations resulted in the highest incidences of PV burst firing and SAN-PV electrical shifting., Conclusions: HF differentially modulates the effects of ivabradine on the electrical activities of SAN and PVs, which may increase PV arrhythmogenesis and contribute to the risk of AF in HF patients., (Copyright © 2018. Published by Elsevier Inc.)

Factor Xa inhibitors reduce stroke in patients with atrial fibrillation. Pulmonary veins (PVs) and the sinoatrial node (SAN) are crucial for genesis of atrial fibrillation. However, the electrophysiological effects of factor Xa inhibitors (edoxaban and rivaroxaban) on PVs and the SAN remain unclear. Conventional microelectrodes were used to record the action potential in isolated rabbit PVs and SAN preparations before and after administration of edoxaban (0.1, 0.3, and 1 μM) or rivaroxaban (0.01, 0.03, 0.1, and 0.3 μM). A whole-cell patch-clamp was used to record the late sodium current (I Na-late ) in isolated single rabbit PV cardiomyocytes. Edoxaban significantly reduced PV spontaneous beating rates at 0.3 and 1 μM (N = 6 rabbits, P < 0.05), and reduced SAN beating rates at 1 μM (N = 6, P < 0.05). Similarly, rivaroxaban reduced PV spontaneous beating rates at 0.1 and 0.3 μM (N = 7, P < 0.05), and reduced SAN beating rates at 0.3 μM (N = 6, P < 0.05). However, neither edoxaban (1 μM) nor rivaroxaban (0.3 μM) reduced PV spontaneous beating rates in the presence of 1 μM BMS200261 (an inhibitor of protease-activated receptors type 1, PAR1 inhibitor) or 10 μM ranolazine (an inhibitor of late sodium current, I Na-late inhibitor). Edoxaban (0.3 and 1 μM) and rivaroxaban (0.1 and 0.3 μM) respectively decreased the I Na-late by 47%, 47%, 36%, and 49% (n = 9 PV cardiomyocytes from 5 rabbits, P < 0.05). In conclusion, Factor Xa inhibitors reduce PV spontaneous activities and may modulate occurrence of atrial fibrillation by inhibiting PAR1 and reducing the I Na-late in PVs., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Introduction: Calcium overload increases the risk of atrial fibrillation (AF). Levosimendan, a calcium sensitizer, increases myofilament contractility. Clinical reports suggested that levosimendan might increase AF occurrence, but the electrophysiological effects of levosimendan on AF substrates and triggers (pulmonary veins, PVs) are not clear., Methods and Results: Conventional microelectrodes were used to record action potentials (APs) in isolated rabbit PVs, sinoatrial nodes (SANs), the left atrium (LA), and right atrium (RA) before and after application of different concentrations of levosimendan with or without milrinone (a phosphodiesterase [PDE] III inhibitor), and glibenclamide (an ATP-sensitive potassium channel [K ATP ] inhibitor). Levosimendan (0.03, 0.1, 0.3, and 1 μM) significantly increased spontaneous rates from 2.1 ± 0.2 to 2.5 ± 0.2, 2.5 ± 0.2, 2.5 ± 0.1, and 2.7 ± 0.2 Hz, respectively, in PVs (n = 10), but had no effects on denudated PVs (n = 9). Additionally, levosimendan significantly induced burst firing and/or triggered beats in intact PVs, but not in denudated PVs. In contrast, levosimendan at 0.3 and 1 μM increased the SAN spontaneous rate. In the presence of milrinone (10 μM), levosimendan (1 μM) did not increase the PV spontaneous activity. Moreover, glibenclamide (100 μM) prevented acceleration of the levosimendan-induced SAN and PV rates. In the LA, levosimendan at 0.3 and 1 μM shortened the AP duration, and increased contractility at 0.03, 0.1, 0.3, and 1 μM. In contrast, levosimendan did not change the RA contractility, and shortened the AP duration only at 1 μM., Conclusions: Levosimendan increased PV arrhythmogenesis through activating endothelial PDE III and the K ATP , and modulating PV tension., (© 2018 Wiley Periodicals, Inc.)

Hydrogen sulphide (H 2 S), one of the most common toxic air pollutants, is an important aetiology of atrial fibrillation (AF). Pulmonary veins (PVs) and left atrium (LA) are the most important AF trigger and substrate. We investigated whether H 2 S may modulate the arrhythmogenesis of PVs and atria. Conventional microelectrodes and whole-cell patch clamp were performed in rabbit PV, sinoatrial node (SAN) or atrial cardiomyocytes before and after the perfusion of NaHS with or without chelerythrine (a selective PKC inhibitor), rottlerin (a specific PKC δ inhibitor) or KB-R7943 (a NCX inhibitor). NaHS reduced spontaneous beating rates, but increased the occurrences of delayed afterdepolarizations and burst firing in PVs and SANs. NaHS (100 μmol/L) increased I KATP and I NCX in PV and LA cardiomyocytes, which were attenuated by chelerythrine (3 μmol/L). Chelerythrine, rottlerin (10 μmol/L) or KB-R7943 (10 μmol/L) attenuated the arrhythmogenic effects of NaHS on PVs or SANs. NaHS shortened the action potential duration in LA, but not in right atrium or in the presence of chelerythrine. NaHS increased PKC activity, but did not translocate PKC isoforms α, ε to membrane in LA. In conclusion, through protein kinase C signalling, H 2 S increases PV and atrial arrhythmogenesis, which may contribute to air pollution-induced AF., (© 2018 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.)

Background: Atrial fibrillation (AF) is the most common sustained arrhythmia, and pulmonary veins (PVs) play a critical role in triggering AF. Angiotensin (Ang)-(1-7) regulates calcium (Ca 2+ ) homoeostasis and also plays a critical role in cardiovascular pathophysiology. However, the role of Ang-(1-7) in PV arrhythmogenesis remains unclear., Materials and Methods: Conventional microelectrodes, whole-cell patch-clamp and the fluo-3 fluorimetric ratio technique were used to record ionic currents and intracellular Ca 2+ in isolated rabbit PV preparations and in single isolated PV cardiomyocytes, before and after administration of Ang-(1-7)., Results: Ang (1-7) concentration dependently (0.1, 1, 10 and 100 nmol/L) decreased PV spontaneous electrical activity. Ang-(1-7) (100 nmol/L) decreased the late sodium (Na + ), L-type Ca 2+ and Na + -Ca 2+ exchanger currents, but did not affect the voltage-dependent Na + current in PV cardiomyocytes. In addition, Ang-(1-7) decreased intracellular Ca 2+ transient and sarcoplasmic reticulum Ca 2+ content in PV cardiomyocytes. A779 (a Mas receptor blocker, 3 μmol/L), L-NAME (a NO synthesis inhibitor, 100 μmol/L) or wortmannin (a specific PI3K inhibitor, 10 nmol/L) attenuated the effects of Ang-(1-7) (100 nmol/L) on PV spontaneous electric activity., Conclusion: Ang-(1-7) regulates PV electrophysiological characteristics and Ca 2+ homoeostasis via Mas/PI3K/eNOS signalling pathway., (© 2017 Stichting European Society for Clinical Investigation Journal Foundation.)

