Diacylglycerol delays pH(i) overshoot after reperfusion and attenuates contracture in isolated, paced myocytes

Although protein kinase C (PKC) plays a pivotal role in ischemic preconditi oning, it is not clear what the end effector is that protects the myocardiu m. In isolated, paced (1.25 Hz, 36-37 degrees C) adult rat cardiomyocytes, the effects of PKC preactivation by diacylglycerol on cell motion, intracel lular Ca2+ concentration ([Ca2+](i); indo 1), and intracellular pH (pH(i); seminaphthorhodafluor-1) during simulated ischemia-reperfusion (I/R) were i nvestigated. The degree of reperfusion-induced contracture was significantl y attenuated in the myocytes pretreated with 10 mu M 1,2-dioctanoyl-sn-glyc erol (DOG; n = 19) compared with the untreated myocytes (n = 23, P < 0.02). There were no differences in twitch amplitude, end-diastolic [Ca2+]i, or p eak-systolic [Ca2+](i) during I/R between the DOG-pretreated and untreated myocytes. Although there were no differences in pH(i) during ischemia, the pH(i) overshoot during reperfusion was significantly delayed in the DOG-pre treated myocytes compared with the untreated myocytes (n = 17 for each, P < 0.01). Chelerythrine completely abolished the favorable effects of DOG on the reperfusion-induced contracture and the pH(i) overshoot. These data sug gest that diacylglycerol attenuates I/R injury in isolated, paced cardiomyo cytes, which may be related to the slower pH(i) overshoot during reperfusio n.