N-Glycans Modulate hERG1A Window Current

Abstract

Voltage-gated K+ channels are primarily responsible for the repolarization phases of neuronal, skeletal and cardiac muscle action potentials. Activity of the human ether-a-go-go-related gene 1 (hERG1) voltage-gated K+ channel produces a K+ current responsible for much of late phase II and phase III repolarization of the human cardiac action potential. HERG1A has two putative N-glycosylation sites located in the S5-S6 linker region, one of which is N-glycosylated. The aim of this study was to determine whether and how N-linked glycosylation modifies hERG1A channel function. Voltage-dependent gating of hERG1A were evaluated under conditions of full glycosylation, no sialylation, in the absence of complex N-glycans, and following the removal of the full N-glycosylation structure. The hERG1A steady-state activation relationships were shifted along the voltage axis by a significant, depolarizing ∼9 mV under each condition of reduced glycosylation. Steady state channel availability curves were shifted by a much greater depolarizing 20-30 mV under conditions of reduced glycosylation. The depolarizing, non-uniform shifts in voltage-dependent steady state activation and inactivation caused a large rightward shift and an increase in the hERG1A window current. This suggests that reduced glycosylation caused an increase in the persistent hERG current that occurs at more depolarized potentials as observed. This increase and shift in window current would lead to increased hERG1A activity during the action potential, effectively increasing the rate of repolarization, and reducing AP duration, as predicted through in silico modeling of the ventricular AP. Overall, these data indicate a functional role for N-glycosylation in the modulation of hERG1A channel activity, suggesting that even small changes in channel N-glycosylation modulate hERG1A activity, and thereby likely impact the rate of action potential repolarization.