Mitochondrial ATP-Sensitive Potassium Channels Inhibit Apoptosis Induced by Oxidative Stress in Cardiac Cells

Abstract

Abstract —Mitochondria can either enhance or suppress cell death. Cytochrome c release from mitochondria and depolarization of the mitochondrial membrane potential (ΔΨ) 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 μmol/L hydrogen peroxide induced TUNEL positivity, cytochrome c translocation, caspase-3 activation, poly(ADP-ribose) polymerase cleavage, and dissipation of ΔΨ. Pharmacological opening of mitoK ATP channels by diazoxide (100 μmol/L) preserved mitochondrial integrity and suppressed all markers of apoptosis. Diazoxide prevented ΔΨ depolarization in a concentration-dependent manner (EC 50 ≈40 μmol/L, with saturation by 100 μmol/L), as shown by both flow cytometry and quantitative image analysis of cells stained with fluorescent ΔΨ 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 μmol/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.