Differential regulation of voltage-gated K⁺ channels by oxidized and reduced pyridine nucleotide coenzymes

Abstract

The activity of the voltage-sensitive K+ (Kv) channels varies as a function of the intracellular redox state and metabolism, and several Kv channels act as oxygen sensors. However, the mechanisms underlying the metabolic and redox regulation of these channels remain unclear. In this study we investigated the regulation of Kv channels by pyridine nucleotides. Heterologous expression of Kvalpha1.5 in COS-7 cells led to the appearance of noninactivating currents. Inclusion of 0.1-1 mM NAD+ or 0.03-0.5 mM NADP+ in the internal solution of the patch pipette did not affect Kv currents. However, 0.5 and 1 mM NAD+ and 0.1 and 0.5 mM NADP+ prevented inactivation of Kv currents in cells transfected with Kvalpha1.5 and Kvbeta1.3 and shifted the voltage dependence of activation to depolarized potentials. The Kvbeta-dependent inactivation of Kvalpha currents was also decreased by internal pipette perfusion of the cell with 1 mM NAD+. The Kvalpha1.5-Kvbeta1.3 currents were unaffected by the internal application of 0.1 mM NADPH or 0.1 or 1 mM NADH. Excised inside-out patches from cells expressing Kvalpha1.5-Kvbeta1.3 showed transient single-channel activity. The mean open time and the open probability of these currents were increased by the inclusion of 1 mM NAD+ in the perfusate. These results suggest that NAD(P)+ prevents Kvbeta-mediated inactivation of Kv currents and provide a novel mechanism by which pyridine nucleotides could regulate specific K+ currents as a function of the cellular redox state [NAD(P)H-to-NAD(P)+ ratio].