Cardioprotective Effect of Ischemic Preconditioning: Relationship between Intracellular Glycogen and Protein Kinase C

Abstract

Background:Recent studies suggest that the cardioprotective effect of ischemic preconditioning (IPC) is related to intracellular glycogen content in rat hearts, however, controversies still remain. Methods:To test this hypothesis, isolated Langendorff-perfused rabbit hearts were subjected to 45 min global ischemia followed by 120 min reperfusion with IPC (n=10) or without IPC (ischemic control, n=8). IPC was induced by one cycle of 5 min global ischemia and 10 min reperfusion. In the glucose (G)-free preconditioned group (n=10), G depletion-repletion was induced by perfusion with G-free Tyrode solution for 5 min and then G-containing Tyrode solution for 10 min followed by 45 min ischemia and 120 min reperfusion. For glycogen depletion or loading, hearts were treated with sodium acetate (NA, 5 mM, n=8) or insulin (Ins, 1 unit/L, n=8) for 15 min before 45 min ischemia. Left ventricular function and coronary flow (CF) were continuously recorded during experiments. Myocardial cytosolic and membrane protein kinase C (PKC) activities were measured by 32P-γATP incorporation into PKC-specific pepetide;glycogen content in the cardiac myocytes was determined by spectrophotometry with amyloglucosidase;expression of PKC isozymes was determined by Western blot with monoclonal antibodies. Infarct size was determined by staining with tetrazolium salt and planimetry. Data were analyzed by ANOVA and Tukey’s post-hoc test. Results:IPC or G-free preconditioning enhanced LV functional recovery;NA did not influence on functional recovery but Ins depressed it. Infarct size was significantly reduced by IPC, G-free preconditioning, and NA treatment (35.3±2.1% in the ischemic control, 18.7±1.2% in the IPC, 22.1±1.2% in the G-free preconditioned, 16.3±1.2% in the NA-treated group, and 32.8±1.6% in the Ins-treated group, p<0.05). Membrane PKC activities significantly increased by IPC, IPC and 45 min ischemia, G-free preconditioning, and G-free preconditioning and 45 min ischemia;especially, expression of membrane PKC-e increased by IPC and G-free preconditioning. Glycogen content decreased 논문접수일:2000년 10월 16일 심사완료일:2001년 1월 31일 교신저자:김호덕, 440-746 경기도 수원시 장안구 천천동 300 성균관대학교 의과대학 해부학교실 전화:(031) 299-6071·전송:(031) 299-6089 E-mail:hdkim@med.skku.ac.kr