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BackgroundThe coronavirus disease (COVID-19) pandemic, caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in the self-quarantine of countless people due to possible infection. This situation makes telemedicine necessary as it can overcome geographical barriers, increase the number of people served, and provide online clinical support for patients. However, the outcomes of telemedicine have not yet been evaluated. ObjectiveThe aim of our study is to describe the epidemiological features and clinical symptoms of patients receiving remote diagnosis and treatment at the online outpatient clinic of our hospital, as well as to analyze the outcomes and advantages of telemedicine, during the COVID-19 pandemic. MethodsData from patients receiving remote diagnosis and treatment via consultation services for COVID-19 concerns at the online outpatient clinic of Henan Provincial People's Hospital from January 24 to February 17, 2020, were collected. A retrospective analysis was performed on epidemiological features, clinical symptoms, and preliminary outcomes. ResultsOnline inquiry, consultation, and suggestions were provided for patient concerns related to COVID-19. Our hospital also offered offline noncontact drug delivery services following online ordering and payment. A total of 4589 patients receiving remote diagnosis and treatment were recruited. The daily number of online outpatient visits initially increased and then decreased, reaching its peak on January 28 when the daily number of online outpatient visits totaled 612. Of 4589 patients, 1940 (42.3%) were males and 2649 (57.7%) were females (age range: 78 days to 85 years). Most patients were aged 20-39 years (n=3714, 80.9%) and came from Henan Province (n=3898, 84.9%). The number of patients from other provinces was 691 (15.1%). During the online consultations, patients discussed the following symptoms: fever (n=2383), cough (n=1740), nasal obstruction (n=794), fatigue (n=503), and diarrhea (n=276). A total of 873 orders of noncontact drug delivery following online payment was completed. The daily number of such orders gradually stabilized after the initial, steady increase. For offline drug delivery orders, the median (IQR) was 36 (58). An online satisfaction survey was filled out postconsultation by patients; of the 985 responses received, 98.1% (n=966) of respondents were satisfied with the service they received. ConclusionsRemote diagnosis and treatment offered via online outpatient consultations effectively reduced the burden on hospitals, prevented overcrowding, reduced the risk of cross-infection, and relieved patients' anxiety during the COVID-19 outbreak. This plays an essential role in pandemic management.

Ischemic stroke is a devastating disease that affects millions of patients worldwide. Unfortunately, there are no effective medications for mitigating brain injury after ischemic stroke. TRP channels are evolutionally ancient biosensors that detect external stimuli as well as tissue or cellular injury. To date, many members of the TRP superfamily have been reported to contribute to ischemic brain injury, including the TRPC subfamily (1, 3, 4, 5, 6, 7), TRPV subfamily (1, 2, 3, 4) and TRPM subfamily (2, 4, 7). These TRP channels share structural similarities but have distinct channel functions and properties. Their activation during ischemic stroke can be beneficial, detrimental, or even both. In this review, we focus on discussing the interesting features of stroke-related TRP channels and summarizing the underlying cellular and molecular mechanisms responsible for their involvement in ischemic brain injury. [ABSTRACT FROM AUTHOR]

As the leading cause of mortality worldwide, cardiovascular disease (CVD) represents a variety of heart diseases and vascular disorders, including atherosclerosis, aneurysm, ischemic injury in the heart and brain, arrythmias, and heart failure. Macrophages, a diverse population of immune cells that can promote or suppress inflammation, have been increasingly recognized as a key regulator in various processes in both healthy and disease states. In healthy conditions, these cells promote the proper clearance of cellular debris, dead and dying cells, and provide a strong innate immune barrier to foreign pathogens. However, macrophages can play a detrimental role in the progression of disease as well, particularly those inflammatory in nature. This review will focus on the current knowledge regarding the role of macrophages in cardiovascular diseases. [ABSTRACT FROM AUTHOR]

