Selective pharmacological agents implicate mitochondrial but not sarcolemmal K(ATP) channels in ischemic cardioprotection

Background - Pharmacological evidence has implicated ATP-sensitive K⁺ (K(ATP)) channels as the effectors of cardioprotection, but the relative roles of mitochondrial (mitoK(ATP)) and sarcolemmal (surfaceK(ATP)) channels remain controversial. Methods and Results - We examined the effects of the K(ATP) channel blocker HMR1098 and the K(ATP) channel opener P-1075 on surfaceK(ATP) and mitoK(ATP) channels in rabbit ventricular myocytes. HMR1098 (30 μmol/L) inhibited the surfaceK(ATP) current activated by metabolic inhibition, whereas the drug did not blunt diazoxide (100 μmol/L)-induced flavoprotein oxidation, an index of mitoK(ATP) channel activity. P-1075 (30 μmol/L) did not increase flavoprotein oxidation but did elicit a robust surfaceK(ATP) current that was completely inhibited by HMR1098. These results indicate that HMR1098 selectively inhibits surfaceK(ATP) channels, whereas P- 1075 selectively activates surface K(ATP) channels. In a cellular model of simulated ischemia, the mitoK(ATP) channel opener diazoxide (100 μmol/L), but not P-1075, blunted cellular injury. The cardioprotection afforded by diazoxide or by preconditioning was prevented by the mitoK(ATP) channel blocker 5-hydroxydecanoate (500 μmol/L) but not by the surfaceK(ATP) channel blocker HMR1098 (30 μmol/L). Conclusions - The cellular effects of mitochondria- or surface-selective agents provide further support for the emerging consensus that mitoK(ATP) channels rather than surfaceK(ATP) channels are the likely effectors of cardioprotection.