Generation of metabolic oscillations by mitoKATP and ATP synthase during simulated ischemia in ventricular myocytes

Metabolic oscillations and the concomitant periodic activations of sarcolemmal ATP-sensitive K+ channels (sarcKATP) have recently been proposed as one mechanism underlying ischemia-related arrhythmia. In this study, we investigated the role of mitochondrial ATP-sensitive K+ channels (mitoKATP) and ATP synthase in the generation of metabolic oscillations during simulated ischemia from rat ventricular myocytes using patch-clamp technique and fluorescence microscopy. We have found that the combined application of creatine kinase (CK) inhibitor, 2,4-dinitrofluorobenzene, with cyanide, electron-transport-chain inhibitor causes oscillatory activations of sarcKATP. The oscillatory activations of sarcKATP were accompanied by large periodic depolarizations in mitochondrial membrane potential (Ψm). 5-Hydroxydecanoate, an inhibitor of mitoKATP, halted the oscillations in Ψm at repolarized state, whereas oligomycin, an inhibitor of ATP synthase, halted them at depolarized state. In both conditions, oscillatory activations of sarcKATP were abolished. Inhibitors of adenine nucleotide translocator and permeability transition pore had no effect on the oscillations in Ψm and sarcKATP. 4,4′-diisothiocyanatostilbene-2,2′-disulfonate, an inhibitor of mitochondrial inner-membrane anion channel (IMAC), caused a full depolarization in Ψm and activation of sarcKATP, finally resulting in irreversible hypercontracture. Taken together, oscillations in Ψm can be explained by balance between depolarizing power of mitoKATP and repolarizing power of the reverse activity of ATP synthase. ATP consumption by ATP synthase in reverse mode links periodic depolarizations in Ψm to oscillatory activation of sarcKATP. Considering that such oscillations were not induced by cyanide alone, CK system may act as an important buffer, inhibiting arrhythmia during ischemia.