Background: Chronic kidney disease (CKD) increases the occurrence of atrial fibrillation and pulmonary vein (PV) arrhythmogenesis. Calcium dysregulation and reactive oxygen species (ROS) enhance PV arrhythmogenic activity. The purposes of this study were to investigate whether CKD modulates PV electrical activity through dysregulation of calcium homeostasis and ROS., Methods and Results: Biochemical and electrocardiographic studies were conducted in rabbits with and without CKD (induced by 150 mg/kg per day neomycin sulfate and 500 mg/kg per day cefazolin). Confocal microscopy with fluorescence and a whole-cell patch clamp were applied to study calcium homeostasis and electrical activities in control and CKD isolated single PV cardiomyocytes with or without treatment with H89 (1 μmol/L, a protein kinase A inhibitor) and MPG (N-[2-mercaptopropionyl]glycine; 100 μmol/L, a ROS scavenger). The ROS in mitochondria and cytosol were evaluated via intracellular dye fluorescence and lipid peroxidation. CKD rabbits had excessive atrial premature captures over those of control rabbits. Compared with the control, CKD PV cardiomyocytes had a faster beating rate and larger calcium transient amplitudes, sarcoplasmic reticulum calcium contents, sodium/calcium exchanger currents, and late sodium currents but smaller L-type calcium current densities. CKD PV cardiomyocytes had a higher frequency and longer duration of calcium sparks and more ROS in the mitochondria and cytosol than did controls. Moreover, H89 suppressed all calcium sparks in CKD PV cardiomyocytes, and H89- and MPG-treated CKD PV cardiomyocytes had similar calcium transients compared with control PV cardiomyocytes., Conclusions: CKD increases PV arrhythmogenesis with enhanced calcium-handling abnormalities through activation of protein kinase A and ROS., (© 2017 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley.)

Background: Heart failure (HF) plays a critical role in the genesis of atrial fibrillation (AF). A high B-type natriuretic peptide (BNP) level occurs in patients with HF and in patients with AF. However, the role of BNP in the pathophysiology of AF is not clear. The purposes of this study were to evaluate the effects of BNP on pulmonary vein (PV) arrhythmogenesis., Methods and Results: Whole-cell patch clamp and fluorescence were used to study the action potential, ionic currents, and calcium homeostasis in isolated single rabbit PV cardiomyocytes before and after a BNP infusion, with or without ODQ (10 μM), milrinone (50 μM), or ouabain (1 μM). BNP increased PV spontaneous activity by 28.2 ± 7.5% at 100 nM and by 23.8 ± 9.1% at 300 nM. Similar to those with BNP, milrinone 50 μM increased the PV beating rate from 3.0 ± 0.2 to 3.6 ± 0.3 Hz (P < 0.0005, n = 7). In the presence of ODQ application, BNP didn't change PV spontaneous activity. BNP (100 nM) increased calcium transients (F/F 0 from 1.6 ± 0.1 to 1.9 ± 0.2, n = 20, P < 0.05) and increased the pacemaker current (0.4 ± 0.1 to 1.0 ± 0.2 pA/pF, n = 17, P < 0.0005) in PV cardiomyocytes. Moreover, BNP (100 nM) increased the transient inward current, sodium currents, sodium-calcium exchanger currents, and L-type calcium current; but reduced late sodium currents and the Na-K pump in PV cardiomyocytes., Conclusion: BNP increases PV arrhythmogenesis, which may contribute to the genesis of atrial tachyarrhythmogenesis in HF. Cyclic GMP activation, phosphodiesterase 3 inhibition and Na + /K + -ATPase inhibition might participate in the BNP modulation of PV electrophysiology., (© 2016 Wiley Periodicals, Inc.)

AF (atrial fibrillation) is the most common sustained arrhythmia, and the PVs (pulmonary veins) play a critical role in triggering AF. Stretch causes structural remodelling, including cytoskeleton rearrangement, which may play a role in the genesis of AF. Lat-B (latrunculin B), an inhibitor of actin polymerization, is involved in Ca(2+) regulation. However, it is unclear whether Lat-B directly modulates the electrophysiological characteristics and Ca(2+) homoeostasis of the PVs. Conventional microelectrodes, whole-cell patch-clamp, and the fluo-3 fluorimetric ratio technique were used to record ionic currents and intracellular Ca(2+) within isolated rabbit PV preparations, or within isolated single PV cardiomyocytes, before and after administration of Lat-B (100 nM). Langendorff-perfused rabbit hearts were exposed to acute and continuous atrial stretch, and we studied PV electrical activity. Lat-B (100 nM) decreased the spontaneous electrical activity by 16±4% in PV preparations. Lat-B (100 nM) decreased the late Na(+) current, L-type Ca(2+) current, Na(+)/Ca(2+) exchanger current, and stretch-activated BKCa current, but did not affect the Na(+) current in PV cardiomyocytes. Lat-B reduced the transient outward K(+) current and ultra-rapid delayed rectifier K(+) current, but increased the delayed rectifier K(+) current in isolated PV cardiomyocytes. In addition, Lat-B (100 nM) decreased intracellular Ca(2+) transient and sarcoplasmic reticulum Ca(2+) content in PV cardiomyocytes. Moreover, Lat-B attenuated stretch-induced increased spontaneous electrical activity and trigger activity. The effects of Lat-B on the PV spontaneous electrical activity were attenuated in the presence of Y-27632 [10 μM, a ROCK (Rho-associated kinase) inhibitor] and cytochalasin D (10 μM, an actin polymerization inhibitor). In conclusion, Lat-B regulates PV electrophysiological characteristics and attenuates stretch-induced arrhythmogenesis., (© 2016 Authors; published by Portland Press Limited.)

