Abstract 1095: Oxidoreductase Regulation of Potassium Channels in Rat Ventricle
Oxidative stress contributes to the arrhythmogenic substrate created by myocardial ischemia-reperfusion through changes in cell redox state, a key modulator of protein function. Recent data suggest that redox-sensitive proteins are regulated by intracellular oxidoreductase systems that act as a repair mechanism to reverse oxidative damage. The heart has two major oxidoreductases, thioredoxin (Trx) and glutaredoxin (Grx), but their regulation of ion channels has not been studied. Thus, we examined the roles of the Trx and Grx systems in controlling K+ currents in the ventricle. An oxidative shift in redox state was elicited in isolated rat ventricular myocytes by brief exposure to 100 μM diamide, a thiol-specific, membrane-permeable oxidant. Fluorescence microscopy using a redox-sensitive probe showed that intracellular reduced glutathione was decreased in diamide-treated myocytes by 41% (p<0.05), consistent with cell oxidation. In parallel voltage-clamp studies, diamide decreased peak outward current (Ipeak) evoked by depolarizing test pulses by 42% at +60 mV (p<0.05) while steady-state outward current (Iss) measured at the end of each test pulse was decreased by 46% (+60 mV; p<0.05). These effects were not prevented by calphostin C or GF109203, suggesting diamide did not inhibit K+ currents by activating PKC. Suppression of Ipeak and Iss by diamide was however reversed by activation of glucose utilization with dichloroacetate (DCA) or an insulin-mimetic. The DCA effect on Ipeak was blocked by the Trx system inhibitors auranofin or 13-cis retinoic acid but Iss was not affected by either compound. A non-specific inhibitor of Grx and Trx systems, 1,3-bis-(2-chloroethyl)-1-nitrosourea, also blocked DCA’s effect on Ipeak but only partially inhibited the response of Iss to DCA. These data suggest that cardiac K+ channels are differentially regulated by oxidoreductase systems that are functionally linked to glucose metabolism. Specifically, K+ channels carrying Ipeak (Kv4.x) are controlled by the Trx system whereas channels contributing to Iss (Kv1.5 or Kv2.1) are regulated by the Grx system. We propose that cardiac oxidoreductase systems are important regulators of ion channels under pathogenic conditions associated with oxidative stress.