Excessive ATP hydrolysis in ischemic myocardium by mitochondrial F 1F0-ATPase: effect of selective pharmacological inhibition of mitochondrial ATPase hydrolase activity. synthesizes ATP in the heart, but under ischemic conditions this enzyme paradoxically causes ATP hydrolysis. Nonselective inhibitors of this enzyme (aurovertin, oligomycin) inhibit ATP synthesis in normal tissue but also inhibit ATP hydrolysis in ischemic myocardium. We characterized the profile of aurovertin and oligomycin in

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... schemic and nonischemic rat myocardium and compared this with the profile of BMS-199264, which only inhibits F 1F0-ATP hydrolase activity. In isolated rat hearts, aurovertin (1-10 M) and oligomycin (10 M), at concentrations inhibiting ATPase activity, reduced ATP concentration and contractile function in the nonischemic heart but significantly reduced the rate of ATP depletion during ischemia. They also inhibited recovery of reperfusion ATP and contractile function, consistent with nonselective F 1F0-ATPase inhibitory activity, which suggests that upon reperfusion, the hydrolase activity switches back to ATP synthesis. BMS-199264 inhibits F 1F0 hydrolase activity in submitochondrial particles with no effect on ATP synthase activity. BMS-199264 (1-10 M) conserved ATP in rat hearts during ischemia while having no effect on preischemic contractile function or ATP concentration. Reperfusion ATP levels were replenished faster and necrosis was reduced by BMS-199264. ATP hydrolase activity ex vivo was selectively inhibited by BMS-199264. Therefore, excessive ATP hydrolysis by F 1F0-ATPase contributes to the decline in cardiac energy reserve during ischemia and selective inhibition of ATP hydrolase activity can protect ischemic myocardium. ischemia; heart; reperfusion MITOCHONDRIAL F 1 F 0 -ATPASE is responsible for the majority of ATP production in the heart. Synthesis of ATP in the mitochondria requires a proton gradient across the inner membrane, which is generated by the respiratory proteins as electrons are transferred to oxygen. ATP synthesis by the catalytic F 1 domain is driven by transport of protons into the matrix through the F 0 domain (10, 28). Oxygen deprivation collapses the mitochondrial electrochemical gradient, which switches F 1 F 0 -ATPase from ATP synthesis to ATP hydrolysis (11, 25, 32) . In ischemic myocardium, this may cause excessive and wasteful hydrolysis of ATP, which does not contribute to cardiac work.