Background: Hypokalemia and hyponatremia increase the occurrence of atrial fibrillation. Sinoatrial nodes (SANs) and pulmonary veins (PVs) play a critical role in the pathophysiology of atrial fibrillation., Objective: The purpose of this study was to evaluate whether electrolyte disturbances with low concentrations of potassium ([K(+)]) or sodium ([Na(+)]) modulate SAN and PV electrical activity and arrhythmogenesis, and to investigate potential underlying mechanisms., Methods: Conventional microelectrodes were used to record electrical activity in rabbit SAN and PV tissue preparations before and after perfusion with different low [K(+)] or [Na(+)], interacting with the Na(+)-Ca(2+) exchanger inhibitor KB-R7943 (10 μΜ)., Results: Low [K(+)] (3.5, 3, 2.5, and 2 mM) decreased beating rates in PV cardiomyocytes with genesis of delayed afterdepolarizations (DADs), burst firing, and increased diastolic tension. Low [K(+)] (3.5, 3, 2.5, and 2 mM) also decreased SAN beating rates, with genesis of DADs. Low [Na(+)] increased PV diastolic tension, DADs, and burst firing, which was attenuated in the co-superfusion with low [K(+)] (2 mM). In contrast, low [Na(+)] had little effect on SAN electrical activities. KB-R7943 (10 μΜ) reduced the occurrences of low [K(+)] (2 mM)- or low [Na(+)] (110 mM)-induced DAD and burst firing in both PVs and SANs., Conclusion: Low [K(+)] and low [Na(+)] differentially modulate SAN and PV electrical properties. Low [K(+)]- or low [Na(+)]-induced slowing of SAN beating rate and genesis of PV burst firing may contribute to the high occurrence of atrial fibrillation during hypokalemia or hyponatremia., (Copyright © 2016 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Renal failure (RF) increases the risk of atrial fibrillation (AF), but arrhythmogenic mechanism is unclear. The present study investigated the electrophysiological effects of RF on AF trigger (pulmonary veins, PVs) and substrate (atria) and evaluated potential underlying mechanisms., Methods: Electrocardiographic, echocardiographic, and biochemical studies were conducted in rabbits with and without antibiotic-induced mild (creatinine=1.5-6.0 mg/dl) and advanced (creatinine>6.0 mg/dl) RF. Conventional microelectrode techniques, western blotting, and histological examinations were performed using the isolated rabbit PV, left atrium (LA), right atrium (RA) and sinoatrial node (SAN)., Results: Advanced RF rabbits (n=18) had a higher incidence (33.3% vs. 11.1% and 0%, p<0.05) of atrial arrhythmia than mild RF (n=18) and control (n=18) rabbits. Advanced RF rabbits exhibited faster PV spontaneous activities, longer action potential duration (APD) in the LA, higher fibrosis in the LA, and slower SAN beating rates than control rabbits, but had a similar APD and fibrosis in the RA. Caffeine (1 mM) increased advanced RF PV arrhythmogenesis, which is blocked by flecainide (10 μM), or KB-R7943 (10 μM). Moreover, advanced RF rabbits had a higher expression of the Na+/Ca2+ exchanger, protein kinase A, phosphorylated ryanodine receptor (Serine 2808), and phosphorylated phospholamban (Serine 16) in PVs, and a higher expression of Cav 1.2 in the LA, and a lower expression of hyperpolarization-activated cyclic nucleotide-gated potassium channel 4 in the SAN., Conclusions: Advanced RF increases atrial arrhythmia by modulating the distinctive electrophysiological characteristics of the PV, LA, and SAN., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Background: Non-steroidal anti-inflammatory drugs (NSAIDs) increase the risk of atrial fibrillation (AF). This study investigated whether selective and non-selective NSAIDs differentially regulate the arrhythmogenesis of pulmonary veins and atria., Methods: Conventional microelectrodes were used to record action potentials (APs) in isolated rabbit PVs, sinoatrial node (SAN), left atrium (LA), and right atrium (RA) preparations before and after celecoxib or indomethacin administration. A whole-cell patch clamp was used to record the sodium-calcium exchanger (NCX) current, L-type calcium current (ICa-L), and late sodium current (INa-late) before and after celecoxib administration in isolated PV cardiomyocytes., Results: Celecoxib (0.3, 1, and 3 μM) reduced PV spontaneous beating rates, and induced delayed afterdepolarizations and burst firings in four of eight PV preparations (50%, p<0.05). Celecoxib also reduced SAN beating rates and decreased AP durations (APDs) in RA and LA, but did not change the resting membrane potential. Indomethacin (0.3, 1, 3, and 10 μM) changed neither the PV or SAN beating rates nor RA APDs, but it reduced LA APDs. Celecoxib (3 μM) significantly increased the NCX current and decreased the ICa-L, but did not change the INa-late. Ranolazine (10 μM) suppressed celecoxib (3 μM)-induced PV burst firings in 6 (86%, p<0.05) of 7 PVs. KB-R7943 (10 μM) suppressed celecoxib (3 μM)-induced PV burst firings in 5 (71%, p<0.05) of 7 PVs., Conclusions: Selective and non-selective NSAIDs differentially modulate PV and atrial electrophysiological characteristics. Celecoxib increased PV triggered activity through enhancement of the NCX current, which contributed to its arrhythmogenesis., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Background: Chronic kidney disease (CKD) is associated with a higher incidence of atrial fibrillation (AF) with unclear mechanisms. Indoxyl sulfate (IS) accumulates in CKD patients. IS increases oxidative stress, which contributes to the genesis of AF. The arrhythmogenic effect of IS is unclear., Methods: Conventional microelectrodes recorded the action potentials (AP) of isolated rabbit left atrium (LA), right atrium (RA), pulmonary vein (PV), and sinoatrial nodes (SANs) before and after treatment with IS with and without an antioxidant (ascorbic acid). Confocal microscopy with fluorescence and whole-cell patch clamp were used to evaluate intracellular calcium in isolated PV cardiomyocytes with and without IS., Results: Compared to the control, IS induced more PV delayed afterdepolarizations at 0.1, 1, 10, and 100 μM, and induced more PV burst firings at 1, 10, and 100 μM. In contrast, IS (10 and 100 μM) reduced the SAN spontaneous beating rate. IS (100 μM) significantly shortened LA AP durations, but not RA. IS (100 μM)-treated PV cardiomyocytes had a similar calcium transient and sarcoplasmic reticulum calcium content, but a larger calcium leak than control PV cardiomyocytes. Burst pacing and isoproterenol induced a greater AF occurrence (50% vs. 100%; P = 0.009) and a longer AF duration (26 ± 9 vs. 5 ± 3 seconds; P < 0.05) in the LA (n = 8) with IS (100 μM) than without IS. Moreover, ascorbic acid (1 mM) attenuated the effects of IS on the LA, PV, and SANs., Conclusion: IS increases PV and atrial arrhythmogenesis through oxidative stress. They may contribute to the occurrence of AF in CKD patients., (© 2014 Wiley Periodicals, Inc.)

Pulmonary veins (PVs) play a critical role in the pathophysiology of atrial fibrillation (AF). Histone deacetylases (HDACs) are vital to calcium homeostasis and AF genesis. However, the electrophysiological effects of HDAC inhibition were unclear. This study evaluated whether HDAC inhibition can regulate PV electrical activity through calcium modulation. Whole-cell patch-clamp, confocal microscopic with fluorescence, and Western blot were used to evaluate electrophysiological characteristics and Ca(2+) dynamics in isolated rabbit PV cardiomyocytes with and without MPT0E014 (a pan HDAC inhibitor), MS-275 (HDAC1 and 3 inhibitor), and MC-1568 (HDAC4 and 6 inhibitor) for 5~8h. Atrial electrical activity and induced-AF (rapid atrial pacing and acetylcholine infusion) were measured in rabbits with and without MPT0E014 (10mg/kg treated for 5 hours) in vivo. MPT0E014 (1 μM)-treated PV cardiomyocytes (n=12) had slower beating rates (2.1 ± 0.2 vs. 2.8 ± 0.1 Hz, p < 0.05) than control PV cardiomyocytes. However, control (n=11) and MPT0E014 (1 μM)-treated (n = 12) SAN cardiomyocytes had similar beating rates (3.2 ± 0.2 vs. 2.9 ± 0.3 Hz). MS-275-treated PV cardiomyocytes (n = 12, 2.3 ± 0.2 Hz), but not MC-1568-treated PV cardiomyocytes (n=14, 3.1 ± 0.3 Hz) had slower beating rates than control PV cardiomocytes. MPT0E014-treated PV cardiomyocytes (n=14) had a lower frequency (2.4 ± 0.6 vs. 0.3 ± 0.1 spark/mm/s, p < 0.05) of Ca(2+) sparks than control PV (n=17) cardiomyocytes. As compared to control, MPT0E014-treated PV cardiomyocytes had reduced Ca(2+) transient amplitudes, sodium-calcium exchanger currents, and ryanodine receptor expressions. Moreover, MPT0E014-treated rabbits had less AF and shorter AF duration than control rabbits. In conclusions, HDAC inhibition reduced PV arrhythmogenesis and AF inducibility with modulation on calcium homeostasis., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

Background: Aging and testosterone deficiency contribute to the pathogenesis of atrial fibrillation (AF). We determine the effects of testosterone replacement on the electrophysiology and arrhythmogenesis of pulmonary vein (PV) and left atrium (LA) in aged rabbits., Methods: Electrocardiography, heart rate variability, echocardiography, Western blot and conventional microelectrodes were used in aged rabbits (age, >2 years) with and without (control) testosterone treatment (10mg/kg, 12 weeks)., Results: Testosterone-treated aged rabbits had longer corrected QT interval, higher low frequency/high frequency, greater left ventricle (LV) mass but lower LA total emptying fraction and LV ejection fraction than control rabbits. In tissue preparations, the spontaneous rate was faster for testosterone-treated PVs than for control PVs. Angiotensin II concentration-dependently increased the amplitude of delayed afterdepolarizations (DADs) in testosterone-treated PVs but only did so at the highest angiotensin II concentration (100 nM) in control PVs. Isoproterenol increased the incidence of early afterdepolarizations (EADs) and DADs in testosterone-treated PVs but not in control PVs. Testosterone-treated PVs had more H2O2-induced burst firing and EADs than control PVs. Testosterone-treated LAs had more isoproterenol-induced DADs and spontaneous activity than did control LAs. However, acetylcholine infusion and rapid atrial pacing (10-20 Hz) induced AF in control LAs but not in testosterone-treated LAs. In addition, as compared with control LAs, testosterone-treated LAs expressed more androgen receptor, β1-adrenergic receptor, and Cav 1.2 and less G protein-coupled receptor kinase-2 and Kv 4.2., Conclusions: Testosterone replacement increased arrhythmogenesis in PV and LA by enhancing adrenergic activity in aged rabbits., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

