Opening of mitochondrial KATP channels attenuates the ouabain-induced calcium overload in mitochondria

We tested whether opening of mitochondrial ATP-sensitive K+ (mitoK(ATP)) channels depolarizes mitochondrial membrane potential (Delta Psi (m)) and thereby prevents the mitochondrial Ca2+ overload. With the use of a Nipkow disk confocal system, the mitochondrial Ca2+ concentration ([Ca2+](m)) and Delta Psi (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 Ca2+ 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 mu mol/L) blunted the ouabain-induced mitochondrial Ca2+ overload (131 +/- 10% of baseline; P <0.001 versus ouabain). Moreover, diazoxide significantly depolarized the Delta Psi (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 mu mol/L). These results indicate that opening of mitoK(ATP) channels prevents a mitochondrial Ca2+ overload in association with Delta Psi (m). depolarization and thereby protects myocardium against ischernic damage.