Background: Eukaryotic genes contain introns that are removed by the spliceosomal machinery during mRNA maturation. Introns impose a huge energetic burden on a cell; therefore, they must play an essential role in maintaining genome stability and/or regulating gene expression. Many genes (> 50%) in Plasmodium parasites contain predicted introns, including introns in 5′ and 3′ untranslated regions (UTR). However, the roles of UTR introns in the gene expression of malaria parasites remain unknown. Methods: In this study, an episomal dual-luciferase assay was developed to evaluate gene expression driven by promoters with or without a 5′UTR intron from four Plasmodium yoelii genes. To investigate the effect of the 5′UTR intron on endogenous gene expression, the pytctp gene was tagged with 3xHA at the N-terminal of the coding region, and parasites with or without the 5′UTR intron were generated using the CRISPR/Cas9 system. Results: We showed that promoters with 5′UTR introns had higher activities in driving gene expression than those without 5′UTR introns. The results were confirmed in recombinant parasites expressing an HA-tagged gene (pytctp) driven by promoter with or without 5′UTR intron. The enhancement of gene expression was intron size dependent, but not the DNA sequence, e.g. the longer the intron, the higher levels of expression. Similar results were observed when a promoter from one strain of P. yoelii was introduced into different parasite strains. Finally, the 5′UTR introns were alternatively spliced in different parasite development stages, suggesting an active mechanism employed by the parasites to regulate gene expression in various developmental stages. Conclusions: Plasmodium 5′UTR introns enhance gene expression in a size-dependent manner; the presence of alternatively spliced mRNAs in different parasite developmental stages suggests that alternative slicing of 5′UTR introns is one of the key mechanisms in regulating parasite gene expression and differentiation. [ABSTRACT FROM AUTHOR]

Aims Damage of the blood–brain barrier (BBB) is a hallmark of brain injury during the early stages of ischemic stroke. The subsequent endothelial hyperpermeability drives the initial pathological changes and aggravates neuronal death. Transient receptor potential melastatin 2 (TRPM2) is a Ca2+-permeable nonselective cation channel activated by oxidative stress. However, whether TRPM2 is involved in BBB degradation during ischemic stroke remains unknown. We aimed to investigate the role of TRPM2 in BBB degradation during ischemic stroke and the underlying molecular mechanisms. Methods and results Specific deletion of Trpm2 in endothelial cells using Cdh5 Cre produces a potent protective effect against brain injury in mice subjected to middle cerebral artery occlusion (MCAO), which is characterized by reduced infarction size, mitigated plasma extravasation, suppressed immune cell invasion, and inhibited oxidative stress. In vitro experiments using cultured cerebral endothelial cells (CECs) demonstrated that either Trpm2 deletion or inhibition of TRPM2 activation attenuates oxidative stress, Ca2+ overload, and endothelial hyperpermeability induced by oxygen–glucose deprivation (OGD) and CD36 ligand thrombospondin-1 (TSP1). In transfected HEK293T cells, OGD and TSP1 activate TRPM2 in a CD36-dependent manner. Noticeably, in cultured CECs, deleting Trpm2 or inhibiting TRPM2 activation also suppresses the activation of CD36 and cellular dysfunction induced by OGD or TSP1. Conclusions In conclusion, our data reveal a novel molecular mechanism in which TRPM2 and CD36 promote the activation of each other, which exacerbates endothelial dysfunction during ischemic stroke. Our study suggests that TRPM2 in endothelial cells is a promising target for developing more effective and safer therapies for ischemic stroke. [ABSTRACT FROM AUTHOR]

Toxic Chinese materia medica (CMM) has both pharmacological activities and toxic effects. Based on thousands of years of experience in the application of CMMs, people have explored many practical processing methods of CMMs, also known as "Pao Zhi", to reduce/control toxicity and preserve/enhance efficacy. Toxic CMMs have been used throughout China's hospitals. Yet, the production and use of toxic CMM should be carried out in accordance with the Chinese pharmacopoeia (ChP) and the processing regulations formulated by the health administrative departments of provinces, autonomous regions, and municipalities directly under the Central Government. This paper summarizes the current understanding and awareness of toxicity and 45 toxic CMMs, the commonly used processing methods of toxic CMMs recorded in the 2020 edition of ChP, and the changes in the chemical component, toxicity, or efficacy profiles after processing. This review may provide useful information for the processing methods of toxic CMMs worldwide. We believe that with an in-depth study and understanding of toxic CMMs combined with a standardized application, the toxicity of CMMs will be predictable and controllable in the future. [ABSTRACT FROM AUTHOR]

