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

Abstract

We tested whether opening of mitochondrial ATP-sensitive K+ (mitoKATP) channels depolarizes mitochondrial membrane potential (ΔΨm) and thereby prevents the mitochondrial Ca2+ overload. With the use of a Nipkow disk confocal system, the mitochondrial Ca2+ concentration ([Ca2+]m) and ΔΨm 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 mitoKATP channel opener diazoxide (100 μmol/L) blunted the ouabain-induced mitochondrial Ca2+ overload (131±10% of baseline; P<0.001 versus ouabain). Moreover, diazoxide significantly depolarized the ΔΨm 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 mitoKATP channel blocker 5-hydroxydecanoate (500 μmol/L). These results indicate that opening of mitoKATP channels prevents a mitochondrial Ca2+ overload in association with Δψm depolarization and thereby protects myocardium against ischemic damage.