DELAYED PRECONDITIONING OF CULTURED ADULT-RAT CARDIAC MYOCYTES - ROLEOF 70-KDA AND 90-KDA HEAT-STRESS PROTEINS

We investigated the protective effect of heat stress and metabolic pre conditioning in cultured adult rat cardiac myocytes and correlated thi s effect with induction of heat shock proteins (HSP). Myocytes were pr econditioned with sublethal heat shock or metabolic preconditioning fo r 30 min. Twenty hours later, preconditioned myocytes were subjected t o lethal heat shock (46 degrees C for 2 h) or ischemia by incubation i n ischemic buffer for 2 h. Cellular injury index was reduced from 69 /- 4.0% in lethally heat-shocked cells to 27.0 +/- 1.6% with heat shoc k preconditioning (mean +/- SE; P < 0.01) and 19.0 +/- 3.0% with metab olic preconditioning (P < 0.01). Cellular injury index was 81.0 +/- 1. 0% in ischemic myocytes and was reduced to 25.9 +/- 2.7 and 21.4 +/- 2 .6% in heat shock- and metabolic-preconditioned myocytes, respectively (P < 0.01). A significant cross-tolerance of myocytes against lethal injury was observed with the two preconditioning methods. Western blot analysis revealed 3.3- and 2.5-fold increases in HSP 90 and 500- and 15-fold increases in HSP 70 with heat shock and metabolic precondition ing, respectively. HSP 27 expression remained unaltered relative to co ntrol cells. We conclude that heat shock and metabolic preconditioning induce delayed tolerance against lethal injuries in adult cardiac myo cytes with elevated levels of HSP 70 and HSP90.