TRPM2 is a [Ca.sup.2+]-permeable nonselective cation channel that plays important roles in oxidative stress-mediated cell death and inflammation processes. However, how TRPM2 is regulated under physiological and pathological conditions is not fully understood. Here, we report that both intracellular and extracellular protons block TRPM2 by inhibiting channel gating. We demonstrate that external protons block TRPM2 with an [IC.sub.50] of p[H.sub.o] = 5.3, whereas internal protons inhibit TRPM2 with an [IC.sub.50] of p[H.sub.i] = 6.7. Extracellular protons inhibit TRPM2 by decreasing single-channel conductance. We identify three titratable residues, H958, D964, and E994, at the outer vestibule of the channel pore that are responsible for p[H.sub.o] sensitivity. Mutations of these residues reduce single-channel conductance, decrease external [Ca.sup.2+] ([[[Ca.sup.2+]].sub.o]) affinity, and inhibit [[[Ca.sup.2+]].sub.o]-mediated TRPM2 gating. These results support the following model: titration of H958, D964, and E994 by external protons inhibits TRPM2 gating by causing conformation change of the channel, and/or by decreasing local [Ca.sup.2+] concentration at the outer vestibule, therefore reducing [[[Ca.sup.2+]].sub.o] permeation and inhibiting [[[Ca.sup.2+]].sub.o]-mediated TRPM2 gating. We find that intracellular protons inhibit TRPM2 by inducing channel closure without changing channel conductance. We identify that D933 located at the C terminus of the $4-$5 linker is responsible for intracellular pH sensitivity. Replacement of [Asp.sup.933] by [Asn.sup.933] changes the [IC.sub.50] from p[H.sub.i] = 6.7 to p[H.sub.i] = 5.5. Moreover, substitution of [Asp.sup.933] with various residues produces marked changes in proton sensitivity, intracellular ADP ribose/[Ca.sup.2+] sensitivity, and gating profiles of TRPM2. These results indicate that D933 is not only essential for intracellular pH sensitivity, but it is also crucial for TRPM2 channel gating. Collectively, our findings provide a novel mechanism for TRPM2 modulation as well as molecular determinants for pH regulation of TRPM2. Inhibition of TRPM2 by acidic pH may represent an endogenous mechanism governing TRPM2 gating and its physiological/pathological functions. doi/ 10.1085/jgp.200910254

TRPM6 and TRPM7 are two known channel kinases that play important roles in various physiological processes, including [Mg.sup.2+] homeostasis. Mutations in TRPM6 cause hereditary hypomagnesemia and secondary hypocalcemia (HSH). However, whether TRPM6 encodes functional channels is controversial. Here we demonstrate several signature features of TRPM6 that distinguish TRPM6 from TRPM7 and TRPM6/7 channels. We show that heterologous expression of TRPM6 but not the mutant TRPM[6.sup.S141L] produces functional channels with divalent cation permeability profile and pH sensitivity distinctive from those of TRPM7 channels and TRPM6/7 complexes. TRPM6 exhibits unique unitary conductance that is 2- and 1.5-fold bigger than that of TRPM7 and TRPM6/7. Moreover, micromolar levels of 2-aminoethoxydiphenyl borate (2-APB) maximally increase TRPM6 but significantly inhibit TRPM7 channel activities; whereas millimolar concentrations of 2-APB potentiate TRPM6/7 and TRPM7 channel activities. Furthermore, [Mg.sup.2+] and [Ca.sup.2+] entry through TRPM6 is enhanced three- to fourfold by 2-APB. Collectively, these results indicate that TRPM6 forms functional homomeric channels as well as heteromeric TRPM6/7 complexes. The unique characteristics of these three channel types, TRPM6, TRPM7, and TRPM6/7, suggest that they may play different roles in vivo.

