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Circulation Research July 20, 2012 Journal Club Functional NaV1.8 Channels in Intracardiac Neurons / Novelty and Significance: The Link Between SCN10A and Cardiac Electrophysiology Arie O. Verkerk, Carol Ann Remme, Cees A. Schumacher, Brendon P. Scicluna, Rianne Wolswinkel, Berend de Jonge, Connie R. Bezzina, and Marieke W. Veldkamp Circ Res. 2012;111:333-343. PDF: http://circres.ahajournals.org/content/111/3/333.full.pdf+html Related Article, Yang et al [PDF]: Blocking Scn10a Channels in Heart Reduces Late Sodium Current and Is Antiarrhythmic Related Editorial by Barry London [PDF]: Whither Art Thou, SCN10A, and What Art Thou Doing? Included in the Journal Club pack: Abstract, Novelty & Significance section, and all figures. Functional NaV1.8 Channels in Intracardiac Neurons / Novelty and Significance: The Link Between SCN10A and Cardiac Electrophysiology Abstract Rationale: The SCN10A gene encodes the neuronal sodium channel isoform NaV1.8. Several recent genome-wide association studies have linked SCN10A to PR interval and QRS duration, strongly suggesting an as-yet unknown role for NaV1.8 in cardiac electrophysiology. Objective: To demonstrate the functional presence of SCN10A/Nav1.8 in intracardiac neurons of the mouse heart. Methods and Results: Immunohistochemistry on mouse tissue sections showed intense NaV1.8 labeling in dorsal root ganglia and intracardiac ganglia and only modest NaV1.8 expression within the myocardium. Immunocytochemistry further revealed substantial NaV1.8 staining in isolated neurons from murine intracardiac ganglia but no NaV1.8 expression in isolated ventricular myocytes. Patch-clamp studies demonstrated that the NaV1.8 blocker A-803467 (0.5–2 μmol/L) had no effect on either mean sodium current (INa) density or INa gating kinetics in isolated myocytes but significantly reduced INa density in intracardiac neurons. Furthermore, A-803467 accelerated the slow component of current decay and shifted voltage dependence of inactivation toward more negative voltages, as expected for blockade of NaV1.8based INa. In line with these findings, A-803467 did not affect cardiomyocyte action potential upstroke velocity but markedly reduced action potential firing frequency in intracardiac neurons, confirming a functional role for NaV1.8 in cardiac neural activity. Conclusions: Our findings demonstrate the functional presence of SCN10A/NaV1.8 in intracardiac neurons, indicating a novel role for this neuronal sodium channel in regulation of cardiac electric activity. Novelty and Significance What Is Known? The sodium channel isoform NaV1.8 (encoded by the SCN10A gene) is highly expressed in neurons of the dorsal root ganglia and cranial sensory ganglia, where it is involved in generating and maintaining action potentials and controlling neuronal firing patterns. Several recent genome-wide association studies have linked SCN10A to PR interval and QRS duration on the ECG, but the precise localization and role of NaV1.8/SCN10A in the heart remains unknown. What New Information Does This Article Contribute? NaV1.8-based sodium channels are absent in cardiomyocytes but are present in the intracardiac neurons of the murine heart. NaV1.8 blockade markedly reduces action potential firing frequency in intracardiac neurons. NaV1.8/SCN10A might affect myocardial electrophysiological properties through regulation of cardiac neural activity. The SCN10A gene encodes the sodium channel isoform NaV1.8, which is known to be highly expressed in neuronal tissue, particularly in the dorsal root ganglia. In recent studies, a strong genetic link between SCN10A and cardiac conduction has been demonstrated, but the precise localization and functional role of SCN10A/Nav1.8 in the heart is debated. We investigated the expression of Nav1.8 in various regions and cell types of the murine heart. NaV1.8 was absent from cardiomyocytes, but its expression was observed in neurons of intracardiac ganglia originating from the pulmonary vein region. Accordingly, pharmacological blockade of NaV1.8 had no electrophysiological effect in isolated cardiomyocytes but reduced sodium current density and action potential firing frequency in isolated intracardiac neurons. Our findings thus demonstrate a novel role for SCN10A/Nav1.8 in determining myocardial electrophysiological properties through regulation of cardiac neural activity. Furthermore, we have identified cardiac neuronal sodium channels as potential novel targets for future studies in arrhythmia research.. Expression and localization of NaV1.8 in embryonic (A through C) and adult (D through F) mouse tissue (scale bars A and C: 100 μm; B, D, E, and F: 50 μm). Verkerk A O et al. Circulation Research 2012;111:333-343 Copyright © American Heart Association NaV1.8 expression in isolated cells (scale bars A and B, 25 μm; C, 50 μm). Verkerk A O et al. Circulation Research 2012;111:333-343 Copyright © American Heart Association Effects of the NaV1.8 selective blocker A-803467 on sodium current density and gating in isolated mouse intracardiac neurons. Verkerk A O et al. Circulation Research 2012;111:333-343 Copyright © American Heart Association Effects of the NaV1.8 selective blocker A-803467 on sodium current density and gating in isolated mouse ventricular myocytes. Verkerk A O et al. Circulation Research 2012;111:333-343 Copyright © American Heart Association Effects of the NaV1.8 selective blocker A-803467 on action potentials from single mouse atrial and ventricular myocytes. Verkerk A O et al. Circulation Research 2012;111:333-343 Copyright © American Heart Association Action potential firing characteristics of intracardiac neurons under basal conditions. Verkerk A O et al. Circulation Research 2012;111:333-343 Copyright © American Heart Association NaV1.8 channels regulate action potential firing pattern in isolated intracardiac neurons. Verkerk A O et al. Circulation Research 2012;111:333-343 Copyright © American Heart Association