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Objective: Short QT syndrome (SQTS) is characterized by ventricular arrhythmias and sudden death. One form of SQTS is caused by mutation N588K in human ether-a-go-go-related gene (HERG). In this study we sought to determine the potential role of N588K in arrhythmias. Methods: We measured the characteristics of HERG current generated by wild-type (WT) KCNH2 and the N588K mutant channel expressed in mammalian TSA201 cells. Results: Whole-cell patch-clamp recordings of WT HERG currents showed the usual rapid onset of inactivation (rectification) at potentials more positive than +10 mV. In contrast, N588K currents rectified at potentials over +80 mV. Over the physiological range of potentials, N588K currents do not inactivate. During an action potential clamp, WT currents displayed a “hump” like waveform with slow activation kinetics and a rapid increase during phase 3 repolarization. In contrast, N588K currents were proportional to the amplitude of the action potential and displayed a dome-like configuration and a much larger current during the initial phases in the ventricle. Purkinje cell action potentials display a more negative phase 2 repolarization than the ventricle and elicited much smaller WT and N588K currents of similar amplitudes. Conclusions: Physiologically the N588K mutation abolishes rectification of HERG currents and specifically increases I Kr in the ventricle with minimal effects on the Purkinje fiber action potential duration. Such preferential prolongation may explain the separation of the T and U waves observed in the ECG of SQTS patients and lead to re-excitation of the ventricle endocardium. [Copyright &y& Elsevier]

Abstract: Objective: To determine the presence and the potential contribution of neuronal sodium channels to dog cardiac function. Methods: We used a combination of electrophysiological (patch clamp), RT-PCR, biochemical and immunohistochemical techniques to identify and localize neuronal Na+ channels in dog heart and determine their potential contribution to the fast sodium current. Results: In all cardiac tissues investigated, Nav1.1, Nav1.2 and Nav1.3 transcripts were detected. In immunoblots, we found Nav1.1 and Nav1.2 proteins in the ventricle (V) and in Purkinje fibers (PF). Nav1.3 immunoblots suggested strong proteolytic activity against this isoform in the heart. Nav1.6 was not found in any of the tissues tested. Confocal immunofluorescence on cardiac myocytes showed that Nav1.1 was predominantly localized at the intercalated disks in V and PF and around the nucleus (V). Nav1.2 was only present at the Z lines (V). Consistent with the immunoblot data, an intense but diffuse intracellular staining was observed for Nav1.3. Nav1.6 fluorescence staining was faint and diffuse. Surprisingly, immunoblots indicated the presence of two Navβ2 variants: a 42-kDa protein that co-localized with Nav1.2 at the Z lines in V and a 34-kDa protein that co-localized with Nav1.1 at the intercalated disks in PF. In agreement with the biochemical data, electrophysiological results suggest that neuronal sodium channels generate 10±5% and 22±5% of the peak sodium current in dog ventricle and Purkinje fibers, respectively. Conclusions: Our results suggest that neuronal NaChs are more abundant in Purkinje fibers than in ventricles, and this suggests a role for them in cardiac conduction. [Copyright &y& Elsevier]

Objective: In animal models of hypertrophy, electrical remodeling giving rise to QT prolongation occurs rapidly and is associated with the development of torsade de pointes (TdP) arrhythmias and sudden death. Chronic AV block (CAVB)-induced hypertrophy in dogs has been associated with a reduction in the slow component (IKs) of the delayed rectifier potassium current (IK), which contributes to a prolongation of ventricular repolarization, the development of an acquired form of long QT, and the substrate for triggered activity and TdP. The present study was designed to probe the molecular basis for the decrease in IKs by studying the characteristics of KCNE1 and KCNQ1, the putative genes responsible for formation of the channel. Methods and Results: Using a combination of Northern blot, competitive multiplex PCR and immunoblot assays, we found that CAVB reduces KCNE1 and KCNQ1 RNA in the canine ventricles by 70 and 80%, respectively. Protein levels of KCNE1 and KCNQ1 were reduced by 60 and 50%, respectively. We also demonstrate at the molecular level the basis for inter-ventricular difference in IKs density previously reported in hearts of normal dogs and show the basis for reduction of this difference in the CAVB dog. Conclusions: Our results indicate that the CAVB-induced reduction in IKs is due to a down-regulation of KCNE1 and KCNQ1 transcription. The data suggest that electrical remodeling of the cardiac ventricle during hypertrophy involves regulation of the gene expression through modulation of transcriptional and translational regulatory pathways. The reduction in KCNE1 and KCNQ1 expression increases the dependence of ventricular repolarization on the rapid component of IK and may potentiate the action of Class III antiarrhythmic agents. [Copyright &y& Elsevier]