TRPM7 is unique in being both an ion channel and a protein kinase. It conducts a large outward current at + 100 mV but a small inward current at voltages ranging from--100 to -40 mV under physiological ionic conditions. Here we show that the small inward current of TRPM7 was dramatically enhanced by a decrease in extracellular pH, with an ~10-fold increase at pH 4.0 and 1-2-fold increase at pH 6.0. Several lines of evidence suggest that protons enhance TRPM7 inward currents by competing with [Ca.sup.2+] and [Mg.sup.2+] for binding sites, thereby releasing blockade of divalent cations on inward monovalent currents. First, extracellular protons significantly increased monovalent cation permeability. Second, higher proton concentrations were required to induce 50% of maximal increase in TRPM7 currents when the external [Ca.sup.2+] and [Mg.sup.2+ concentrations were increased. Third, the apparent] affinity for [Ca.sup.2+] and [Mg.sup.2+] was significantly diminished at elevated external [H.sup.+] concentrations. Fourth, the anomalous-mole fraction behavior of [H.sup.+] permeation further suggests that protons compete with divalent cations for binding sites in the TRPM7 pore. Taken together, it appears that at physiological pH (7.4), [Ca.sup.2+] and [Mg.sup.2+] bind to TRPM7 and inhibit the monovalent cationic currents; whereas at high [H.sup.+] concentrations, the affinity of TRPM7 for [Ca.sup.2+] and [Mg.sup.2+] is decreased, thereby allowing monovalent cations to pass through TRPM7. Furthermore, we showed that the endogenous TRPM7-like current, which is known as [Mg.sup.2+]-inhibitable cation current (MIC) or Mg nucleotide--regulated metal ion current (MagNuM) in rat basophilic leukemia (RBL) cells was also significantly potentiated by acidic pH, suggesting that MIC/MagNuM is encoded by TRPM7. The pH sensitivity represents a novel feature of TRPM7 and implies that TRPM7 may play a role under acidic pathological conditions.

Magnesium is essential for cellular life, but how it is homeostatically controlled still remains poorly understood. Here, we report that members of CNNM family, which have been controversially implicated in both cellular Mg2+ influx and efflux, selectively bind to the TRPM7 channel to stimulate divalent cation entry into cells. Coexpression of CNNMs with the channel markedly increased uptake of divalent cations, which is prevented by an inactivating mutation to the channel's pore. Knockout (KO) of Trpm7 in cells or application of the TRPM7 channel inhibitor NS8593 also interfered with CNNM-stimulated divalent cation uptake. Conversely, KO of CNNM3 and CNNM4 in HEK-293 cells significantly reduced TRPM7-mediated divalent cation entry, without affecting TRPM7 protein expression or its cell surface levels. Furthermore, we found that cellular overexpression of phosphatases of regenerating liver (PRLs), known CNNMs binding partners, stimulated TRPM7-dependent divalent cation entry and that CNNMs were required for this activity. Whole-cell electrophysiological recordings demonstrated that deletion of CNNM3 and CNNM4 from HEK-293 cells interfered with heterologously expressed and native TRPM7 channel function. We conclude that CNNMs employ the TRPM7 channel to mediate divalent cation influx and that CNNMs also possess separate TRPM7-independent Mg2+ efflux activities that contribute to CNNMs' control of cellular Mg2+ homeostasis. Magnesium is essential for cellular life, but how is it homeostatically controlled? This study shows that proteins of the CNNM family bind to the TRPM7 channel to stimulate divalent cation entry into cells, independent of their function in regulating magnesium ion efflux. [ABSTRACT FROM AUTHOR]

The Bacillus halodurans voltage-gated sodium-selective channel (NaChBac) (Ren, D., B. Navarro, H. Xu, L. Yue, Q. Shi, and D.E. Clapham. 200lb. Science. 294:2372-2375), is an ideal candidate for high resolution structural studies because it can be expressed in mammalian cells and its functional properties studied in detail. It has the added advantage of being a single six transmembrane (6TM) orthologue of a single repeat of mammalian voltage-gated [Ca.sup.2+] (Cav) and [Na.sub.+] (Nav) channels. Here we report that six amino acids in the pore domain (LESWAS) participate in the selectivity filter. Replacing the amino acid residues adjacent to glutamatic acid (E) by a negatively charged aspartate (D; LEDWAS) converted the [Na.sub.+]-selective NaChBac to a [Ca.sup.2+]- and [Na.sub.+]-permeant channel. When additional aspartates were incorporated (LDDWAD), the mutant channel resulted in a highly expressing voltage-gated [Ca.sup.2+]-selective conductance. KEY WORDS: bacterial channels * calcium channels * sodium channels * ion/membrane channel

