Neuronal Na+ Channels Are Integral Components of Pro-Arrhythmic Na+/Ca2+ Signaling Nanodomain That Promotes Cardiac Arrhythmias During β-Adrenergic Stimulation

• CPVT is often caused by increased levels of circulating catecholamines; however, the mechanistic link between β-AR stimulation and the subcellular/molecular arrhythmogenic trigger(s) is unclear.
• In both CPVT and wild type mice, a subpopulation of Na+ channels (nNav) colocalize with RyR2 and NCX.
• Augmented Na+ entry via nNav and enhanced SR Ca2+-ATPase (SERCA)-mediated SR Ca2+ refill are both essential and necessary for CPVT.
• Augmentation of Na+ entry involves β-AR–mediated activation of Ca2+/CAMKII.
• Selective pharmacological blockade as well as silencing of Nav1.6 inhibit myocyte arrhythmic potential and prevent arrhythmias in vivo.

SummaryAlthough triggered arrhythmias including catecholaminergic polymorphic ventricular tachycardia (CPVT) are often caused by increased levels of circulating catecholamines, the mechanistic link between β-adrenergic receptor (AR) stimulation and the subcellular/molecular arrhythmogenic trigger(s) is unclear. Here, we systematically investigated the subcellular and molecular consequences of β-AR stimulation in the promotion of catecholamine-induced cardiac arrhythmias. Using mouse models of cardiac calsequestrin-associated CPVT, we demonstrate that a subpopulation of Na+ channels, mainly the neuronal Na+ channels (nNav), colocalize with ryanodine receptor 2 (RyR2) and Na+/Ca2+ exchanger (NCX) and are a part of the β-AR-mediated arrhythmogenic process. Specifically, augmented Na+ entry via nNav in the settings of genetic defects within the RyR2 complex and enhanced sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA)-mediated SR Ca2+ refill is both an essential and a necessary factor for arrhythmogenesis. Furthermore, we show that augmentation of Na+ entry involves β-AR–mediated activation of CAMKII, subsequently leading to nNav augmentation. Importantly, selective pharmacological inhibition as well as silencing of Nav1.6 inhibit myocyte arrhythmic potential and prevent arrhythmias in vivo. Taken together, these data suggest that the arrhythmogenic alteration in Na+/Ca2+ handling evidenced ruing β-AR stimulation results, at least in part, from enhanced Na+ influx through nNav. Therefore, selective inhibition of these channels and of Nav1.6 in particular can serve as a potential antiarrhythmic therapy.

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