Objectives: In the present study, we describe the characteristics and examine the anticoagulation levels and safety of subcutaneous enoxaparin in unstable angina (UA)/non-ST-segment elevation myocardial infarction (NSTEMI) patients who would not have been eligible in the Efficacy Safety Subcutaneous Enoxaparin in Non-Q-wave Coronary Events (ESSENCE) and Thrombolysis In Myocardial Infarction (TIMI)-11B trials.Background: It is not known whether the benefit shown with enoxaparin in the selected population of pivotal trials can be extended to the real world.Methods: In our center, all patients with UA/NSTEMI are anticoagulated with subcutaneous enoxaparin adjusted to creatinine clearance. Among 515 consecutive patients, we identified 174 who would not have been eligible for ESSENCE or TIMI-11B ("EP" group for excluded patients). We evaluated cardiovascular death or non-fatal myocardial infarction (MI), as well as major and minor bleeding events, at 30 days in the EP group and in patients without any of the exclusion criteria ("NEP" group for non-excluded patients).Results: This EP group was older, had a higher female/male ratio, and more frequently had a history of MI or a diagnosis of non-Q MI on admission than the NEP group. The distribution of the anti-Xa activity was similar in both groups. The bleeding rates (major and minor) at 30 days were similar in the EP and NEP groups (2.3% vs. 2.9%, respectively, P = NS). On multivariate analysis, the use of glycoprotein IIb/IIIa inhibitors and the presence of hypertension were the only independent predictors of bleeding found in the whole population. Compared with the NEP group, the EP group had a fourfold increased rate of death or MI at 30 days (15.5% vs. 4.1%, p < 0.01). On multivariate analysis, the independent predictors of death or MI at 30 days were NSTEMI on admission, creatinine clearance, and heart failure.Conclusions: Patients who do not fit the enrollment criteria of ESSENCE/TIMI-11B have higher risk baseline characteristics for both bleeding and ischemic events. In these patients, enoxaparin with dose adjustment to creatinine clearance provides adequate anti-Xa levels and no excess of bleeding. [ABSTRACT FROM AUTHOR]

Lamotrigine is widely prescribed to treat bipolar neurological disorder and epilepsy. It exerts its antiepileptic action by blocking voltage-gated sodium channels in neurons. Recently, the US Food and Drug Administration issued a warning on the use of Lamotrigine after observations of conduction anomalies and Brugada syndrome patterns on the electrocardiograms of epileptic patients treated with the drug. Brugada syndrome and conduction disturbance are both associated with alterations of the cardiac sodium current (I Na ) kinetics and amplitude. In this study, we used the patch clamp technique on cardiomyocytes from epileptic rats to test the hypothesis that Lamotrigine also blocks I Na in the heart. We found that Lamotrigine inhibited 60% of I Na peak amplitude and reduced cardiac excitability in epileptic rats but had little effect in sham animals. Moreover, Lamotrigine inhibited 67% of I NaL and, more importantly, prolonged the action potential refractory period in epileptic animals. Our results suggest that enhanced affinity of Lamotrigine for I Na may in part explain the clinical phenotypes observed in epileptic patients.

Voltage-gated ion channels play a key role in the action potential (AP) initiation and its propagation in sensory neurons. Modulation of their activity during chronic inflammation creates a persistent pain state. In this study, we sought to determine how peripheral inflammation caused by complete Freund's adjuvant (CFA) alters the fast sodium (I Na ), L-type calcium (I CaL ), and potassium (I K ) currents in primary afferent fibers to increase nociception. In our model, intraplantar administration of CFA induced mechanical allodynia and thermal hyperalgesia at day 14 post-injection. Using whole-cell patch-clamp recording in dissociated small (C), medium (Aδ), and large-sized (Aβ) rat dorsal root ganglion (DRG) neurons, we found that CFA prolonged the AP duration and increased the amplitude of the tetrodotoxin-resistant (TTX-r) I Na in Aβ fibers. In addition, CFA accelerated the recovery of I Na from inactivation in C and Aδ nociceptive fibers but enhanced the late sodium current (I NaL ) only in Aδ and Aβ neurons. Inflammation similarly reduced the amplitude of I CaL in each neuronal cell type. Fourteen days after injection, CFA reduced both components of I K (I Kdr and I A ) in Aδ fibers. We also found that I A was significantly larger in C and Aδ neurons in normal conditions and during chronic inflammation. Our data, therefore, suggest that targeting the transient potassium current I A represents an efficient way to shift the balance toward antinociception during inflammation, since its activation will selectively decrease the AP duration in nociceptive fibers. Altogether, our data indicate that complex interactions between I K , I Na , and I CaL reduce pain threshold by concomitantly enhancing the activity of nociceptive neurons and reducing the inhibitory action of Aβ fibers during chronic inflammation., (© 2021 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

Background: Standardization of aortic valve repair by the external ring annuloplasty approach is an alternative to valve replacement to avoid prosthetic valve-related events. Although the benefit of exercise training to improve postoperative exercise tolerance has been demonstrated in many conditions after cardiac surgery, it has never been described after aortic valve repair., Objectives: To evaluate the feasibility of an early exercise training programme after aortic valve repair., Methods: Consecutive patients were prospectively included in 13 postoperative centres. Patients underwent an exercise training programme for approximately 3-5 weeks. Transthoracic echocardiography and a cardiopulmonary exercise test were performed before and after the exercise training programme., Results: Fifty patients (mean±standard deviation [SD] age: 50±13 years) were included a mean of 13.6±12.0 days after aortic valve repair. The preoperative degree of aortic insufficiency was moderate to severe in 35 patients (70%) and the aortic valve was bicuspid in 24 patients (48%). Valve-sparing root replacement and isolated aortic valve repair (including 10% supracoronary aorta replacement) were performed in 64% and 36% of patients, respectively. We found no aortic insufficiency occurrence or worsening and no adverse clinical events after the exercise training programme. Mean left ventricular ejection fraction increased significantly (from 54%±8% to 57%±9%; P=0.0007). Mean peak oxygen consumption and first ventilatory threshold increased from 17.0±5.3 to 22.5±7.8mL/kg/min (32% increase) and from 12.0±3.9 to 14.3±5.2mL/kg/min (19% increase), respectively (both P<0.05)., Conclusion: Exercise training early after aortic valve repair is safe and seems to significantly improve exercise capacity., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

