Infarct-sparing effect of myocardial postconditioning dependent on protein kinase C signalling

Objective: Using non-selective and selective protein kinase C (PKC) e and 8 isoform inhibitors, we tested the hypothesis that the cardioprotective phenotype invoked by postconditioning (postcon) is dependent on PKC signalling. Furthermore, we determined whether postconditioning alters pPKC epsilon and/or pPKC delta in cytosolic and mitochondrial fractions. Methods: Male Sprague-Dawley rats underwent 30 min left coronary artery (LCA) occlusion followed by 3 h of reperfusion. Rats were randomised to the following groups: Untreated, no intervention either before or after LCA occlusion; Postcon, 3 cycles of 10-s full reperfusion and 10-s re-occlusion, initiated immediately at the onset of reperfusion; Chelerythrine (non-selective PKC inhibitor, 5 mg/kg) +/- postcon; Rottlerin (PKC delta inhibitor, 0.3 mg/kg) +/- postcon; KIE1-1 (PKC epsilon inhibitor, 3.8 mg/kg) +/- postcon. A subset of rats was employed to assess pPKC epsilon and/or pPKC delta in sham, Isch/RP (30-min LCA occlusion followed by 30-min reperfusion), and postcon-treated hearts. Results: Infarct size, expressed as area of necrosis as a percentage of the area at risk, AN/AAR (%), was significantly reduced by postcon compared to control (untreated) rats (39 +/- 2% vs. 53 +/- 1 % in control, P < 0.001). Treatment with chelerythrine alone or the PKC epsilon antagonist KIE1-1 alone at reperfusion had no effect on infarct size compared to control. In contrast, the infarct-sparing effect of postcon was abrogated by non-selective PKC inhibition and PKC epsilon antagonism (50 +/- 2% and 50 +/- 1%, respectively. P < 0.002). Inhibition of PKC delta reduced infarct size to values comparable to that in postcon group (36 +/- 3% vs. 39 +/- 2%). However, postcon in the presence of PKC delta inhibitor did not enhance the infarct-sparing effects (38 +/- 2%). In addition, pPKC epsilon in postcon hearts was significantly higher in the total cell homogenate (10338 +/- 1627 vs. 4165 +/- 608 in Isch/RP, arbitrary units), and pPKC delta translocation to mitochondria was significantly less (> 2-fold decrease) compared to Isch/RP. Conclusion: These data suggest that postcon modulates PKC during early reperfusion by increasing PKC epsilon expression and translocation to a site other than the outer mitochondrial membrane, and limits translocation of PKC delta to mitochondria and associated deleterious signalling. (c) 2005 European Society of Cardiology. Published by Elsevier B.V All rights reserved.