Cardiopulmonary Bypass with Cardioplegic Arrest Activates Protein Kinase C in the Human Myocardium

BackgroundThe protein kinase C (PKC) family consists of 12 isoforms, 6 of which have been found in human myocardium (PKCα, βI/βII, δ, ε, η, and λ/ι). These kinases function in regulation of contractility, ion channels, and in cellular protection or damage during ischemia-reperfusion injury. This study investigated the effects of controlled ischemia-reperfusion injury through cardioplegic arrest on PKC activity in patients undergoing cardiac surgery.Study DesignMyocardium and skeletal muscle were harvested from patients before and after cardiopulmonary bypass and cardioplegic arrest. Total PKC (n = 12) was isolated and specifically, the PKCδ (n = 8) and PKCε (n = 8) isoforms were immunoprecipitated for use in functional kinase assays. Cellular fractions (n = 4) were separated by differential ultracentrifugation and analyzed by Western blotting for membrane translocation (an indirect indicator of increased activity). Immunofluorescent staining for PKCδ and PKCε was performed on myocardial sections. An in vitro assay of hypoxic cardioplegic arrest followed by reoxygenation was performed using isolated cardiomyocytes, and apoptosis was assessed.ResultsCardioplegic arrest was associated with a 24.4% ± 4.6% increase (p < 0.05) in total PKC activity, a 26.7% ± 4.9% increase (p < 0.05) in PKCδ activity, and a 35.3% ± 14% increase (p < 0.05) in PKCε activity in myocardium. Cardioplegic arrest induced migration of PKCδ and ε to the z-line of the cardiomyocyte. Inhibition of PKCδ in the in vitro studies demonstrated a considerable reduction in apoptotic cells.ConclusionsPKCδ and ε have previously been shown to mediate and protect, respectively, from ischemia-reperfusion injury after myocardial ischemia. Demonstration of increases in their activity after cardioplegic arrest provides support for their possible role in myocardial function after cardiac surgery. Isoform-specific modulators may be of potential therapeutic value in treating postoperative myocardial dysfunction.