Background/aims: Apelin and its G protein-coupled receptor APJ (gene symbol Aplnr) are strongly expressed in magnocellular vasopressinergic neurons suggesting that the apelin/APJ system plays a key role at the central level in regulating salt and water balance by counteracting the antiduretic action of vasopressin (AVP). Likewise, recent studies revealed that apelin exerts opposite effects to those of vasopressin induced on water reabsorption via a direct action on the kidney collecting duct. However, the underlying mechanisms of the peripheral action of apelin are not clearly understood. Here, we thus investigated the role of the apelin/APJ system in the regulation of water balance in the kidney, and more specifically its involvement in modulating the function of aquaporin-2 (AQP2) in the collecting duct., Methods: Mouse cortical collecting duct cells (mpkCCD) were incubated in the presence of dDAVP and treated with or without apelin-13. Changes in AQP2 expression and localization were determined by immunoblotting and confocal immunofluorescence staining., Results: Herein, we showed that the APJ was present in mpkCCD cells. Treatment of mpkCCD with apelin-13 reduced the cAMP production and antagonized the AVP-induced increase in AQP2 mRNA and protein expressions. Immunofluorescent experiments also revealed that the AVP-induced apical cell surface expression of AQP2, and notably its phosphorylated isoform AQP2-pS269, was considerably reduced following apelin-13 application to mpkCCD cells., Conclusion: Our data reinforce the aquaretic role of the apelin/APJ system in the fine regulation of body fluid homeostasis at the kidney level and its physiological opposite action to the antiduretic activity of AVP., Competing Interests: The authors declare that they have no conflicts of interest with the contents of this article., (© Copyright by the Author(s). Published by Cell Physiol Biochem Press.)

Aims: Brugada syndrome (BrS) is a rare heritable ventricular arrhythmia. Genetic defects in SCN5A, a gene that encodes the α-subunit of the sodium ion channel Nav1.5, are present in 15-30% of BrS cases. SCN5A remains by far, the highest yielding gene for BrS. We studied a young male who presented with syncope at age 11. This proband was screened for possible disease causing SCN5A mutations. The inheritance pattern was also examined amongst his first-degree family members., Methods and Results: The proband had a baseline electrocardiogram that showed Type 2 BrS changes, which escalated to a characteristic Type I BrS pattern during a treadmill test before polymorphic ventricular tachycardia onset at a cycle length of 250 ms. Mutational analysis across all 29 exons in SCN5A of the proband and first-degree relatives of the family revealed that the proband inherited a compound heterozygote mutation in SCN5A, specifically p.A226V and p.R1629X from each parent. To further elucidate the functional changes arising through these mutations, patch-clamp electrophysiology was performed in TSA201 cells expressing the mutated SCN5A channels. The p.A226V mutation significantly reduced peak sodium current (INa) to 24% of wild type (WT) whereas the p.R1629X mutation abolished the current. To mimic the functional state in our proband, functional expression of the compound variants A226V + R1629X resulted in overall peak INa of only 13% of WT (P < 0.01)., Conclusion: Our study is the first to report a SCN5A compound heterozygote in a Singaporean Chinese family. Only the proband carrying both mutations displayed the BrS phenotype, thus providing insights into the expression and penetrance of BrS in an Asian setting., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2015. For permissions please email: journals.permissions@oup.com.)

Background: Arrhythmias associated with QT prolongation on the ECG often lead to sudden unexpected death in epilepsy. The mechanism causing a prolongation of the QT interval during epilepsy remains unknown. Based on observations showing an upregulation of neuronal sodium channels in the brain during epilepsy, we tested the hypothesis that a similar phenomenon occurs in the heart and contributes to QT prolongation by altering cardiac sodium current properties (INa)., Methods and Results: We used the patch clamp technique to assess the effects of epilepsy on the cardiac action potential and INa in rat ventricular myocytes. Consistent with QT prolongation, epileptic rats had longer ventricular action potential durations attributable to a sustained component of INa (INaL). The increase in INaL was because of a larger contribution of neuronal Na channels characterized by their high sensitivity to tetrodotoxin. As in the brain, epilepsy was associated with an enhanced expression of the neuronal isoform NaV1.1 in cardiomyocyte. Epilepsy was also associated with a lower INa activation threshold resulting in increased cell excitability., Conclusions: This is the first study correlating increased expression of neuronal sodium channels within the heart to epilepsy-related cardiac arrhythmias. This represents a new paradigm in our understanding of cardiac complications related to epilepsy., (© 2015 American Heart Association, Inc.)