Author(s): Lixia Yue [1]; Ji-Bin Peng [2]; Matthias A. Hediger [2]; David E. Clapham (corresponding author) [1, 3] The calcium-release-activated Ca[sup.2+] channel, I [sub.CRAC] [1, 2, 3], is a highly [...]

Research was conducted to examine the transmural heterogeneity of action potentials and I(sub to1) in myocytes isolated from the human right ventricle. Results reveal that M cells are present in the right ventricle in humans and that a gradient of I(sub to1) is present in cells across the human right ventricular wall from the endocardium to the epicardium. Findings show important transmural heterogeneity in the action potential and I(sub to1) properties pointing to an important clinical implication in human cardiac electrophysiology.

Isolation of cells by chunk and perfusion methods reveals that the transient outward K+ current, (Ito1), Ca2+ dependent Cl- current, (Ito2), and the delayed rectifier K+ current, (Ik), are found in the dog atrium. Ik is more sensitive to the isolation method than Ito1 or Ito2. The properties of Ito1 and Ik repolarizing currents of the dog atrium are similar to those in the human atrium. These studies help in the in vivo and in vitro analysis of canine atrial electrophysiology.

microRNAs have been reported to play important roles in the pathogenesis of rheumatoid arthritis (RA). This study examined the effects of miR-522 on the biological behaviors of RA synovial fibroblasts. The expression levels of miR-522 and relevant genes were measured by quantitative real-time PCR. The protein levels of cytokines were determined by ELISA assay. The protein levels of matrix metalloproteinases (MMPs) and suppressor of cytokine signaling 3 (SOCS3) were determined by western blot assay. Luciferase reporter assay was used to confirm the potential target of miR-522. Our results showed that miR-522 was upregulated in synovial fibroblasts from RA patients, and miR-522 expression level was significantly associated with the RA-associated clinical parameters. miR-522 overexpression increased the mRNA and protein expression levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and MMPs (MMP-1, MMP-3, and MMP-13) in RA synovial fibroblasts. Lipopolysaccharide induced the upregulation of TNF-α, IL-1β, and MMPs in RA synovial fibroblasts, which was reversed by miR-522 knockdown. Bioinformatics analysis identified SOCS3 as a potential target of miR-522, and this target of miR-522 was confirmed by luciferase reporter assay, and miR-522 overexpression suppressed the mRNA and protein expression levels of SOCS3. The enforced expression of SOCS3 attenuated the enhanced effects of miR-522 on mRNA expression levels of TNF-α, IL-1β, and MMPs. Collectively, our results suggested that miR-522 regulated the expression of proinflammatory cytokines and MMPs partly via targeting SOCS3 in RA synovial fibroblasts, which may contribute to pathogenesis of RA. [ABSTRACT FROM AUTHOR]

The vast potential of human induced pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs) in preclinical models of cardiac pathologies, precision medicine, and drug screening remains to be fully realized because hiPSC-CMs are immature without adult-like characteristics. Here, we present a method to accelerate hiPSC-CM maturation on a substrate, cardiac mimetic matrix (CMM), mimicking adult human heart matrix ligand chemistry, rigidity, and submicron ultrastructure, which synergistically mature hiPSC-CMs rapidly within 30 days. hiPSC-CMs matured on CMM exhibit systemic transcriptomic maturation toward an adult heart state, are aligned with high strain energy, metabolically rely on oxidative phosphorylation and fatty acid oxidation, and display enhanced redox handling capability, efficient calcium handling, and electrophysiological features of ventricular myocytes. Endothelin-1-induced pathological hypertrophy is mitigated on CMM, highlighting the role of a native cardiac microenvironment in withstanding hypertrophy progression. CMM is a convenient model for accelerated development of ventricular myocytes manifesting highly specialized cardiac-specific functions. [Display omitted] • Rapid iPSC-CM maturation on surfaces mimicking native cardiac microenvironment • Concurrent metabolic and redox maturation on cardiac mimetic matrix (CMM) • Hybrid Steiner tree network identifies intermediaries involved in cardiac maturation • Cardiac ultrastructure moderates hypertrophic disease phenotype Afzal et al. induce physiologically inspired cardiac maturation. The resulting cardiac constructs display features of ventricular myocytes within 30 days including structural alignment, electrophysiological maturation, molecular signature, mitochondrial energetics and fatty acid oxidation, and efficient oxidative stress handling capability, facilitating their use in disease modeling and preclinical drug screening. [ABSTRACT FROM AUTHOR]