Background: Sinoatrial node (SAN) dysfunction increases the occurrences of atrial fibrillation (AF). The pulmonary veins (PVs) play a critical role in the pathophysiology of AF. The purpose of this study was to evaluate whether SAN electrical activity can modulate PV arrhythmogenesis., Methods: Conventional microelectrodes and multi-electrode array system were used to simultaneously record the electrical activity and conduction properties of rabbit SAN and PV tissue preparations with and without SAN-PV interruptions before and after perfusion with Anemonia sulcata toxin (ATX)-II (100 nM) or isoproterenol (1 μM)., Results: ATX-II significantly increased PV beating rates, which overdrove SAN electrical activity with the occurrences of PV burst firings in 5 (56%) of 9 tissue preparations, and induced SAN-PV conduction block in 6 (67%) of 9 preparations. After SAN-PV disconnection, ATX-II induced burst firing and early afterdepolarizations in 8 (89%) of 9 PVs. Moreover, the multi-electrode array found that ATX-II reversed the electrical conduction between the SAN and PV with an increase in electrical activity from 1.8 ± 0.6 to 2.9 ± 0.6 Hz (P<0.05) in SAN-PV preparations (n=7). In contrast, isoproterenol did not reverse electrical conduction between the SAN and PV with an increase in electrical activity from 1.8 ± 0.2 to 3.0 ± 0.3 Hz (P<0.005) in SAN-PV preparations (n=7)., Conclusions: SAN electrical activity modulates PV arrhythmogenesis. SAN-PV conduction blocks can increase PV arrhythmogenesis., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

Background: Small-conductance calcium-activated potassium (SK) channels play an important role in atrial electrophysiology. Blocking SK channels prolongs action potential (AP) duration and attenuate electrical remodelling. The effects of SK blocking on the pulmonary vein (PV) and the sinoatrial node (SAN) remain unclear., Materials and Methods: Conventional microelectrodes were used to record the AP in SANs and in isolated rabbit PVs with and without denudation before and after treatment with apamin (1, 10 nM). Using the whole-cell patch-clamp technique, the SK current was investigated in isolated single PV and SAN myocytes., Results: In nondenudated PVs (n = 6), apamin (1 and 10 nM) increased PV spontaneous activity (from 1.8 ± 0.2 Hz to 2.4 ± 0.2 Hz and 2.3 ± 0.2 Hz, P < 0.05) and increased the PV tension by 42 ± 14% and 37 ± 11%. Conversely, in denudated PVs (n = 6), apamin (1 and 10 nM) decreased spontaneous activity (from 2.2 ± 0.3 Hz to 1.9 ± 0.2 Hz and 1.8 ± 0.2 Hz, P < 0.05) and prolonged AP duration without changing PV tensions. Additionally, apamin (1 and 10 nM) decreased spontaneous activity (from 2.8 ± 0.1 Hz to 2.4 ± 0.1 Hz, and 2.4 ± 0.1 Hz, P < 0.05) and prolonged AP duration in SAN (n = 6). SAN myocytes had larger SK currents than did PV cardiomyocytes. Treatment with apamin (10 nM) resulted in a greater decrease (25 ± 8 vs. 20 ± 13%, P < 0.05) in spontaneous activity in isolated single SAN (n = 17) vs. PV cardiomyocytes (n = 16)., Conclusion: Small-conductance calcium-activated potassium channels play a key role in SAN and PV spontaneous activity and AP morphology. Apamin may modulate PV electrical activity with and without endothelium dependence., (© 2013 Stichting European Society for Clinical Investigation Journal Foundation. Published by John Wiley & Sons Ltd.)

Atrial fibrillation (AF) is the most common sustained arrhythmia. Cardiac fibrosis with enhanced extracellular collagen plays a critical role in the pathophysiology of AF through structural and electrical remodeling. Pulmonary veins (PVs) are important foci for AF genesis. The purpose of this study was to evaluate whether collagen can directly modulate PV arrhythmogenesis. Action potentials and ionic currents were investigated in isolated male New Zealand rabbit PV cardiomyocytes with and without collagen incubation (10μg/ml, 5-7h) using the whole-cell patch-clamp technique. Compared to control PV cardiomyocytes (n=25), collagen-treated PV cardiomyocytes (n=22) had a faster beating rate (3.2±04 vs. 1.9±0.2Hz, p<0.005) and a larger amplitude of delayed afterdepolarization (16±2 vs. 10±1mV, p<0.01). Moreover, collagen-treated PV cardiomyocytes showed a larger transient outward potassium current, small-conductance Ca(2+)-activated K(+) current, inward rectifier potassium current, pacemaker current, and late sodium current than control PV cardiomyocytes, but amplitudes of the sodium current, sustained outward potassium current, and L-type calcium current were similar. Collagen increased the p38 MAPK phosphorylation in PV cardiomyocytes as compared to control. The change of the spontaneous activity and action potential morphology were ameliorated by SB203580 (the p38 MAPK catalytic activity inhibitor), indicating that collagen can directly increase PV cardiomyocyte arrhythmogenesis through p38 MAPK activation, which may contribute to the pathogenesis of AF., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Dronedarone and amiodarone are anti-atrial fibrillation agents with different potency. Pulmonary veins play a critical role in the genesis of atrial fibrillation. Oxidative stress can enhance pulmonary vein arrhythmogenesis. This study was done to compare the effects of dronedarone and amiodarone on pulmonary vein electrophysiological and mechanical properties, and oxidative stress-induced arrhythmogenecity. Conventional microelectrodes were used to record action potentials in isolated rabbit pulmonary vein specimens before and after dronedarone and amiodarone with or without the presence of H2O2 (2mM). Dronedarone (0.1, 1 and 10 μM) concentration-dependently decreased pulmonary vein beating rates (from 2.2±0.1 to 1.9±0.1, 1.8±0.1 and 1.7±0.1Hz, n=8, P<0.01). Amiodarone (0.1, 1 and 10 μM) also concentration-dependent decreased pulmonary vein beating rates (from 2.5±0.2 to 2.3±0.2, 2.2±0.2 and 2.0±0.2Hz, n=7, P<0.01). However, dronedarone decreased pulmonary vein beating rates to a greater extent at 0.1 μM (12% versus 4%, P<0.005) and 1μM (17% versus 9%, P<0.005). Dronedarone or amiodarone (0.1, 1 and 10 μM) did not change the pulmonary vein contractility. However, dronedarone (1 and 10 μM) concentration-dependent reduced pulmonary vein diastolic tension by 13±2 mg (P<0.005) and 18±3 mg (P<0.005). In contrast, amiodarone did not change pulmonary vein diastolic tension. Dronedarone (10 μM) and amiodarone (10 μM) attenuated H2O2-induced pulmonary vein burst firings from 100% to 33.3% (P<0.01), and to 0% (P<0.005), respectively. In conclusion, amiodarone and dronedarone both significantly reduced pulmonary vein spontaneous beating rates and H2O2-induced pulmonary vein arrhythmogenesis. However, only dronedarone produced pulmonary vein vasodilation., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Background: Dabigatran reduces stroke in atrial fibrillation. Pulmonary veins (PVs) and left atrium (LA) play a critical role in the pathophysiology of atrial fibrillation. We investigated the effects of thrombin, blood clot solution, and dabigatran on PVs and LA., Methods and Results: Conventional microelectrodes were used to record the action potentials in isolated PV and LA preparations before and after the administration of thrombin or blood clot solution in control and dabigatran-treated rabbits. Thrombin (0.01, 0.1, and 1 unit/mL), respectively, reduced the PV (n=6) spontaneous beating rates from 1.9±0.2 to 1.7±0.2, 1.6±0.2, and 1.4±0.3 Hz (P=0.046). Blood clot solution (0.5% and 5.0%), respectively, reduced the PV (n=5) spontaneous beating rates from 2.0±0.4 to 1.8±0.4 and 1.3±0.3 Hz (P=0.044). Thrombin (0.01, 0.1, and 1 unit/mL) and blood clot solution (0.5% and 5.0%) increased LA diastolic tension and the resting membrane potential with decreased action potential duration and contractility. Thrombin (0.01, 0.1, and 1 unit/mL) and blood clot solution (0.5% and 5%) induced delayed after depolarization and burst firing in PVs, but not in LA. N(G)-nitro-l-arginine methyl ester (100 μmol/L) or a protease-activated receptor type 1 blocker (BMS 200261, 1 μmol/L) attenuated the effects of thrombin and blood clot solution in PVs and LA. Dabigatran-treated PVs had slower spontaneous activity (1.1±0.1 Hz; n=10; P=0.0001 versus control). Their electrophysiological characteristics were not changed by thrombin (1 unit/mL) and blood clot solution (5%)., Conclusions: Thrombin modulates PV and LA electric and mechanical characteristics, which were blocked by dabigatran.