Background: Functional alterations in the properties of Aβ afferent fibers may account for the increased pain sensitivity observed under peripheral chronic inflammation. Among the voltage-gated sodium channels involved in the pathophysiology of pain, Na(v)1.8 has been shown to participate in the peripheral sensitization of nociceptors. However, to date, there is no evidence for a role of Na(v)1.8 in controlling Aβ-fiber excitability following persistent inflammation., Methods: Distribution and expression of Na(v)1.8 in dorsal root ganglia and sciatic nerves were qualitatively or quantitatively assessed by immunohistochemical staining and by real time-polymerase chain reaction at different time points following complete Freund's adjuvant (CFA) administration. Using a whole-cell patch-clamp configuration, we further determined both total INa and TTX-R Na(v)1.8 currents in large-soma dorsal root ganglia (DRG) neurons isolated from sham or CFA-treated rats. Finally, we analyzed the effects of ambroxol, a Na(v)1.8-preferring blocker on the electrophysiological properties of Nav1.8 currents and on the mechanical sensitivity and inflammation of the hind paw in CFA-treated rats., Results: Our findings revealed that Na(v)1.8 is up-regulated in NF200-positive large sensory neurons and is subsequently anterogradely transported from the DRG cell bodies along the axons toward the periphery after CFA-induced inflammation. We also demonstrated that both total INa and Na(v)1.8 peak current densities are enhanced in inflamed large myelinated Aβ-fiber neurons. Persistent inflammation leading to nociception also induced time-dependent changes in Aβ-fiber neuron excitability by shifting the voltage-dependent activation of Na(v)1.8 in the hyperpolarizing direction, thus decreasing the current threshold for triggering action potentials. Finally, we found that ambroxol significantly reduces the potentiation of Na(v)1.8 currents in Aβ-fiber neurons observed following intraplantar CFA injection and concomitantly blocks CFA-induced mechanical allodynia, suggesting that Na(v)1.8 regulation in Aβ-fibers contributes to inflammatory pain., Conclusions: Collectively, these findings support a key role for Na(v)1.8 in controlling the excitability of Aβ-fibers and its potential contribution to the development of mechanical allodynia under persistent inflammation.

Clinical and animal studies indicate that increased fatty acid delivery to lean tissues induces cardiac electrical remodeling and alterations of cellular calcium homeostasis. Since this may represent a mechanism initiating cardiac dysfunction during establishment of insulin resistance and diabetes or anaerobic cardiac metabolism (ischemia), we sought to determine if short-term exposure to high plasma concentration of fatty acid in vivo was sufficient to alter the cardiac sodium current (INa) in dog ventricular myocytes. Our results show that delivery of triglycerides and nonesterified fatty acids by infusion of Intralipid + heparin (IH) for 8 h increased the amplitude of INa by 43% and shifted its activation threshold by -5 mV, closer to the resting membrane potential. Steady-state inactivation (availability) of the channels was reduced by IH with no changes in recovery from inactivation. As a consequence, INa "window" current, a strong determinant of intracellular Na+ and Ca2+ concentrations, was significantly increased. The results indicate that increased circulating fatty acids alter INa gating in manners consistent with an increased cardiac excitability and augmentation of intracellular calcium. Moreover, these changes could still be measured after the dogs were left to recover for 12 h after IH perfusion, suggesting lasting changes in INa. Our results indicate that fatty acids rapidly induce cardiac remodeling and suggest that this process may be involved in the development of cardiac dysfunctions associated to insulin resistance and diabetes.

Introduction: Neuropeptides arginine-vasopressin (AVP), apelin (APL), and stromal-derived factor-1α (SDF-1α) are involved in the dysfunction of the corticotropic axis observed in septic ICU patients. Study aims were: (i) to portray a distinctive stress-related neuro-corticotropic systemic profile of early sepsis, (ii) to propose a combination data score, for aiding ICU physicians in diagnosing sepsis on admission., Methods: This prospective one-center observational study was carried out in a medical intensive care unit (MICU), tertiary teaching hospital. Seventy-four out of 112 critically ill patients exhibiting systemic inflammatory response syndrome (SIRS) were divided into two groups: proven sepsis and non sepsis, based on post hoc analysis of microbiological criteria and final diagnosis, and compared to healthy volunteers (n = 14). A single blood sampling was performed on admission for measurements of AVP, copeptin, APL, SDF-1α, adrenocorticotropic hormone (ACTH), cortisol baseline and post-stimulation, and procalcitonin (PCT)., Results: Blood baseline ACTH/cortisol ratio was lower and copeptin higher in septic vs. nonseptic patients. SDF-1α was further increased in septic patients vs. normal patients. Cortisol baseline, ACTH, PCT, APACHE II and sepsis scores, and shock on admission, were independent predictors of sepsis diagnosis upon admission. Using the three first aforementioned categorical bio-parameters, a probability score for predicting sepsis yielded an area under the Receiver Operating Curve (ROC) curves better than sepsis score or PCT alone (0.903 vs 0.727 and 0.726: P = 0.005 and P < 0.04, respectively)., Conclusions: The stress response of early admitted ICU patients is different in septic vs. non-septic conditions. A proposed combination of variable score analyses will tentatively help in refining bedside diagnostic tools to efficiently diagnose sepsis after further validation.

