THE ROLE OF PROTEIN-KINASE-C IN ISCHEMIC REPERFUSED PRECONDITIONED ISOLATED RAT HEARTS/

Protein kinase C (PKC) has been implicated in the preconditioning-indu ced cardiac protection in ischemic/reperfused myocardium. We studied t he effect of PKC inhibition with calphostin C (25, 50, 100, 200, 400, and 800 nM), a potent and specific inhibitor of PKC, in isolated worki ng nonpreconditioned and preconditioned ischemic/reperfused hearts. In the nonpreconditioned groups, all hearts underwent 30 min of normothe rmic global ischemia followed by 30 min of reperfusion. In the precond itioned groups, hearts were subjected to four cycles of ischemic preco nditioning by using 5 min of ischemia followed by 10 min reperfusion, before the induction of 30 min ischemia and reperfusion. At low concen trations of calphostin C (25, 50, and 100 nM), the PKC inhibitor had n o effect on the incidence of arrhythmias or postischemic cardiac funct ion in the nonpreconditioned ischemic/reperfused groups. With 200 and 400 nM of calphostin C, a significant increase in postischemic functio n and a reduction in the incidence of arrhythmias were observed in the nonpreconditioned ischemic/reperfused groups. Increasing the concentr ation of calphostin C to 800 nM, the recovery of postischemic cardiac function was similar to that of the drug-free control group. In precon ditioned hearts, lower concentrations (<100 nM) of calphostin C did no t change the response of the myocardium to ischemia and reperfusion in comparison to the preconditioned drug-free myocardium. Two hundred an d 400 nM of the PKC inhibitor further reduced the incidence of ventric ular fibrillation (VF) from the preconditioned drug-free value of 50% to 0 (p < 0.05) and 0 (p < 0.05), respectively, indicating that the co mbination of the two, preconditioning and calphostin C, affords signif icant additional protection. Increasing the concentration of calphosti n C to 800 nM blocked the cardioprotective effect of preconditioning ( 100% incidence of VF). The recovery of cardiac function was similarly improved at calphostin C doses of 200 and 400 nM and was reduced at 80 0 nM (p < 0.05). With 200 and 400 nM of calphostin C, both cytosolic a nd particulate PKC activity were reduced by similar to 40 and 60%, res pectively, in both preconditioned and preconditioned/ischemic/reperfus ed hearts. The highest concentration of calphostin C (800 nM) resulted in almost a complete inhibition of cytosolic (100%) and particulate ( 85%) PKC activity correlated with the abolition of preconditioning-ind uced cardiac protection. In conclusion, calphostin C protects the isch emic myocardium obtained from intact animals, provides significant add itional protection to preconditioning at moderate doses, and blocks th e protective effect of preconditioning at high concentrations. The dua l effects of calphostin C appear to be strictly dose and ''enzyme inhi bition'' related.