Background: Long QT syndrome (LQTS) is associated with a high incidence of atrial fibrillation (AF), but the underlying mechanisms are unclear. Pulmonary veins (PVs) play a critical role in AF genesis. Type 3 LQTS increases late sodium current (I(Na,L) ), which may increase PV arrhythmogenesis and AF. Therefore, this study examines PV arrhythmogenesis in anemonia sulcata toxin II (ATX-II)-induced type 3 LQTS and evaluates whether the I(Na,L) inhibitor ranolazine can suppress PV arrhythmogenesis., Materials and Methods: Conventional microelectrodes were used to record the action potentials (AP) and contractility in isolated rabbit PV specimens before and after ATX-II administration with or without ranolazine., Results: Anemonia sulcata toxin II (100 nM) increased the PV spontaneous rates from 2·0 ± 0·1 to 2·9 ± 0·2 Hz (n = 7), induced PV burst firing (100%) with the genesis of early afterdepolarization (EAD) (86%) and prolonged the AP duration. Ranolazine (0·1, 1 and 10 μM) dose dependently reduced the PV spontaneous rates from 2·5 ± 0·2 to 2·3 ± 0·2 Hz, 1·9 ± 0·2 and 1·5 ± 0·3 Hz (P < 0·05) and decreased the diastolic tension by 40 ± 19%, 87 ± 26% and 113 ± 28%. In the presence of ranolazine (10 μM), ATX-II (100 nM) further increased the AP duration. However, ATX-II neither increased the PV spontaneous rates (1·6 ± 0·1 vs. 1·7 ± 0·2 Hz, n = 7) nor induced PV burst firing or EAD. Moreover, ranolazine (10 μM) reduced ATX-II-induced PV acceleration and EAD., Conclusions: The I(Na,L) enhancer ATX-II can increase PV arrhythmogenesis, which can be attenuated or blocked by ranolazine. This suggests that AF may be related to type 3 LQTS through increased I(Na,L) ., (© 2012 The Authors. European Journal of Clinical Investigation © 2012 Stichting European Society for Clinical Investigation Journal Foundation.)

Background: Amyloid peptides modulate cardiac calcium homoeostasis and play an important role in the pathophysiology of atrial fibrillation. Pulmonary veins (PVs) are critical in the genesis of atrial fibrillation and contain abundant amyloid peptides. Therefore, the purpose of this study is to investigate whether amyloid peptides may change the PV electrical activity through regulating calcium homoeostasis., Methods and Results: The channel and calcium-handling protein expressions, intracellular calcium and ionic currents were studied in isolated rabbit PV cardiomyocytes in the presence and absence (control) of beta-amyloid (Aβ(25-35) ) for 4-6 h, using Western blot analysis, indo-1 fluorimetric ratio and whole-cell patch clamp techniques. Aβ(25-35) decreased the expressions of Ca(V) 1.2, total or Ser16-phosphorylated phospholamban (p-PLB), p-PLB/PLB ratio, sodium/calcium exchanger, but did not change ryanodine receptor, sarcoplasmic reticulum (SR) ATPase and K(+) channel proteins (Kir2.1, Kir2.3, Kv1.4, Kv1.5 and Kv4.2). Aβ(25-35) -treated cardiomyocytes had smaller calcium transient, SR calcium store, L-type calcium current and sodium/calcium exchanger current than control cardiomyocytes. Moreover, Aβ(25-35) -treated cardiomyocytes (n = 20) had shorter 90% of the action potential duration (82 ± 3 vs. 93 ± 5 ms, P < 0·05) than control cardiomyocytes (n = 16)., Conclusion: Aβ(25-35) has direct electrophysiological effects on PV cardiomyocytes., (© 2011 The Authors. European Journal of Clinical Investigation © 2011 Stichting European Society for Clinical Investigation Journal Foundation.)

Introduction: Ivabradine is a novel heart rate decreasing agent with selective and specific antagonist effects on the pacemaker current (I(f)). The aim of this study was to investigate the pharmacological effects of ivabradine on the pulmonary vein (PV) cardiomyocytes., Methods and Results: Whole-cell patch-clamp techniques and the indo-1 fluorimetric ratio technique were used to investigate the characteristics of the I(f) and intracellular calcium (Ca(2+)(i)) in single isolated rabbit PV cardiomyocytes with pacemaker activity before and after an ivabradine administration (0.3, 3, 10, and 30 μM). Ivabradine (0.3, 3, 10, and 30 μM) concentration dependently decreased the spontaneous activity by 6 ± 3%, 32 ± 6%, 49 ± 5%, and 85 ± 4%, and decreased the I(f) by 35 ± 8%, 47 ± 9%, 62 ± 5%, and 65 ± 7%, respectively, in PV cardiomyocytes. The decreased extent of the PV beating rate or I(f) by the different concentrations of ivabradine correlated well with the baseline PV beating rates. The IC(50) of the spontaneous activity and I(f) induced by ivabradine were 9.5 and 3.5 μM, respectively. Moreover, ivabradine (30 μM, but not 3 μM) decreased the Ca(2+)(i) transient in the PV cardiomyocytes and ivabradine (30 μM) decreased the L-type calcium current in the PV cardiomyocytes., Conclusion: Ivabradine decreased the I(f)s and Ca(2+)(i) transient in the PV cardiomyocytes, which may contribute to its inhibitory effects on the PV spontaneous activity., (© 2011 Wiley Periodicals, Inc.)

