RESPONSE OF THE NEONATAL RAT CARDIOMYOCYTE IN CULTURE TO ENERGY DEPLETION - EFFECTS OF CYTOKINES, NITRIC-OXIDE, AND HEAT-SHOCK PROTEINS

Cytokines exert autocrine and paracrine effects on the heart, some of which may be mediated by inducible nitric oxide synthase (i-NOS) expre ssion. We studied the effects of cytokine-mediated NO synthesis on cel l injury in the presence of deoxyglucose (DOG) and cyanide (CV) (20 mM DOG and 2 mM CN) for up to 3 hours and during recovery (18 hours). Th e influence of heat shock protein-70 on the extent of myocyte damage w as also assessed. IL-1 beta and gamma-IFN act synergistically to enhan ce NO synthesis by cardiac myocytes. When these cytokines are present, the rate of ATP depletion after DOG and CN is significantly greater t han in their absence. When IL-1 beta and gamma-IFN are added with the NOS inhibitor, L-monomethyl-L-arginine (L-NMMA), or when a cytokine th at does not produce NO (TNF-alpha) is present, the rate of ATP depleti on is no different from the rate seen with DOG and CN alone. After rec overy for 18 hours, myocytes that were exposed to IL-1 beta and gamma- IFN release more lactic dehydrogenase and have significantly lower lev els of ATP. L-NMMA decreases lactic dehydrogenase release and maintain s ATP at levels similar to metabolically inhibited cells in the absenc e of these cytokines. Consistent with the decreased recovery in ATP wi th cells incubated with DOG and CN plus IL-1 beta and gamma-IFN is a d ecrease in cytochrome oxidase activity. Decreases in cellular ATP corr espond to increased levels of heat shock protein-70 measured in myocyt es after 18 hours of recovery after metabolic inhibition in the presen ce of IL-1 beta and gamma-IFN. In contrast, prior induction of heat sh ock protein-70 reduces the rate of ATP depletion in myocytes treated w ith DOG and CN and maintains ATP at levels that are significantly high er than those seen in non-heat-shocked cells. Recovery of cells expose d to heat shock is also greater, as seen by decreased lactic dehydroge nase and citrate synthase release. The heat-shocked myocytes contain s ignificantly more glycogen than the cells that were not heat shocked. The increased cellular glycogen is likely responsible for the greater lactate production and slower rates of ATP depletion in the heat-shock ed, metabolically inhibited cells. Cell survival under conditions of m etabolic inhibition is closely related to cellular ATP preservation.