Background: Cardiac arrhythmias are a leading cause of death in the US. Vast majority of these arrhythmias including catecholaminergic polymorphic ventricular tachycardia (CPVT) are associated with increased levels of circulating catecholamines and involve abnormal impulse formation secondary to aberrant Ca2+ and Na+ handling. However, the mechanistic link between β-AR stimulation and the subcellular/molecular arrhythmogenic trigger(s) remains elusive.
Methods and results: We performed functional and structural studies to assess Ca2+ and Na+ signaling in ventricular myocyte as well as surface electrocardiograms in mouse models of cardiac calsequestrin (CASQ2)-associated CPVT. We demonstrate that a subpopulation of Na+ channels (neuronal Na+ channels; nNav) that colocalize with RyR2 and Na+/Ca2+ exchanger (NCX) 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 the 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.
Conclusion: 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 Nav1.6 in particular can serve as a potential antiarrhythmic therapy.
Keywords: Diastolic Ca2+ release; Neuronal Na+ channels; Ventricular arrhythmias; β-adrenergic receptor.