Oxidoreductase regulation of Kv currents in rat ventricle

Abstract

Oxidative stress contributes to the arrhythmogenic substrate created by myocardial ischemia–reperfusion partly through a shift in cell redox state, a key modulator of protein function. The activity of many oxidation-sensitive proteins is controlled by oxidoreductase systems that regulate the redox state of cysteine thiol groups, but the impact of these systems on ion channel function is not well defined. Thus, we examined the roles of the thioredoxin and glutaredoxin systems in controlling K+ channels in the ventricle. An oxidative shift in redox state was elicited in isolated rat ventricular myocytes by brief exposure to diamide, a thiol-specific, membrane-permeable oxidant. Voltage-clamp studies showed that diamide decreased peak outward K+ current (Ipeak) evoked by depolarizing test pulses by 41% (+60 mV; p<0.05) while steady-state outward current (Iss) measured at the end of the test pulse was decreased by 45% (p<0.05). These electrophysiological effects were not prevented by protein kinase C blockers, but the tyrosine kinase inhibitors genistein or lavendustin A blocked the suppression of both K+ currents by diamide. Moreover, inhibition of Ipeak and Iss by diamide was reversed by dichloroacetate and an insulin-mimetic. The effect of dichloroacetate to normalize Ipeak after diamide was blocked by the thioredoxin system inhibitors auranofin or 13-cis-retinoic acid, but Iss was not affected by either compound. A pan-specific inhibitor of glutaredoxin and thioredoxin systems, 1,3-bis-(2-chloroethyl)-1-nitrosourea, also blocked the dichloroacetate effect on Ipeak but only partially inhibited the recovery of Iss. These data suggest that acute regulation of cardiac K+ channels by oxidoreductase systems is mediated by redox-sensitive tyrosine kinase/phosphatase pathways. The pathways controlling Ipeak channels are targets of the thioredoxin system whereas those regulating Iss channels are likely controlled by the glutaredoxin system. Thus, cardiac oxidoreductase systems may be important regulators of ion channels affected by pathogenic oxidative stress.