Ischaemia and reperfusion contribute to the genesis of AF (atrial fibrillation). PVs (pulmonary veins) and the atria are important foci for AF initiation and maintenance. However, the effect of ischaemia and reperfusion on PVs and the atria has not yet been fully elucidated. In the present study, conventional microelectrodes were used to record the APs (action potentials) in isolated rabbit PV, LA (left atrium) and RA (right atrium) specimens during hypoxia and reoxygenation, and pharmacological interventions. Hypoxia reduced the PV beating rates from 1.8±0.1 to 1.3±0.2 and 0.8±0.1 Hz at 30 and 60 min respectively (n=8, P<0.005), and induced EAD (early after depolarization) in three (37.5%) of the PVs and DAD (delayed after depolarization) in one (12.5%) of the PVs. Reoxygenation increased the PV spontaneous rate to 1.4±0.2 Hz (P<0.05) and induced PV burst firings (3.5±0.1 Hz, P<0.001) in six (75%) of the PVs. Hypoxia shortened the AP duration in the LA and PVs, but not in the RA. Pretreatment with glibenclamide attenuated hypoxia-induced decreases in the PV spontaneous activity and the shortening of the LA and PV AP duration. Similar to those in hypoxia, the K(ATP) (ATP-sensitive potassium) channel opener pinacidil (30 μM) decreased PV spontaneous activity and shortened the AP duration. Pretreatment with 5 mM N-MPG [N-(mercaptopropionyl)glycine; a hydroxyl (•OH) free-radical scavenger] or 300 μM chloramphenicol [a cytochrome P450 inhibitor that reduces ROS (reactive oxygen species)] attenuated the rate changes induced by hypoxia and reoxygenation, and also decreased the burst firing incidence. In conclusion, hypoxia and reoxygenation significantly increased PV arrhythmogenesis and induced different electrophysiological responses in the RA and LA, which may play a role in the pathophysiology of AF.

Unlabelled: Late sodium currents and intracellular Ca(2+) (Ca(2+) (i)) dynamics play an important role in arrhythmogenesis of pulmonary vein (PV) and heart failure (HF). It is not clear whether HF enhances PV arrhythmogenesis through modulation of Ca(2+) homeostasis and increased late sodium currents. The aim of this study was to investigate the sodium and calcium homeostasis in PV cardiomyocytes with HF., Methods and Results: Whole-cell patch clamp was used to investigate the action potentials and ionic currents in isolated rabbit single PV cardiomyocytes with and without rapid pacing induced HF. The Ca(2+) (i) dynamics were evaluated through fluorescence and confocal microscopy. As compared to control PV cardiomyocytes (n = 18), HF PV cardiomyocytes (n = 13) had a higher incidence of delayed afterdepolarization (45% vs 13%, P < 0.05) and faster spontaneous activity (3.0 ± 0.2 vs 2.1 ± 0.2 Hz, P < 0.05). HF PV cardiomyocytes had increased late Na(+) currents, Na(+) /Ca(2+) exchanger currents, and transient inward currents, but had decreased Na(+) currents or L-type calcium currents. HF PV cardiomyocytes with pacemaker activity had larger Ca(2+) (i) transients (R410/485, 0.18 ± 0.04 vs 0.11 ± 0.02, P < 0.05), and sarcoplasmic reticulum Ca(2+) stores. Moreover, HF PV cardiomyocytes with pacemaker activity (n = 18) had higher incidence (95% vs 70%, P < 0.05), frequency (7.8 ± 3.1 vs 2.3 ± 1.2 spark/mm/s, P < 0.05), amplitude (F/F(0) , 3.2 ± 0.8 vs 1.9 ± 0.5, P < 0.05), and longer decay time (65 ± 3 vs 48 ± 4 ms, P < 0.05) of Ca(2+) sparks than control PV cardiomyocytes with pacemaker activity (n = 18)., Conclusions: Dysregulated sodium and calcium homeostasis, and enhanced calcium sparks promote arrhythmogenesis of PV cardiomyocytes in HF, which may play an important role in the development of atrial fibrillation., (© 2011 Wiley Periodicals, Inc.)

Activation of the atrial renin-angiotensin system plays an important role in the pathophysiology of atrial fibrillation (AF). The pulmonary vein (PV) and left atrium (LA) are important trigger and substrate for the genesis of AF. We investigate the effects of a direct renin inhibitor, aliskiren, on the PV and LA arrhythmogenic activity and the underlying electromechanical mechanisms. Conventional microelectrodes were used to record action potentials and contractility in isolated rabbit PVs and LA tissues before and after the administration of aliskiren (0.1, 1, 3 and 10 μM). By the whole-cell patch clamp and indo-1 fluorimetric ratio techniques, ionic currents and intracellular calcium transient were studied in isolated single PV and LA cardiomyocyte before and after the administration of aliskiren (3 μM). Aliskiren (0.1, 1, 3 and 10 μM) reduced PV firing rate in a concentration-dependent manner (6, 10, 14 and 17%) and decreased PV diastolic tension, which could be attenuated in the presence of 100 μM L-N(G)-Nitroarginine Methyl Ester (L-NAME). Aliskiren induced PV automatic rhythm exit block causing slow and irregular PV activity with variable pauses. Aliskiren increased PV and LA contractility, which could be abolished by pre-treating with 0.1 μM ryanodine. Aliskiren (3 μM) decreased L-type calcium currents, but increased reverse-mode of Na( + )/Ca(2+ ) exchanger currents, intracellular calcium transients, and sarcoplasmic reticulum calcium content in PV and LA cardiomyocytes. Pretreatment with renin, losartan or angiotensin II did not alter the effect of aliskiren on sarcolemmal calcium flux. In conclusion, aliskiren reduces PV arrhythmogenic activity with a direct vasodilatory property and has a positive inotropic effect on cardiomyocytes. These findings may reveal the anti-arrhythmic and anti-heart failure potentials of aliskiren.

1. Heart failure (HF) predisposes to atrial fibrillation (AF) as a result of substrate remodelling. The present study aimed to investigate the impact of HF on the electrical remodelling of the pulmonary veins (PV) and left atrium (LA). 2. The electrical activity was recorded in LA and PV from control rabbits and rabbits with rapid ventricular pacing-induced HF, using a multi-electrode array system and conventional microelectrodes. 3. Compared with the control-PV (n = 21), the HF-PV (n = 13) had a higher incidence and frequency of rapid pacing-induced spontaneous activity (85 vs 29%, P = 0.005; 3.5 ± 0.2 vs 1.7 ± 0.1 Hz, P < 0.001) and high-frequency irregular electrical activity (92 vs 38%, P = 0.01; 23 ± 1 vs 19 ± 1 Hz, P = 0.003), greater depolarized resting membrane potential (-59 ± 1 vs -70 ± 2 mV, P < 0.001), higher incidence of early afterdepolarizations (EAD; 69 vs 6%, P = 0.001) and delayed afterdepolarizations (DAD; 92 vs 25%, P = 0.001), and slower conduction velocity (38 ± 2 vs 63 ± 2 cm/s, P < 0.05). In comparison to the HF-LA, the HF-PV had a higher incidence of spontaneous activity and high-frequency irregular electrical activity (85 vs 39%, P = 0.04; 92 vs 46%, P = 0.03), and higher incidence of EAD and DAD, and those differences were not found between the control-LA and control-PV. The control-PV with high-frequency irregular electrical activity had a higher incidence of DAD and spontaneous activity as compared with those without it. 4. HF contributed to an increased automaticity, triggered activity and conduction disturbance in the PV. The PV possessed more arrhythmogenic properties, which might play an important role in the genesis of AF in HF., (© 2011 The Authors. Clinical and Experimental Pharmacology and Physiology © 2011 Blackwell Publishing Asia Pty Ltd.)

