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.