Warm-blood cardioplegic arrest induces selective mitochondrial translocation of protein kinase Cε followed by interaction with 6.1 inwardly rectifying potassium channel subunit in viable myocytes overexpressing urocortin

ObjectiveThis study investigates the cardioprotective role and mechanism of action of urocortin in patients undergoing cardiac surgery, with respect to protein kinase Cε expression, activation, and relocation.BackgroundCardioplegic arrest and subsequent reperfusion inevitably expose the heart to iatrogenic ischemia/reperfusion injury. We previously reported that iatrogenic ischemia/reperfusion injury caused myocyte induction of urocortin, an endogenous cardioprotective peptide.MethodsTwo sequential biopsies were obtained from the right atrium of 25 patients undergoing coronary artery bypass grafting at the start of grafting (internal control) and 10 minutes after release of the aortic clamp.ResultsIn hearts exposed to iatrogenic ischemia/reperfusion injury, induction of urocortin was documented at both the mRNA (255% of basic levels; P < .05) and the protein (4-fold increase; P < .01) levels. Iatrogenic ischemia/reperfusion injury also induced a selective increase of protein kinase Cε mRNA (225% of internal control; P < .05) and a 2-fold overexpression of total protein kinase Cε (P < .05), which paralleled a 2.9-fold increase in protein kinase Cε phosphorylation (P < .01). Mitochondrial translocation of activated protein kinase Cε was observed only in postcardioplegic samples, using both subcellular fractionation (P < .05) and immunostaining techniques (P < .05). Enhanced protein kinase Cε/mitochondria colocalization was selectively observed in viable myocytes, showing concurrently positive staining for urocortin (P < .05). Finally, co immunoprecipitation experiments documented an iatrogenic ischemia/reperfusion injury-enhanced physical interaction of phosphorylated protein kinase Cε with the 6.1 inwardly rectifying potassium channel subunit of the KATP channels (P < .05).ConclusionAfter iatrogenic ischemia/reperfusion injury, urocortin expression in viable cells selectively colocalized with enhanced phosphorylation and mitochondrial relocation of protein kinase Cε, suggesting a cardioprotective role for endogenous urocortin. The physical interaction of activated protein kinase Cε with 6.1 inwardly rectifying potassium channel, enhanced by cardioplegic arrest, may represent a conjectural mechanism of urocortin-mediated cardioprotection.