Role of Protein Kinase C- (PKC) in Isoflurane-Induced Cardioprotection

Background: Volatile anaesthetics precondition the heart against infarction, an effect partly mediated by activation of the isoform of protein kinase C (PKC). We investigated whether cardioprotection by activation of PKC depends on the isoflurane concentration.

Methods: Anaesthetized rats underwent 25 min of coronary artery occlusion followed by 120 min of reperfusion and were randomly assigned to the following groups (n=10 in each group): isoflurane preconditioning induced by 15 min administration of 0.4 minimal alveolar concentration (MAC) (0.4MAC), 1 MAC (1MAC) or 1.75 MAC (1.75MAC) followed by 10 min washout before ischaemia. Each protocol was repeated in the presence of the PKC inhibitor staurosporine (10 µg kg^–1): 0.4MAC+S, 1MAC+S and 1.75MAC+S. Controls were untreated (CON) and additional hearts received staurosporine without isoflurane (S). In a second set of experiments (n=6 in each group) hearts were excised before the infarct inducing ischaemia, and phosphorylation and translocation of PKC were determined by western blot analysis.

Results: Isoflurane reduced infarct size from a mean of 61(SEM 2)% of the area at risk in controls to 20(1)% (0.4MAC), 26(3)% (1MAC) and 30(1)% (1.75MAC) (all P<0.01 vs CON or S). This protection was partially reversed by administration of staurosporine in the 0.4MAC+S group (30[2]%; P<0.05 vs 0.4MAC) group, but not after administration of 1 MAC or 1.75 MAC isoflurane (26[2]% and 31[2]%, respectively). Thus 0.4MAC increased PKC phosphorylation, and this effect was blocked by staurosporine. Higher concentrations of isoflurane did not change PKC phosphorylation. PKC was translocated to the membrane fraction after administration of 0.4 MAC isoflurane, but not after 1.0 or 1.75 MAC.

Conclusions: Although isoflurane preconditioning resulted in a reduction in infarct size at all concentrations used, the protection was mediated by phosphorylation and translocation of PKC only at 0.4 MAC.