Background: Sex and the autonomic nervous system play critical roles in the pathophysiology of atrial fibrillation (AF). Sex differences in electrophysiological characteristics of the pulmonary veins (PVs, AF initiator) and left atrium (LA, AF substrate) are not clear., Methods and Results: Conventional microelectrodes were used to record the action potential in isolated PV and LA tissue preparations from male and female (age, 8≈10 months) rabbits before and after drug administration (adenosine, acetylcholine, and isoproterenol). Male PVs (n = 7) had a higher spontaneous beating rate (1.7 ± 0.2 versus 1.2 ± 0.1 Hz, P = 0.021) and incidence of burst firing (72% versus 11%, P = 0.038) than female PVs (n = 9). Male PVs without spontaneous activity (n = 10) and the LA (n = 11) had longer action potential durations than female PVs (n = 9) and LA (n = 9). Additionally, male PVs had a more-positive resting membrane potential (79 ± 3 versus 84±2 mV, P=0.022). Isoproterenol (3 μmol/L) increased the delayed afterdepolarizations to a greater extent in male than in female PVs. In PVs without spontaneous activity or LA, isoproterenol (0.1 and 3 μmol/L) consistently shortened the action potential durations in females but not in males. Acetylcholine (5.5 μmol/L) decreased the spontaneous activity of PVs and shortened the action potential durations in both groups. Adenosine (10 μmol/L) also similarly decreased the spontaneous activity of PVs and delayed afterdepolarizations in both groups., Conclusions: There are significant sex differences in PV and LA action potential characteristics in rabbits. The higher amplitude of delayed afterdepolarizations after isoproterenol superfusion in male PVs may contribute to sex-related arrhythmogenesis.

Aims: Omega-3 polyunsaturated fatty acids can modulate cardiac electrophysiology and reduce the genesis of atrial fibrillation. This study investigates the potential mechanisms through which eicosapentaenoic acid (EPA) reduces pulmonary vein (PV) arrhythmogenesis., Main Methods: Conventional microelectrodes were used to record the action potentials (APs), before and after the EPA (0.1 μM and 1.0 μM) administration with and without the presence of a nitric oxide (NO) synthase inhibitor (L-NAME, 100 μM) in isolated rabbit PV tissue preparations. Furthermore, indo-1 fluorimetric ratio technique was used to evaluate intracellular calcium in isolated single PV cardiomyocytes with or without incubation of EPA (1.0 μM, 30 min)., Key Findings: EPA concentration-dependently reduced the PV spontaneous beating rate (P<0.05). EPA (1.0 μM) also reduced the amplitude of delayed afterdepolarizations (P<0.05). EPA hyperpolarized the maximal diastolic potential (MDP), shortened AP duration, increased AP amplitude (APA), and reduced diastolic tension and contractility. However, EPA in the presence of L-NAME or omega-9 fatty acids (oleic acid, 1.0 μM) did not have any effect on PV spontaneous activity, AP morphology, or contractile force. A linear regression shows that the decrease in PV spontaneous beating rates induced by EPA correlated well with the changes of MDP, APA, diastolic tension, and contractile force of PVs. In addition, intracellular Ca(2+) transient and sarcoplasmic reticulum Ca(2+) content were significantly more decreased in the EPA-treated cardiomyocytes than in control PV cardiomyocytes as observed by indo-1 fluorescence., Significance: EPA reduces PV arrhythmogenesis through the mechanoelectrical feedback generated by NO production., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Introduction: Heat stress-induced responses reduce the occurrence of atrial fibrillation (AF). Pulmonary vein (PV) cardiomyocytes with pacemaker activity play a critical role in the pathophysiology of AF. In this study, we examined whether heat-stress responses alter the electrophysiological characteristics of PV cardiomyocytes and protect the PV against angiotensin II- or isoproterenol-induced arrhythmogenesis., Methods and Results: We used whole-cell patch clamp techniques to investigate the spontaneous activity and ionic currents in single isolated rabbit PV pacemaker cardiomyocytes with or without (control) exposure to heat stress (43°C, 15 minutes) 5 ± 1 hours before the experiments. Compared to control cardiomyocytes, heat-stressed PV cardiomyocytes had slower beating rates. Heat-stressed PV cardiomyocytes had larger L-type calcium currents, transient outward currents, smaller inward rectifier potassium currents, but similar sodium-calcium exchanger currents. Additionally, heat-stressed PV cardiomyocytes had a lower incidence of pacemaker currents than control PV cardiomyocytes. Moreover, isoproterenol increased the beating rate of control cardiomyocytes but not heat-stressed PV cardiomyocytes. Similarly, angiotensin II also increased the beating rate of control cardiomyocytes, but not heat-stressed PV cardiomyocytes, in association with decreased expression of the angiotensin II type 1 receptor., Conclusion: Heat-stress responses altered the electrophysiological characteristics of PV cardiomyocytes and attenuated the effects of isoproterenol and angiotensin II on PV arrhythmogenesis, which may play a role in the protective potential of heat-stress responses., (© 2010 Wiley Periodicals, Inc.)

Background: Oxidative stress and pulmonary veins (PVs) play critical roles in the pathophysiology of atrial fibrillation. The purpose of the present study was to investigate whether oxidative stress and antioxidant agents can change the electrophysiological characteristics of the left atrium (LA) and PVs., Methods and Results: Conventional microelectrodes were used to record the action potentials (APs) in isolated rabbit PV and LA specimens before and after H(2)O(2) administration with or without ascorbic acid or N-mercaptopropionyl-glycine (N-MPG, a free radical .OH scavenger). H(2)O(2) (0.02 and 0.2 mmol/L) decreased the PV spontaneous rates from 2.0+/-0.1 Hz to 1.6+/-0.1 Hz, and 1.7+/-0.1 Hz (n=10, P<0.05), but H(2)O(2) (2 mmol/L) increased PV spontaneous rates from 2.0+/-0.1 Hz to 2.8+/-0.2 Hz. H(2)O(2) easily induced PV burst firing and early afterdepolarizations, but not in the LA. H(2)O(2) shortened the AP duration and increased the contractile force to a greater extent in the LA than in PVs. In addition, the H(2)O(2)-induced PV burst firing and increasing spontaneous rates were suppressed or attenuated by pretreatment with ascorbic acid (1 mmol/L) or N-MPG (10 mmol/L)., Conclusions: H(2)O(2) significantly changed the electrophysiological characteristics of PV and LA through activation of free radicals and may facilitate the occurrence of atrial fibrillation.

Background: Pulmonary veins (PVs) are the most important sources of ectopic beats with the initiation of paroxysmal atrial fibrillation, or the foci of ectopic atrial tachycardia and focal atrial fibrillation. Elimination of nitric oxide (NO) enhances cardiac triggered activity, and NO can decrease PV arrhythmogenesis through mechano-electrical feedback. However, it is not clear whether NO may have direct electrophysiological effects on PV cardiomyocytes. This study is aimed to study the effects of nitroprusside (NO donor), on the ionic currents and arrhythmogenic activity of single cardiomyocytes from the PVs., Methods: Single PV cardiomyocytes were isolated from the canine PVs. The action potential and ionic currents were investigated in isolated single canine PV cardiomyocytes before and after sodium nitroprusside (80 muM,) using the whole-cell patch clamp technique., Results: Nitroprusside decreased PV cardiomyocytes spontaneous beating rates from 1.7 +/- 0.3 Hz to 0.5 +/- 0.4 Hz in 9 cells (P < 0.05); suppressed delayed after depolarization in 4 (80%) of 5 PV cardiomyocytes. Nitroprusside inhibited L-type calcium currents, transient outward currents and transient inward current, but increased delayed rectified potassium currents., Conclusion: Nitroprusside regulates the electrical activity of PV cardiomyocytes, which suggests that NO may play a role in PV arrhythmogenesis.

