A de novo arrhythmogenic Nav1.5 variant, E171Q, causes multiple biophysical defects.

Abstract

An infant presenting antenatally with cardiac conduction disease and junctional tachycardia reminiscent of the multi-focal ectopic Purkinje-related premature contractions (MEPPC) syndrome was found to harbour the de novo E171Q variant of the cardiac voltage-gated sodium channel, Nav1.5. Functional analysis was performed using whole cell patch clamp and current clamp to compare WT Nav1.5 with E171Q expressed in HEK293 cells and iPSC-CMs. We found E171Q significantly right-shifted the voltage-dependence of both activation and steady-state fast inactivation, and increased the amplitude of late sodium current. These changes were reversed upon perfusion with 100 μM ranolazine. Incorporating the shifts in voltage-dependence and late current into the Ohara-Rudy cardiac action potential model produced a delay in action potential repolarization. Further investigation revealed a significant outward gating pore (omega) current in E171Q that was mitigated upon perfusion of 3 μM flecainide or with K+-free internal solution. Current clamp experiments in iPSC-CMs revealed action potential variability with delayed afterdepolarizations in myocytes expressing E171Q. The increase in gating pore current is consistent with disrupting the interaction between E171 and a corresponding positive charge in the S4 voltage sensor. This disruption could result in the completion of an ion-permeable pore, consistent with that previously described for Nav1.5 R222Q - a variant also associated with MEPPC - and Nav1.4 R222W.