DOES PROTEIN-KINASE-C PLAY A ROLE IN ISCHEMIC PRECONDITIONING IN RAT HEARTS

Protein kinase C (PKC) has been implicated in the cardioprotective effects of ischemic preconditioning in rabbits, but whether it plays a role in rats is unknown. We tested this preconditioning PKC theory by assessing whether the inhibition of PKC with calphostin C, a potent and specific inhibitor of PKC, can block the preconditioning effects in this model. Four groups of rats were studied: 1) control + vehicle, 2) control + calphostin C, 3) preconditioning + vehicle, and 4) preconditioning + calphostin C. All rats underwent 90 min of coronary occlusion followed by 4 h of reperfusion; in addition, preconditioned rats underwent three 3-min episodes of ischemia and 5 min of reperfusion before the 90 min of ischemia. Two injections of vehicle or calphostin C (0.1 mg/kg) were administered in intravenous boluses 29 min and 3 min before the 90-min coronary occlusion, i.e., one dose was given 5 min before preconditioning, and another dose was given between preconditioning and the sustained 90 min of ischemia in preconditioned rats. After 4 h of reperfusion, the area at risk (AR) was delineated by dye injection and area of necrosis was assessed by triphenyltetrazolium chloride staining. The electrocardiogram was recorded for the incidence of ventricular tachycardia (VT) and ventricular fibrillation. AR was similar in all four groups. In the nonpreconditioned control rats receiving vehicle, myocardial infarct size expressed as a percentage of the AR averaged 45.7 +/- 1.7%. Pretreatment with calphostin C had no effect on infarct size (48.9 +/- 3.4%) in nonpreconditioned control rats. Preconditioned rats that received vehicle demonstrated a significant reduction in infarct size (11.9 +/- 2.6%, P < 0.01 vs. controls). However, calphostin C completely blocks the effect of preconditioning on infarct size (47.3 +/- 5.8%, P < 0.01 vs, preconditioning + vehicle and P = not significant vs. controls). Similar to the infarct size, calphostin C alone did not alter the incidence of VT during the 90 min of ischemia in nonpreconditioned control rats (100%), and the incidence was significantly attenuated in the preconditioning + vehicle group (30%, P < 0.05 vs. control + vehicle). But calphostin C did block preconditioning's effect on VT (80% in preconditioning + calphostin C group). These data suggest that PKC may be important for ischemic preconditioning's beneficial effect on infarct size in the rat model.