Aims: Women have a higher incidence of long QT-related arrhythmias, whereas men exhibit a higher incidence of Brugada syndrome (BrS). The cardiac sodium current (I(Na)) is associated with arrhythmias in BrS and long QT-syndrome (LQTS) and conduction disease. Although a great deal of work has been performed to explain how heterogeneous distribution of repolarizing currents triggers arrhythmias, the transmural distribution of I(Na) within the cardiac ventricle and its contribution to generate the arrhythmogenic substrate remain unknown. We undertook to determine whether I(Na) was heterogeneously distributed within the ventricular wall of canine heart, an animal model close to humans., Methods and Results: Using patch-clamp and molecular biology techniques, we tested whether gender differences exist in the ventricular distribution and amplitude of I(Na) in the canine heart model. Our results show that the I(Na) amplitude is smaller in the female epicardial and endocardial layers of the left ventricle, but similar to male in the mid-myocardium. Exposure of female cardiomyocytes to testosterone increased the amplitude of I(Na) to levels similar to male in epicardium, but had no effects in mid-myocardial and endocardial cells. Castrated male dogs displayed I(Na) amplitudes similar to what was found in female hearts., Conclusion: The larger dispersion of I(Na) amplitude within the female cardiac ventricle may contribute to the higher risk of arrhythmias in females. Testosterone modulates this dispersion. By decreasing the transmural dispersion of I(Na), testosterone may exert a protective effect against LQTS-related arrhythmias in males.

Brugada syndrome has been linked to mutations in SCN5A. Agents that dissociate slowly from the sodium channel such as flecainide and ajmaline unmask the Brugada syndrome electrocardiogram and precipitate ventricular tachycardia/fibrillation. Lidocaine, an agent with rapid dissociation kinetics, has previously been shown to exert no effect in patients with Brugada syndrome. We characterized a novel double mutation of SCN5A (V232I in DI-S4+L1308F in DIII-S4) identified in a rare case of lidocaine (1 mg/kg)-induced Brugada syndrome. We studied lidocaine blockade of I(Na) generated by wild-type and V232I+L1308F mutant cardiac sodium channels expressed in mammalian TSA201 cells using patch clamp techniques. Despite no significant difference in steady-state gating parameters between V232I+L1308F and wild-type sodium currents at baseline, use-dependent inhibition of I(Na) by lidocaine was more pronounced in V232I+L1308F versus wild-type (73.0+/-0.1% versus 18.23+/-0.04% at 10 micromol/L measured at 10 Hz, respectively). A dose of 10 micromol/L lidocaine also caused a more negative shift of steady-state inactivation in V232I+L1308F versus wild-type (-14.1+/-0.3 mV and -4.8+/-0.3 mV, respectively). The individual mutations produced a much less accentuated effect. We report the first case of lidocaine-induced Brugada electrocardiogram phenotype. The double mutation in SCN5A, V232I, and L1308F alters the affinity of the cardiac sodium channel for lidocaine such that the drug assumes Class IC characteristics with potent use-dependent block of the sodium channel. Our results demonstrate an additive effect of the 2 missense mutations to sensitize the sodium channel to lidocaine. These findings suggest caution when treating patients carrying such genetic variations with Class I antiarrhythmic drugs.

Transient receptor potential canonical (TRPC) channels are associated with calcium entry activity in nonexcitable cells. TRPCs can form homo- or heterotetrameric channels, in which case they can assemble together within a subfamily groups. TRPC1, 4, and 5 represent one group, and TRPC3, 6, and 7 represent the other. The molecular determinants involved in promoting subunit tetramerization are not known. To identify them, we generated chimeras by swapping the different domains of TRPC4 with the same regions in TRPC6. We showed that TRPC4 coimmunoprecipitated with the chimeras containing the ankyrin repeats and coiled-coil domains of TRPC4 into TRPC6. However, chimeras containing only the ankyrin repeats or only the coiled-coil domain of TRPC4 did not coimmunoprecipitate with TRPC4. We also showed that a second domain of interaction composed of the pore region and the C-terminal tail is involved in the oligomerization of TRPC4. However, chimeras containing only the pore region or only the C-terminal tail of TRPC4 did not coimmunoprecipitate with TRPC4. Furthermore, we showed that the N terminus of TRPC6 coimmunoprecipitated with the C terminus of TRPC6. Overexpression in HEK293T cells of chimeras that contained an N terminus and a C terminus from different subfamily groups increased intracellular calcium entry subsequent to stimulation of G(q) protein-coupled receptors. These results suggest that two types of interactions are involved in the assembly of the four subunits of the TRPC channel. The first interaction occurs between the N termini and involves two regions. The second interaction occurs between the N terminus and the C terminus and does not appear to be necessary for the activity of TRPCs.

Chronic hypertension is a well established risk factor for the development of cardiovascular disease; however, its prognostic significance after a non-ST-segment elevation acute coronary syndrome remains to be established. Data from 15,414 patients included in six randomized Thrombolysis in Myocardial Infarction (TIMI) trials (TIMI 3B, TIMI 11A, TIMI 11B, TIMI 12, the Orbofiban in Patients With Unstable Coronary Syndromes [OPUS]-TIMI 16, and the Treat Angina With Aggrastat and Determine Cost of Therapy With an Invasive or Conservative Strategy [TACTICS]-TIMI 18) were analyzed. A history of hypertension was present in 10,998 (71.35%) patients; comorbidities and higher TIMI risk scores were more likely in these patients. However, positive troponin and ST-segment deviations were less frequent among hypertensive patients. After multivariate analysis, the history of hypertension was associated with more adverse outcomes, specifically the composite end point of death/myocardial infarction at 30 days and 1 year (odds ratio [OR] 1.54, 95% confidence interval [CI] 1.31-1.81; p<0.001 at 1 year) than in patients without this history. An independent relationship was also observed with mortality (OR 1.70, 95% CI 1.34-2.16; p<0.001 at 1 year), myocardial infarction (OR 1.50, 95% CI 1.23-1.82; p<0.001 at 1 year), recurrent ischemia (OR 1.24, 95% CI 1.11-1.38; p<0.001 at 1 year), and major bleeding (OR 1.45, 95% CI 1.03-2.06; p=0.036 at 30 days). It was concluded that chronic hypertension remains an independent marker for major short- and long-term cardiac adverse outcomes after non-ST-segment elevation acute coronary syndrome.

