Downregulation of protein kinase C inhibits activation of mitochondrial K_ATP channels by diazoxide

Background - The mitochondrial K_ATP (mitoK_ATP) channel has been shown to confer short- and long-term cardioprotection against prolonged ischemia via protein kinase C (PKC) signaling pathways. However, the exact association between PKC or its isoforms and mitoK_ATP channels has not yet been clarified. The present study tested the hypothesis that the activity and translocation of PKC to the mitochondria are important for cardiac protection elicited by mitoK_ATP channels. Methods and Results - PKC was downregulated by prolonged (24-hour) treatment with phorbol 12-myristate 13-acetate (4 μg/kg body weight) before subsequent experiments in rats. Langendorff-perfused rat hearts were subjected to 40 minutes of ischemia followed by 30 minutes of reperfusion. Effects of PKC downregulation on the activation of mitoK_ATP channels and other interventions on hemodynamic, biochemical, and pathological changes were assessed. Subcellular localization of PKC isoforms by Western blot analysis and immunocytochemistry demonstrated that PKC-α and PKC-δ were translocated to the sarcolemma and that PKC-δ was translocated to the mitochondria after diazoxide treatment. In hearts treated with diazoxide (80 μmol/L), a significant improvement in cardiac function and an attenuation of cell injury were observed. In PKC-downregulated hearts, protection was abolished because mitoK_ATP channels could not be activated by diazoxide. Conclusions - These data suggest that PKC activation is required for the opening of mitoK_ATP channels during protection against ischemia and that this effect is linked to isoform-specific translocation of PKC-δ to the mitochondria.