Effects of Protein Kinase C Inhibitors inIn Situand Isolated Ischemic Rabbit Myocardium

We tested the effects of the protein kinase C (PKC) inhibitors bisindolylmaleimide (1μ ) and chelerythrine (2μ ) on myocardial ischemia–reperfusion injury inin situand isolated perfused rabbit hearts. In non-ischemic isolated hearts, bisindolylmaleimide (1μ ) and chelerythrine (2μ ) blocked sn-1,2-dioctanoylglycerol (DOG)-induced coronary vasoconstriction by approximately 80%. Intact hearts were subjected to 45 min coronary artery occlusion and 2 h reperfusion. Infarct size, determined by triphenyltetrazolium chloride (TTC)-staining and expressed as percentage of risk area, was reduced approximately 50% by both bisindolylmaleimide (0.05 mg/kg, i.v.) and chelerythrine (0.1 mg/kg, i.v.) compared to vehicle treated controls. In contrast, a higher dose of chelerythrine (3.8 mg/kg, i.v.) did not significantly reduce infarct size. Isolated hearts were subjected to 45 min of global normothermic (37°C) ischemia and 60 min reperfusion. Control hearts exhibited 45±2% recovery of pre-ischemic left ventricular developed pressure (LVDP) compared to bisindolylmaleimide- (73±7%) and chelerythrine-treated hearts (70±11%). Bisindolylmaleimide and cherythrine reduced infarct size from a control value of 24±4 to 8±2 and 9±3%, respectively. Preconditioning isolated hearts with 5 min ischemia and 10 min reperfusion prior to prolonged ischemia reduced infarct size to 10.4±2.3%, an effect which was blocked by chelerythrine (22.5±4.2% infarct size). These results suggest that although PKC may play a role in ischemic preconditioning, PKC inhibitors can be cardioprotective during prolonged ischemia.