The QT interval on an electrocardiogram signifies the time required for the heart to repolarize after depolarization. It has long been appreciated that a long QT interval predisposes patients to life-threatening ventricular arrhythmia. Short QT syndrome is a newly described disease characterized by a shortened QT interval and by episodes of syncope, paroxysmal atrial fibrillation or life-threatening cardiac arrhythmias. The syndrome usually affects young and healthy people with no structural heart disease and may be present in sporadic cases as well as in families. Our understanding of a new disease has rarely benefitted so quickly from research in genetics, molecular biology and biophysics. It was first described in 2000 in a handful of patients, and since then 3 different genes associated with the disease and the biophysical basis have been described, and therapy has been made available. Here we review the current understanding of the pathophysiology, clinical presentation and treatment of short QT syndrome.

Objective: Short QT syndrome (SQTS) is characterized by ventricular arrhythmias and sudden death. One form of SQTS is caused by mutation N588K in human ether-a-go-go-related gene (HERG). In this study we sought to determine the potential role of N588K in arrhythmias., Methods: We measured the characteristics of HERG current generated by wild-type (WT) KCNH2 and the N588K mutant channel expressed in mammalian TSA201 cells., Results: Whole-cell patch-clamp recordings of WT HERG currents showed the usual rapid onset of inactivation (rectification) at potentials more positive than +10 mV. In contrast, N588K currents rectified at potentials over +80 mV. Over the physiological range of potentials, N588K currents do not inactivate. During an action potential clamp, WT currents displayed a "hump" like waveform with slow activation kinetics and a rapid increase during phase 3 repolarization. In contrast, N588K currents were proportional to the amplitude of the action potential and displayed a dome-like configuration and a much larger current during the initial phases in the ventricle. Purkinje cell action potentials display a more negative phase 2 repolarization than the ventricle and elicited much smaller WT and N588K currents of similar amplitudes., Conclusions: Physiologically the N588K mutation abolishes rectification of HERG currents and specifically increases I(Kr) in the ventricle with minimal effects on the Purkinje fiber action potential duration. Such preferential prolongation may explain the separation of the T and U waves observed in the ECG of SQTS patients and lead to re-excitation of the ventricle endocardium.

In the mammalian heart, a variety of voltage-gated Na(+) channel transcripts and proteins have been detected. However, little quantitative information is available on the abundance of each transcript during development, or the contribution of TTX-sensitive Na(+) channels to the cardiac sodium current (I(Na)). Using competitive and real-time RT-PCR we investigated the transcription of six Na(+) channels (Na(v)1.1-Na(v)1.6) and the beta1 subunit during mouse heart development. Na(v)1.5 was predominantly expressed in the adult heart, whereas the splice variant Na(v)1.5a was the major Na(+) channel isoform in embryonic hearts. The TTX-resistant Na(+) channel transcripts (Na(v)1.5 and Na(v)1.5a) increased 1.7-fold during postnatal development. Transcripts encoding TTX-sensitive Na(+) channels (Na(v)1.1-Na(v)1.4) and the beta1 subunit gradually increased up to fourfold from postnatal day (P)1 to P126, while the Na(v)1.6 transcript level remained low and constant over the same period. In adults, TTX-sensitive channel mRNA accounted for 30-40% of the channel pool in whole-heart preparations (Na(v)1.3 > Na(v)1.4 > Na(v)1.2 >> Na(v)1.1 approximately Na(v)1.6), and 16% in mRNA from isolated cardiomyocytes (Na(v)1.4 > Na(v)1.3 > Na(v)1.2 > Na(v)1.1 > Na(v)1.6). Confocal immunofluorescence on ventricular myocytes suggested that Na(v)1.1 and Na(v)1.2 were localized at the intercalated disks and in the t tubules. Na(v)1.3 labelling predominantly produced a diffuse but strong intracellular signal. Na(v)1.6 fluorescence was detected only along the Z lines. Electrophysiological recordings showed that TTX-sensitive and TTX-resistant Na(+) channels, respectively, accounted for 8% and 92% of the I(Na) in adult ventricular cardiomyocytes. Our data suggest that neuronal and skeletal muscle Na(+) channels contribute to the action potential of cardiomyocytes in the adult mammalian heart.

