K(V)4.3 Expression Modulates Na(V)1.5 Sodium Current

In cardiomyocytes, the voltage-gated transient outward potassium current (I(to)) is responsible for the phase-1 repolarization of the action potential (AP). Gain-of-function mutations in KCND3, the gene encoding the I(to) carrying K(V)4.3 channel, have been associated with Brugada syndrome (BrS). While the role of I(to) in the pro-arrhythmic mechanism of BrS has been debated, recent studies have suggested that an increased I(to) may directly affect cardiac conduction. However, the effects of an increased I(to) on AP upstroke velocity or sodium current at the cellular level remain unknown. We here investigated the consequences of K(V)4.3 overexpression on Na(V)1.5 current and consequent sodium channel availability. We found that overexpression of K(V)4.3 protein in HEK293 cells stably expressing Na(V)1.5 (HEK293-Na(V)1.5 cells) significantly reduced Na(V)1.5 current density without affecting its kinetic properties. In addition, K(V)4.3 overexpression decreased AP upstroke velocity in HEK293-Na(V)1.5 cells, as measured with the alternating voltage/current clamp technique. These effects of K(V)4.3 could not be explained by alterations in total Na(V)1.5 protein expression. Using computer simulations employing a multicellular in silico model, we furthermore demonstrate that the experimentally observed increase in K(V)4.3 current and concurrent decrease in Na(V)1.5 current may result in a loss of conduction, underlining the potential functional relevance of our findings. This study gives the first proof of concept that K(V)4.3 directly impacts on Na(V)1.5 current. Future studies employing appropriate disease models should explore the potential electrophysiological implications in (patho)physiological conditions, including BrS associated with KCND3 gain-of-function mutations.