Activation of Mitochondrial ATP-Sensitive K + Channel for Cardiac Protection Against Ischemic Injury Is Dependent on Protein Kinase C Activity

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Abstract
—Protein kinase C (PKC) is involved in the second messenger signaling cascade during ischemic and Ca 2+ preconditioning. Given that the pharmacological activation of mitochondrial ATP-sensitive K + (mitoK ATP ) channels also mimics preconditioning, the mechanisms linking PKC activation and mitoK ATP channels remain to be established. We hypothesize that PKC activity is important for the opening of the mitoK ATP channel. To examine this, a specific opener of the mitoK ATP channel, diazoxide, was used in conjunction with subcellular distribution of PKC in a model of ischemia/reperfusion (I/R). Langendorff-perfused rat hearts were subjected to 40-minute ischemia followed by 30-minute reperfusion. Effects of activation of the mitoK ATP channel and other interventions on functional, biochemical, and pathological changes in ischemic hearts were assessed. In hearts treated with diazoxide, left ventricular end-diastolic pressure and coronary flow were significantly improved after I/R; lactate dehydrogenase release was also significantly decreased. The morphology was well preserved in diazoxide-treated hearts compared with nontreated ischemic control hearts. The salutary effects of diazoxide on the ischemic injury were similar to those of Ca 2+ preconditioning. Administration of sodium 5-hydroxydecanoate, an effective blocker of the mitoK ATP channel, or chelerythrine or calphostin C, an inhibitor of PKC, during diazoxide pretreatment or during continuous presence of diazoxide in the ischemic period, completely abolished the beneficial effects of the diazoxide on the I/R injury. Blockade of Ca 2+ entry during diazoxide treatment by inhibiting the L-type Ca 2+ channel with verapamil also completely reversed the beneficial effect of diazoxide during I/R. PKC-α was translocated to sarcolemma, whereas PKC-δ was translocated to the mitochondria and intercalated disc, and PKC-ε was translocated to the intercalated disc of the diazoxide-pretreated hearts. Colocalization studies for mitochondrial distribution with tetramethylrhodamine ethyl ester (TMRE) and PKC isoforms by immunoconfocal microscopy revealed that PKC-δ antibody specifically stained the mitochondria. ATP was significantly increased in the diazoxide-treated hearts. Moreover, the data suggest that activation and translocation of PKC to mitochondria appear to be important for the protection mediated by mitoK ATP channel.

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