Modulation of KV10.1 Potassium Channel Function by Intracellular Heme

Abstract

Heme, an iron-protoporphyrin-IX complex, is a cofactor bound to various hemoproteins and promotes a broad range of functions, such as electron transfer, oxygen transport, signal transduction, and drug metabolism. In recent years, there has been growing recognition of heme as a non-genomic modulator of ion channel functions. Here, we show that intracellular free heme/hemin modulates human ether à go-go (hEAG1, Kv10.1) voltage-gated potassium channels. We used an integrative approach that combines electrophysiology and biochemical techniques to dissect the impact of heme on human Kv10.1 channels. Electrophysiology experiments were conducted in the inside-out patch-clamp configuration on Xenopus oocytes. Intracellular application of hemin (Fe3+-protoporphyrin-IX) potently inhibited Kv10.1 channels with an apparent IC50 of 4.2±0.3 nM (oxidizing condition) and 63.3±4.5 nM (reducing condition). Hemin did not affect other delayed rectifier K+ channels such as Kv1.1, Kv1.5, and Kv1.6. The onset of the hemin inhibitory effect on the current followed an exponential time course and was very slowly reversible upon washout. Protoporphyrin-IX and Fe2+ were ineffective on Kv10.1 channel currents. Hemin acts as a gating modifier by reducing the probability of channel opening in a voltage-dependent manner. Studies on recombinant channel fragments encompassing the C terminus of Kv10.1 (M478-N673) revealed a heme-responsive binding site in the C-linker region involving histidine 543 and 552. Heme binding to the C-linker possibly induces a conformational constraint that interferes with channel opening. Overall, this study suggested that free heme is a physiologically relevant modulator of Kv10.1 channels activity and neuronal excitability.