Mitochondrial ATP-sensitive potassium channels inhibit apoptosis induced by oxidative stress in cardiac cells

Mitochondria can either enhance or suppress cell death, Cytochrome c release from mitochondria and depolarization of the mitochondrial membrane potential (Delta Psi) are crucial events in triggering apoptosis, In contrast, activation of mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels prevents lethal ischemic injury in vivo, implicating these channels as key players in the process of ischemic preconditioning. We probed the relationship between mitoK(ATP) channels and apoptosis in cultured neonatal rat cardiac ventricular myocytes. Incubation with 200 mu mol/L, hydrogen peroxide induced TUNEL positivity, cytochrome c translocation, caspase-3 activation, poly(ADP ribose) polymerase cleavage, and dissipation of Delta Psi. Pharmacological opening of mitoK(ATP) channels by diazoxide (100 mu mol/L) preserved mitochondrial integrity and suppressed all markers of apoptosis. Diazoxide prevented Delta Psi depolarization in a concentration-dependent manner (EC50 approximate to 40 mu mol/L, with saturation by 100 mu mol/L), as shown by both flow cytometry and quantitative image analysis of cells stained with fluorescent Delta Psi indicators. These cytoprotective effects of diazoxide were reproduced by pinacidil, another mitoK(ATP) agonist, and blocked by the mitoK(ATP) channel antagonist 5-hydroxydecanoate (500 mu mol/L). Our findings identify a novel mitochondrial pathway that is protective against apoptosis. The results also pinpoint mitoK(ATP) channels as logical therapeutic targets in diseases of enhanced apoptosis and oxidative stress.