Postischemic Function and Protein Kinase C Signal Transduction

Abstract

Background. The protective effects of myocardial preconditioning may occur by way of multiple mechanisms, with G-protein-mediated protein kinase C (PKC) translocation as a final common pathway. In this study we investigate the pharmacologic induction of preconditioning, by PKC translocation, using PKC agonists/antagonists to reveal its effects on contractile function after myocardial ischemia. Methods. Langendorff-perfused rabbit hearts received: (1) control; (2) dimethyl sulfoxide (vehicle); (3) acetylcholine (0.55 mmol/L; PKC agonist); (4) 1,2- s,n-dioctanoylglycerol (DOG; 22 mmol/L; PKC agonist); (5) chelerythrine (0.8 mmol/L; PKC antagonist); or (6) DOG–chelerythrine followed by a 2-hour ischemic period, using modified St. Thomas cardioplegia and a 45-minute reperfusion period. The period of ischemia was chosen so as to allow for improvement by appropriate agonists. To observe metabolic changes, tissue nucleotides and nucleosides were measured. Membrane and cytosolic fractions of PKC were determined by an anti-PKC antibody directed against the PKC δ isozyme. Lactate levels and myocardial pH were measured. Results. The PKC agonists DOG and acetylcholine showed the greatest recovery of developed pressure (68% ± 2%, 60% ± 9%, respectively). Although pH, lactate, and nucleotide levels were similar between groups at all times, myocyte PKC translocation demonstrated 25% of PKC δ isoforms on cell membrane sites during baseline, which shifted to 67% ± 17% with unprotected ischemia. DOG mimicked this shift with 58% ± 12% of PKC δ isoforms on membranes, which was also blocked by chelerythrine to 35% ± 7%. Conclusions. These data demonstrate that PKC translocation results in improved postischemic function, not by alteration of energetics or metabolism, and deserves further investigation.