As heart failure due to myocardial infarction remains a leading cause of morbidity worldwide, cell-based cardiac regenerative therapy using cardiac progenitor cells (CPCs) could provide a potential treatment for the repair of injured myocardium. As adult CPCs may have limitations regarding tissue accessibility and proliferative ability, CPCs derived from embryonic stem cells (ESCs) could serve as an unlimited source of cells with high proliferative ability. As one of the CPCs that can be derived from embryonic stem cells, Isl1 expressing cardiac progenitor cells (Isl1-CPCs) may serve as a valuable source of cells for cardiac repair due to their high cardiac differentiation potential and authentic cardiac origin. In order to generate an unlimited number of Isl1-CPCs, we used a previously established an ESC line that allows for isolation of Isl1-CPCs by green fluorescent protein (GFP) expression that is directed by the mef2c gene, specifically expressed in the Isl1 domain of the anterior heart field. To improve the efficiency of cardiac differentiation of Isl1-CPCs, we studied the role of Bmp4 in cardiogenesis of Isl1-CPCs. We show an inductive role of Bmp directly on cardiac progenitors and its enhancement on early cardiac differentiation of CPCs. Upon induction of Bmp4 to Isl1-CPCs during differentiation, the cTnT+ cardiomyocyte population was enhanced 2.8±0.4 fold for Bmp4 treated CPC cultures compared to that detected for vehicle treated cultures. Both Bmp4 treated and untreated cardiomyocytes exhibit proper electrophysiological and calcium signaling properties. In addition, we observed a significant increase in Tbx5 and Tbx20 expression in differentiation cultures treated with Bmp4 compared to the untreated control, suggesting a link between Bmp4 and Tbx genes which may contribute to the enhanced cardiac differentiation in Bmp4 treated cultures. Collectively these findings suggest a cardiomyogenic role for Bmp4 directly on a pure population of Isl1 expressing cardiac progenitors, which could lead to enhancement of cardiac differentiation and engraftment, holding a significant therapeutic value for cardiac repair in the future. [ABSTRACT FROM AUTHOR]

Ischemic stroke causes a heavy health burden worldwide, with over 10 million new cases every year. Despite the high prevalence and mortality rate of ischemic stroke, the underlying molecular mechanisms for the common etiological factors of ischemic stroke and ischemic stroke itself remain unclear, which results in insufficient preventive strategies and ineffective treatments for this devastating disease. In this review, we demonstrate that transient receptor potential cation channel, subfamily M, member 2 (TRPM2), a non-selective ion channel activated by oxidative stress, is actively involved in all the important steps in the etiology and pathology of ischemic stroke. TRPM2 could be a promising target in screening more effective prophylactic strategies and therapeutic medications for ischemic stroke. [ABSTRACT FROM AUTHOR]

TRPM7 (ChaK1, TRP-PLIK, LTRPC7) is a ubiquitous, calcium-permeant ion channel that is unique in being both an ion channel and a serine/threonine kinase. The kinase domain of TRPM7 directly associates with the C2 domain of phospholipase C (PLC). Here, we show that in native cardiac cells and heterologous expression systems, Gαq-linked receptors or tyrosine kinase receptors that activate PLC potently inhibit channel activity. Numerous experimental approaches demonstrated that phosphatidylinositol 4,5-bisphosphate (PIP2), the substrate of PLC, is a key regulator of TRPM7. We conclude that receptor-mediated activation of PLC results in the hydrolysis of localized PIP2, leading to inactivation of the TRPM7 channel. [ABSTRACT FROM AUTHOR]

