Abstract 2318: Selective Mitochondrial Translocation of Phosphorylated PKCε in Viable Myocytes Overexpressing Urocortin after Cardioplegic Arrest and Reperfusion: Physical Interaction of Phosphorylated PKCε with the Kir6.1 Cardiac Potassium Channel Subunit as a Potential Mechanism of Cardioprotection
Cardioplegic arrest and subsequent reperfusion inevitably expose the heart to an iatrogenic ischemia/reperfusion injury (iIRI). We previously reported that iIRI caused myocyte induction of urocortin, an endogenous cardioprotective peptide. This study investigates in patients undergoing cardiac surgery the cardioprotective role and the mechanism of action of Ucn, with respect to PKCε expression, activation and relocation. Two 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. In hearts exposed to iIRI, induction of Ucn was documented both at the mRNA (255% of basic levels; p < 0.05) and protein level (four-fold increase; p < 0.01). iIRI also induced a selective increase of PKC-ε mRNA (225% of internal control; p < 0.05) and a two-fold overexpression of total PKCε (p < 0.05), which paralleled a 2.9-fold increase in PKCε phosphorylation (p < 0.01). Mitochondrial translocation of activated PKCε was only observed in post-cardioplegic samples, using both subcellular fractionation (p < 0.05) and immunostaining techniques (p < 0.05). Importantly, enhanced PKCε/mitochondria colocalization was selectively observed in viable myocytes, showing concurrently positive staining for urocortin (p < 0.05). Finally, co-immunoprecipitation experiments documented an iIRI-enhanced physical interaction of phosphorylated PKCε with the Kir6.1 subunit of the KATP channels (p < 0.05). Following iIRI, urocortin expression in viable cells selectively colocalized with enhanced phosphorylation and mitochondrial relocation of PKCε, suggesting a cardioprotective role for endogenous Ucn. The physical interaction of activated PKCε with Kir6.1, enhanced by cardioplegic arrest, may represent a conjectural mechanism of urocortin-mediated cardioprotection.