PO-615-04 SODIUM CHANNEL REMODELING UNDERLIES CARDIAC ARRHYTHMIAS IN A MURINE MODEL OF SUDDEN DEATH IN EPILEPSY

Abstract

Dravet Syndrome (DS) is an inherited epileptic condition mostly associated with loss of SCN1A (NaV1.1) function. DS patients have a higher risk of sudden unexpected death in epilepsy (SUDEP) linked to arrhythmia. But mechanisms of arrhythmia in DS remain unknown. Intriguingly, DS cardiac myocytes exhibit a paradoxical increase in late Na+ currents (INa). Furthermore, reducing Nav1.6 decreases the incidence of seizures, suggesting a possible link between Nav1.6 and arrhythmia in DS. Here we hypothesize that NaV1.6 remodeling, particularly near ryanodine receptor 2 (RyR2) and Na+/Ca2+ exchange (NCX), underlies Ca2+ mishandling and arrhythmias in DS. To investigate dysregulation of cardiac NaVs and its arrhythmogenic impact in DS. Western blot, proximity ligation assay (PLA), stochastic optical reconstruction microscopy (STORM), patch clamp, Ca2+ imaging, in vivo ECG. A mouse model of DS (NaV1.1+/-) exhibited similar NaV1.5 expression levels relative to wild type (WT); however, expression of NaV1.6 was increased in DS hearts. To investigate the structural context of increased NaV1.6 expression we used PLA (<40 nm) and STORM (< 20 nm lateral resolution) to assess the density of NaV1.6 near RyR2 and NCX. PLA demonstrated higher frequency of co-localization between NaV1.6 and RyR2 and NCX in DS relative to WT. This correlated with increase in fraction of NaV1.6 clusters near (<100 nm) RyR2 in DS comparing to WT as revealed by STORM. To asses functional consequences of NaV1.6 cluster remodeling, we used whole-cell INa patch clamp recording and confocal Ca2+ imaging. These studies revealed that DS cardiomyocytes evidenced enhanced late INa coupled with increased frequency of Ca2+ waves. Global suppression of NaV1.6 (DS × NaV1.6+/-) mitigated late INa as well as aberrant Ca2+ handling. Using in vivo ECG we found that during bradycardia challenge (carbachol 0.5 mg/kg intraperitoneal) DS mice exhibited higher incidence of VT relative to WT and DS × NaV1.6+/-. Importantly, VT incidence correlated with increased mortality of DS mice. Remodeling within NaV1.6-rich nanodomains contributes to Ca2+ mishandling and arrhythmia in DS that may underlie SUDEP. NaV1.6 may serve as a druggable target for arrhythmia and SUDEP prevention.