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 microgram/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-alpha and PKC-delta were translocated to the sarcolemma and that PKC-delta was translocated to the mitochondria after
diazoxide treatment. In hearts treated with
diazoxide (80 micromol/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-delta to the mitochondria.