Protective effects of protein kinase C during myocardial ischemia require activation of phosphatidyl-inositol specific phospholipase C

Background. Protein kinase C (PKC) activation during myocardial ischemia is thought to be cardioprotective. However, the mechanism of ischemia-induced PKC activation remains unclear. We hypothesized that ischemic PKC activation occurs through activation of phosphatidyl-inositol specific phospholipase C (PI-PLC) and protects the heart from ischemic injury. Methods. Isolated rabbit hearts were subjected to 20 minutes of normothermic ischemia and reperfusion. The PI-PLC inhibitor U73122 (0.5 μmol/L), its inactive analogue U73343 (0.5 μmol/L), or the PKC inhibitor chelerythrine (2 μmol/L) were given just before ischemia. Another group received U73122 plus the direct PKC activator phorbol 12-myristate-13-acetate (PMA, 10 pmol/L). Measurements included contractile function, intracellular calcium, PI-PLC activity, and translocation of PKC isoforms. Results. PI-PLC activity increased during myocardial ischemia and was inhibited by U73122. PI-PLC inhibition prevented the ischemic translocation of PKC-α, PKC-var epsilon, and PKC-η, and impaired cardiac recovery and cytosolic calcium regulation without significant changes in energy metabolism. PMA restored both contractile function and PKC translocation pattern in U73122-treated hearts. Direct PKC inhibition with chelerythrine mimicked the effects of U73122. Conclusions. PI-PLC mediates PKC translocation during myocardial ischemia. Inhibition of PI-PLC or PKC activation, or both, during ischemia significantly impairs postischemic myocardial recovery.