Objective: To determine the presence and the potential contribution of neuronal sodium channels to dog cardiac function., Methods: We used a combination of electrophysiological (patch clamp), RT-PCR, biochemical and immunohistochemical techniques to identify and localize neuronal Na(+) channels in dog heart and determine their potential contribution to the fast sodium current., Results: In all cardiac tissues investigated, Na(v)1.1, Na(v)1.2 and Na(v)1.3 transcripts were detected. In immunoblots, we found Na(v)1.1 and Na(v)1.2 proteins in the ventricle (V) and in Purkinje fibers (PF). Na(v)1.3 immunoblots suggested strong proteolytic activity against this isoform in the heart. Na(v)1.6 was not found in any of the tissues tested. Confocal immunofluorescence on cardiac myocytes showed that Na(v)1.1 was predominantly localized at the intercalated disks in V and PF and around the nucleus (V). Na(v)1.2 was only present at the Z lines (V). Consistent with the immunoblot data, an intense but diffuse intracellular staining was observed for Na(v)1.3. Na(v)1.6 fluorescence staining was faint and diffuse. Surprisingly, immunoblots indicated the presence of two Na(v)beta 2 variants: a 42-kDa protein that co-localized with Na(v)1.2 at the Z lines in V and a 34-kDa protein that co-localized with Na(v)1.1 at the intercalated disks in PF. In agreement with the biochemical data, electrophysiological results suggest that neuronal sodium channels generate 10+/-5% and 22+/-5% of the peak sodium current in dog ventricle and Purkinje fibers, respectively., Conclusions: Our results suggest that neuronal NaChs are more abundant in Purkinje fibers than in ventricles, and this suggests a role for them in cardiac conduction.

Background: Sudden cardiac death takes the lives of more than 300 000 Americans annually. Malignant ventricular arrhythmias occurring in individuals with structurally normal hearts account for a subgroup of these sudden deaths. The present study describes the genetic basis for a new clinical entity characterized by sudden death and short-QT intervals in the ECG., Methods and Results: Three families with hereditary short-QT syndrome and a high incidence of ventricular arrhythmias and sudden cardiac death were studied. In 2 of them, we identified 2 different missense mutations resulting in the same amino acid change (N588K) in the S5-P loop region of the cardiac IKr channel HERG (KCNH2). The mutations dramatically increase IKr, leading to heterogeneous abbreviation of action potential duration and refractoriness, and reduce the affinity of the channels to IKr blockers., Conclusions: We demonstrate a novel genetic and biophysical mechanism responsible for sudden death in infants, children, and young adults caused by mutations in KCNH2. The occurrence of sudden cardiac death in the first 12 months of life in 2 patients suggests the possibility of a link between KCNH2 gain of function mutations and sudden infant death syndrome. KCNH2 is the binding target for a wide spectrum of cardiac and noncardiac pharmacological compounds. Our findings may provide better understanding of drug interaction with KCNH2 and have implications for diagnosis and therapy of this and other arrhythmogenic diseases.

There are important species-specific differences in K+ current profiles and arrhythmia susceptibility, but interspecies comparisons of K+ channel subunit expression are lacking. We quantified voltage-gated K+ channel (Kv) subunit mRNA and protein in rabbits, guinea pigs, and humans. Kv1.4, Kv4.2, and Kv4.3 mRNA was present in rabbits but undetectable in guinea pigs. MinK mRNA concentration in guinea pigs was almost threefold greater versus humans and 20-fold versus rabbits. MinK protein expression in guinea pigs was almost twofold that in humans and sixfold that in rabbits. KvLQT1 mRNA concentration was greatest in humans, and protein expression in humans was increased by approximately 2- and approximately 7-fold compared with values in rabbits and guinea pigs, respectively. The ether-a-go-go-related gene (ERG1) mRNA was more concentrated in humans, but ERG1 protein expression could not be compared across species because of epitope sequence differences. We conclude that important interspecies differences in cardiac K+ channel subunit expression exist and may contribute to the following: 1) lack of a transient outward current in the guinea pig (alpha-subunit transcription absent in the guinea pig heart); 2) small slow delayed rectifier current and torsades de pointes susceptibility in the rabbit (low-level minK expression); and 3) large slow component of the delayed rectifier current in the guinea pig (strong minK expression).

Objective: In animal models of hypertrophy, electrical remodeling giving rise to QT prolongation occurs rapidly and is associated with the development of torsade de pointes (TdP) arrhythmias and sudden death. Chronic AV block (CAVB)-induced hypertrophy in dogs has been associated with a reduction in the slow component (I(Ks)) of the delayed rectifier potassium current (I(K)), which contributes to a prolongation of ventricular repolarization, the development of an acquired form of long QT, and the substrate for triggered activity and TdP. The present study was designed to probe the molecular basis for the decrease in I(Ks) by studying the characteristics of KCNE1 and KCNQ1, the putative genes responsible for formation of the channel., Methods and Results: Using a combination of Northern blot, competitive multiplex PCR and immunoblot assays, we found that CAVB reduces KCNE1 and KCNQ1 RNA in the canine ventricles by 70 and 80%, respectively. Protein levels of KCNE1 and KCNQ1 were reduced by 60 and 50%, respectively. We also demonstrate at the molecular level the basis for inter-ventricular difference in I(Ks) density previously reported in hearts of normal dogs and show the basis for reduction of this difference in the CAVB dog., Conclusions: Our results indicate that the CAVB-induced reduction in I(Ks) is due to a down-regulation of KCNE1 and KCNQ1 transcription. The data suggest that electrical remodeling of the cardiac ventricle during hypertrophy involves regulation of the gene expression through modulation of transcriptional and translational regulatory pathways. The reduction in KCNE1 and KCNQ1 expression increases the dependence of ventricular repolarization on the rapid component of I(K) and may potentiate the action of Class III antiarrhythmic agents.

