PROTEIN-KINASE-C ACTIVATION BEFORE CARDIOPLEGIC ARREST - BENEFICIAL-EFFECTS ON MYOCYTE CONTRACTILITY

Objective: A potential intracellular mechanism for the protective effe cts of myocardial preconditioning is the activation of protein kinase C. The present study tested the hypothesis that a brief period of prot ein kinase C activation before cardioplegic arrest would provide prote ctive effects on myocyte contractility with subsequent reperfusion and rewarming. Methods: Left ventricular procine myocytes were assigned t o the following treatments: (1) Protein kinase C/cardioplegia: Protein kinase C activation in myocytes (n = 39) for 3 minutes with a phorbol ester (10(-9) mol/L of phorbol 12-myristate 13-acetate) in oxygenated , normothermic (37 degrees C) cell media. Protein kinase C activation was followed by 2 hours of cardioplegic arrest (K+, 24 mEq/L; HCO3-, 3 0 mEq/L; 4 degrees C) and a 5-minute reperfusion period (37 degrees C media). (2) Cardioplegia: Myocytes (n = 31), 2 hours of cardioplegic a rrest, and a 5-minute reperfusion and rewarming period. Myocyte contra ctility was measured by means of high-speed videomicroscopy. For compa rison purposes, contractile function was examined in myocytes (n = 70) under normothermic control conditions. Results: Myocyte shortening ve locity was reduced after cardioplegic arrest when compared with normot hermic values (22.3 +/- 1.6 vs 48.8 +/- 2.0 mu m/sec, p < 0.0001). Pro tein kinase C activation before cardioplegic arrest normalized myocyte shortening velocity (48.8 +/- 2.5 mu m/sec). Co-incubation with phorb ol 12-myristate 13-acetate and chelerythrine (10(-6) mol/L), an inhibi tor of protein kinase C, before cardioplegic arrest abolished the prot ective effects of phorbol 12-myristate 13-acetate pretreatment. Conclu sion: These results suggest that an endogenous means of providing impr oved myocardial protection during prolonged cardioplegic arrest can be achieved through a brief period of protein kinase C activation.