Introduction: The relationship between the determining factors and beating rates of pulmonary vein (PV) pacemaker cardiomyocytes has not been fully elucidated. The purposes of this study were to compare the electrophysiological characteristics between PV fast and slow pacemaker cardiomyocytes., Methods: Whole-cell patch clamp was used to investigate the action potentials, transient outward currents (I(to)), sustained outward potassium currents (I(Ksus)), rapid delayed rectifier potassium currents (I(Kr)), inward rectifier potassium current (I(K1)), pacemaker currents (I(f)), and transient inward currents in isolated rabbit PV single fast (> or =2.5 Hz) and slow (<2.5 Hz) pacemaker cardiomyocytes., Results: The fast PV pacemaker cardiomyocytes (n = 66) had lesser negative maximum diastolic potential (-53 +/- 1 mV vs -59 +/- 1 mV, P < 0.001) and larger slope of diastolic depolarization (0.31 +/- 0.02 V/sec vs 0.09 +/- 0.01 V/sec, P < 0.001) than slow PV pacemaker cardiomyocytes (n = 65). Moreover, the PV beating rates correlated well with the slope of diastolic depolarization and maximum diastolic potential with a linear regression. As compared to those in slow PV pacemaker cardiomyocytes, the fast PV pacemaker cardiomyocytes had smaller I(to) and I(K1), and larger I(f) but with similar I(Ksus,)I(Kr), and transient inward currents. However, only few fast (2/34) and slow (1/23) PV pacemaker cardiomyocytes contained barium-sensitive hyperpolarization-activated time-dependent current (I(KH))(.), Conclusions and Implications: The fast and slow PV pacemaker had different electrophysiological characteristics. I(to), I(K1), and I(f) may regulate the beating rates of PV pacemaker cardiomyocytes.

Aims: Lactic acidosis causes atrial fibrillation (AF), and pulmonary veins (PVs) are the most important focus for the generation of AF. Cariporide (HOE642), a Na(+)/H(+) blocker, can prevent atrial tachycardia-induced electrical remodeling. The purpose of this study was to investigate whether cariporide can prevent lactic acidosis-induced PV arrhythmogenesis., Main Methods: Conventional microelectrodes were used to record the action potentials (APs) before and after the administration of lactic acid (10 and 20 mM) in the absence and presence of cariporide (10 microM) pretreatment in isolated rabbit PV and atrial tissue preparations., Key Findings: Lactic acidosis of 10 mM (pH 7.0+/-0.1) and 20 mM (pH 6.7+/-0.1) reduced PV (n=6) spontaneous rates from 2.5+/-0.3 to 1.6+/-0.4 (by 36+/-1%) and 1.1+/-0.4 Hz (by 56+/-2%), respectively, but lactic acidosis (10 and 20 mM) induced 12 episodes (3.9+/-0.2 Hz) and 23 episodes (4.0+/-0.3 Hz) of non-sustained burst firings in 4 PV specimens. Lactic acidosis (10 and 20 mM) decreased the AP amplitude (APA) and velocity of depolarization (Vmax), but increased the resting membrane potential (RMP), AP duration, and strength-response interval (SRI) in the PV and atrium. In the presence of cariporide (10 microM), lactic acidosis (10 and 20 mM) only reduced PV spontaneous rates from 2.4+/-0.2 to 1.8+/-0.4 (by 25+/-1%) and 1.6+/-0.4 Hz (by 33+/-1%), respectively, and prevented lactic acidosis-induced PV burst firings. Cariporide also reduced the effects of lactic acidosis on the RMP, AP duration, APA, Vmax, and SRI., Significance: Lactic acidosis has significant arrhythmogenic effects on PVs, which may be attenuated by Na(+)/H(+) blockers.

1. Pulmonary veins are the most important focus for the initiation of atrial fibrillation. Diabetes mellitus may be associated with hypertonicity and increased occurrence of atrial fibrillation. 2. The purpose of the present study was to investigate whether hypertonicity alters the electrophysiological characteristics of pulmonary veins and atria to enhance the genesis of atrial fibrillation. 3. A whole-cell patch-clamp technique was used to investigate action potentials and ionic currents in rabbit isolated single pulmonary vein and atrial cardiomyocytes during immersion in isotonic and hypertonic (1.2x normal osmolality) solutions. 4. Hypertonicity increased the spontaneous beating rates of pulmonary vein cardiomyocytes from 2.3 +/- 0.3 to 3.4 +/- 0.3 Hz (n = 11; P < 0.001). Hypertonicity prolonged action potential duration to a greater extent in atrial cardiomyocytes than in pulmonary vein cardiomyocytes. Compared with atrial cardiomyocytes, hypertonicity increased the transient inward currents and Na(+)/Ca(2+) exchange currents to a greater extent in pulmonary vein cardiomyocytes, but decreased the delayed rectified potassium currents to a lesser extent. 5. Hypertonicity plays an important role in the electrical activity of pulmonary vein and atrial cardiomyocytes, which may have a potential role in the pathophysiology of atrial fibrillation.

Introduction: Pulmonary veins (PVs) are the most important focus for the generation of atrial fibrillation. The HMG-CoA reductase inhibitors (statins) can reduce the occurrence of atrial fibrillation. The purposes of this study were to evaluate whether statins may inhibit the PV arrhythmogenic activity to prevent atrial arrhythmias from PVs and to investigate the link between fluvastatin, nitric oxide synthase (NOS) activity, mechanical activity, and electrical activity., Methods: Conventional microelectrodes and Western blot were used to record the electrical activity, diastolic tension, contractility and expression of Akt, endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), and phosphorylated Akt and eNOS before and after the administration of fluvastatin in rabbit PVs or atria., Results: Fluvastatin decreased the PV spontaneous activity, diastolic tension, and contractility, but did not change the action potential duration or resting membrane potential. The effects of fluvastatin on the PV firing rate and diastolic tension were attenuated in the presence of L-NAME (100 microM), wortmannin (100 nM), and ODQ (3 microM). Fluvastatin (1 muM) increased the phosphorylated Akt and eNOS, but did not change the total Akt or eNOS in the PVs and atria. In contrast, fluvastatin (1 microM) decreased the total nNOS in the PVs and atria., Conclusions and Implications: Fluvastatin produced nitric oxide through the PI3kinase/Akt pathway, thus reducing the PV vascular diastolic tension and PV spontaneous activity. These results may contribute to the beneficial effects of statins.

Introduction: Coronary artery disease (CAD) is an important etiology of atrial fibrillation (AF). Coronary artery calcification is a marker of coronary atherosclerosis and coronary events. The purpose of this study was to investigate whether larger left atrium (LA) and pulmonary veins (PVs) were seen by multidetector computed tomography (MDCT) scans in those patients with higher coronary calcium scores., Methods and Results: A total of 166 patients undergoing MDCT for general check-up (n = 128, 77%) or suspected CAD (n = 38, 23%) were enrolled and divided into a control (calcium score = 0, n = 60), medium calcium score (calcium score = 100 approximately 400, n = 47), and high calcium score (calcium score >400, n = 59) groups. Diameters and areas of the LA, left atrial appendage (LAA), and PVs were measured by MDCT. The high calcium score group had significantly larger PVs diameters, LAA orifice area (1.9 +/- 1.4 cm(2), 0.9 +/- 0.5 cm(2), 0.8 +/- 0.4 cm(2), P < 0.005), LA anterior-posterior distance (32.2 +/- 6.8 mm, 30.4 +/- 6.5 mm, 27.3 +/- 6.0 mm, P < 0.05), and transverse distance (52.6 +/- 7.3 mm, 50.2 +/- 9 mm, 49.5 +/- 4.6 mm, P < 0.05) than the medium calcium score and control groups. Six (3.6%) patients with paroxysmal AF had higher calcium scores and larger diameters of LA, LAA, and PVs than those (96.4%) without paroxysmal AF. Two patients in the high calcium score group had calcified PVs localized to the right upper and left upper PVs. The incidence of calcified PVs was 1.2% for the total patients and 3.3% for the high calcium score patients., Conclusion: In the presence of high calcium scores in this patient population, the LA, LAA, and PVs were enlarged.