Objective: A dog atrial ultra-rapid delayed rectifier current (IKur.d) is involved in canine atrial repolarization and shares similarities with the human atrial ultra-rapid delayed rectifier (IKur). Almost no information is available about the actions of antiarrhythmic drugs on IKur.d. This study evaluated effects of ambasilide, quinidine, flecainide and verapamil on IKur.d in isolated canine atrial myocytes. Methods: Standard whole-cell patch clamp techniques were used to study the effects of multiple concentrations of each drug. Results: All drugs produced reversible concentration-, voltage- and time-dependent IKur.d inhibition. Significant effects of quinidine, flecainide and ambasilide were noted at atrial-effective antiarrhythmic concentrations in the dog. Upon the onset of a depolarizing pulse, block developed exponentially in relation to time, with the blocking rate-constant increasing with drug concentration, consistent with open-channel blockade and permitting the calculation of forward and reverse rate-constants. For all drugs, the 50% blocking concentration (EC50) showed significant voltage-dependence, decreasing at more positive potentials. The magnitude of voltage-dependent block was directly related to the degree of drug-induced shift in the voltage dependence of activation (r=0.97), pointing to open-channel block as a mechanism for voltage-dependent action. An additional component of voltage-dependence suggested that blocking sites were subjected to 17–21% of the transmembrane voltage field. Conclusions: Ambasilide, quinidine, flecainide and verapamil inhibit IKur.d, with preferential action on the open state. IKur.d inhibition may play a role in antiarrhythmic effects in canine atrial arrhythmia models. Comparisons between the effects of these drugs on IKur.d and previously studied effects on IKur suggest potential opportunities for investigating the molecular structural determinants of drug-blocking action on atrial-specific ultrarapid delayed rectifiers. [ABSTRACT FROM PUBLISHER]

Background: We have shown that rapid atrial activation, as occurs during atrial fibrillation (AF), reduces L-type Ca2+ current (ICa) and that this is the principal mechanism of the action potential duration and refractoriness changes that characterize tachycardia-induced atrial remodeling. The present study was designed to determine whether atrial tachycardia alters biochemical indices of the number of L-type Ca2+ channels and/or of the number and binding affinity of β-adrenergic receptors. Methods: In canine atrial sarcolemmal preparations, the number and binding affinity of dihydropyridine receptors were determined with the use of 3H-nitrendipine and that of β-adrenergic receptors with 125I-iodocyanopindolol. Results were obtained with preparations from dogs paced at 400/min for 1 (P1, n=20), 7 (P7, n=9), and 42 (P42, n=9) days, and compared with observations in sham-operated controls (P0, n=14). Results: Pacing reduced the Bmax of dihydropyridine receptors, from 157±18 fmol/mg (P0) to 116±9 fmol/mg (P1, P <0.05), 100±14 fmol/mg (P7, P <0.05) and 94±9 fmol/mg (P42, P <0 .01). The affinity of dihydropyridine receptors was unchanged, with the Kd averaging 711±102 pM, 656±74 pM, 633±155 pM and 585±92 pM in P0, P1, P7 and P42 dogs. Neither Bmax nor Kd of β-adrenergic receptors was altered by rapid pacing. Values of Bmax of dihydropyridine receptors correlated with atrial ICa current density (r2=0.95) and ERP (r2=0.99). Conclusions: Rapid atrial activation results in downregulation in the number of dihydropyridine receptors without altering the number or affinity of β-adrenergic receptors. The reductions in ICa that play an important role in the atrial electrical remodeling by which ‘AF begets AF’ appear to be due at least in part to a decrease in the number of L-type Ca2+ channels in cardiac cell membranes. [ABSTRACT FROM PUBLISHER]

Evaluates the heterogeneity of cardiac action potential (AP), transient potassium efflux current and influx current of potassium in the right ventricle of the human heart. Details on cardiac electrophysiology; Methodology of the study; Results of the study.