Abstract 1512: Redox Modulation of Voltage-Dependent K+ (KV) Channels Mediates H2O2-Induced Coronary Vasodilation
H2O2 is a proposed metabolic vasodilator, endothelium-derived hyperpolarizing factor, and mediator of flow-induced dilation in the coronary circulation. We have demonstrated that 4-aminopyrdine (4-AP), an inhibitor of KV channels, significantly attenuates H2O2-induced coronary vasodilation. Importantly, however, data are lacking that demonstrate H2O2 activates KV channels in coronary vascular smooth muscle. Thus, we used patch clamp electrophysiology to test the hypothesis that H2O2 increases KV current in smooth cells freshly isolated from canine left circumflex artery. Further, we used K+ channel antagonists and sulfhydryl-reactive reagents to determine the pharmacological nature and redox-sensitivity of H2O2-activated K channels. H2O2 increased whole-cell K+ channel current in a concentration-dependent manner; the most prominent effect of H2O2 was noted between -30 and 0 mV. H2O2 also increased the amplitude of tail currents characteristic of KV channels, but did not alter the voltage-dependence of channel activation or inactivation. Tetraethylammonium (1 mM; TEA) and iberiotoxin (100 nM) significantly reduced whole-cell K+ current at positive potentials; however, neither of those K+ channel antagonists limited ability of H2O2 to increase K+ current in the physiological range of membrane potentials. 4-AP (3 mM) significantly inhibited whole-cell K+ current at potentials positive to -30 mV and prevented the effect of H2O2 to increase K+ current. Together, these data suggest that 4-AP-sensitive KV channels, not TEA- or iberiotoxin-sensitive Ca2+-activated K+ channels, are activated by H2O2. Dithiothreitol (1 mM), a thiol reductant, significantly reduced KV current and also reversed the effect of H2O2 on KV current. N-ethylmaliemide (5 mM), a thiol alkylating agent, prevented the effect of H2O2 to increase KV current. Our data indicate that H2O2 increases the activity of 4-AP-sensitive KV channels coronary vascular smooth muscle cells. H2O2 influences the activity of these 4-AP-senstive KV channels by changing the oxidation state of thiol groups. We conclude that KV channels in the coronary circulation are redox-sensitive and likely mediate coronary vasodilation in response to H2O2.