The repolarization phase of the cardiac action potential is dependent on transmembrane K(+) currents. The slow (I(Ks)) and fast (I(Kr)) components of the delayed-rectifier cardiac K(+) current are generated by pore-forming alpha subunits KCNQ1 and KCNH2, respectively, in association with regulatory beta-subunit KCNE1, KCNE2 and perphaps KCNE3. In the present study we have investigated the distribution of transcripts encoding these five potassium channel-forming subunits during mouse heart development as well as the protein distribution of KCNQ1 and KCNH2. KCNQ1 and KCNH2 mRNAs (and protein) are first expressed at embryonic day (E) 9.5, showing comparable levels of expression within the atrial and ventricular myocardium during the embryonic and fetal stages. In contrast, the beta-subunits display a more dynamic pattern of expression during development. KCNE1 expression is first observed at E9.5 throughout the entire myocardium and progressively is confined to the ventricular myocardium. With further development (E16.5), KCNE1 expression is mainly confined to the compact ventricular myocardium. KCNE2 is first expressed at E9.5 and it is restricted already to the atrial myocardium. KCNE3 is first expressed at E8.5 throughout the myocardium and with further development, it becomes restricted to the atrial myocardium. The fact that alpha subunits are homogeneously distributed within the myocardium, whereas the beta subunits display a regionalized expression profile during cardiac development, suggest that differences in the slow and fast component of the delayed-rectifier cardiac K(+) currents between the atrial and the ventricular cardiomyocytes are mainly determined by differential beta-subunit distribution.

The Brugada syndrome is a major cause of sudden death, particularly among young men of Southeast Asian and Japanese origin. The syndrome is characterized electrocardiographically by an ST-segment elevation in V1 through V3 and a rapid polymorphic ventricular tachycardia that can degenerate into ventricular fibrillation. Our group recently linked the disease to mutations in SCN5A, the gene encoding for the alpha subunit of the cardiac sodium channel. When heterologously expressed in frog oocytes, electrophysiological data recorded from the Thr1620Met missense mutant failed to adequately explain the electrocardiographic phenotype. Therefore, we sought to further characterize the electrophysiology of this mutant. We hypothesized that at more physiological temperatures, the missense mutation may change the gating of the sodium channel such that the net outward current is dramatically augmented during the early phases of the right ventricular action potential. In the present study, we test this hypothesis by expressing Thr1620Met in a mammalian cell line, using the patch-clamp technique to study the currents at 32 degrees C. Our results indicate that Thr1620Met current decay kinetics are faster when compared with the wild type at 32 degrees C. Recovery from inactivation was slower for Thr1620Met at 32 degrees C, and steady-state activation was significantly shifted. Our findings explain the features of the ECG of Brugada patients, illustrate for the first time a cardiac sodium channel mutation of which the arrhythmogenicity is revealed only at temperatures approaching the physiological range, and suggest that some patients may be more at risk during febrile states.

Background: Administration of the antihistamine terfenadine (Seldane) to patients may result in acquired long QT syndrome and ventricular arrhythmias. One human cardiac target is Kv1.5, which expresses the ultrarapid outward K+ current (Ikur) in atrium but may play only a minor role in ventricle. Another possible target is HERG, the human ether-a-go-go-related gene that expresses a delayed rectifier current (IKr) in human ventricle and produces hereditary long QT syndrome when defective., Methods and Results: We therefore heterologously expressed Kv1.5 and HERG in Xenopus oocytes to compare the sensitivity of each to terfenadine. We found that HERG was 10 times more sensitive than Kv1.5 to terfenadine block. The apparent Kd values for HERG and Kv1.5 currents were 350 nmol/L and 2.7 mumol/L, respectively. These Kd values compare well with values reported for terfenadine block of IKr and IKur currents in human atrial myocytes. The Kd value for HERG block is relevant to the toxicity of the antihistamine, since the clinical terfenadine concentrations in human plasma may reach the 100 nmol/L range., Conclusions: Terfenadine carboxylate, the major metabolite of terfenadine, does not block either HERG or Kv1.5, which agrees with the hypothesis that the buildup of parent terfenadine is the likely explanation for its cardiotoxicity. We propose that the blocking of HERG by terfenadine explains the acquired long QT syndrome. HERG is likely to be the primary target for the known cardiotoxic effects of other, related antihistamines.

Inheritable long-QT syndrome (LQTS) is a disease in which delayed ventricular repolarization leads to cardiac arrhythmias and the possibility of sudden death. In the chromosome 3-linked disease, one mutation of the cardiac Na+ channel gene results in a deletion of residues 1505 to 1507 (Delta KPQ), and two mutation result in substitutions (N1325S and R1644H). We compared all three mutant-channel phenotypes by heterologous expression in Xenopus oocytes. Each produced a late phase of inactivation-resistant, mexiletine- and tetrodotoxin-sensitive whole-cell currents, but the underlying mechanisms were different at the single-channel level. N1325S and R1644H showed dispersed reopenings after the initial transient, whereas Delta KPQ showed both dispersed reopenings and long-lasting bursts. Thus, two distinct biophysical defects underlie the in vitro phenotype of persistent current in Na+ channel-linked LQTS, and the additive effects of both are responsible for making the Delta KPQ phenotype the most severe.