Opening of Mitochondrial K ATP Channels Attenuates the Ouabain-Induced Calcium Overload in Mitochondria

Abstract

We tested whether opening of mitochondrial ATP-sensitive K + (mitoK ATP ) channels depolarizes mitochondrial membrane potential (ΔΨ m ) and thereby prevents the mitochondrial Ca 2+ overload. With the use of a Nipkow disk confocal system, the mitochondrial Ca 2+ concentration ([Ca 2+ ] m ) and ΔΨ m in rat ventricular myocytes were measured by loading cells with Rhod-2 and JC-1, respectively. Exposure to ouabain (1 mmol/L) for 30 minutes produced mitochondrial Ca 2+ overload, and the intensity of Rhod-2 fluorescence significantly increased to 173±16% of baseline ( P <0.001). Treatment of myocytes with the mitoK ATP channel opener diazoxide (100 μmol/L) blunted the ouabain-induced mitochondrial Ca 2+ overload (131±10% of baseline; P <0.001 versus ouabain). Moreover, diazoxide significantly depolarized the ΔΨ m and reduced the intensity of JC-1 fluorescence during application of ouabain to 89±2% of baseline ( P <0.05). These effects of diazoxide were blocked by the mitoK ATP channel blocker 5-hydroxydecanoate (500 μmol/L). These results indicate that opening of mitoK ATP channels prevents a mitochondrial Ca 2+ overload in association with ΔΨ m depolarization and thereby protects myocardium against ischemic damage.