Release of enzymes from adult rat heart myocytes

The release of lactic dehydrogenase, creatine phosphokinase, and aspartate aminotransferase from initially viable, metabolically competent adult rat heart myocytes has been examined. Freshly isolated cells contain levels of total lactic dehydrogenase, creatine phosphokinase, and aspartate aminotransferase, as well as lactic dehydrogenase and creatine phosphokinase isoenzyme profiles that are quite comparable to those of intact heart tissue. When the cells are lysed with digitonin, 89% of total lactic dehydrogenase, but only 58% of creatine phosphokinase and 27% of aspartate aminotransferase are released. The retention of creatine phosphokinase by the digitonin-lysed cells is accounted for by complete retention of mitochondrial creatine phosphokinase and 20% of MM-creatine phosphokinase. When intact myocytes are incubated under anoxic, substrate-deprived conditions, there is a gradual loss of the three enzymes to the suspending medium and a parallel increase in the fraction of the cells permeable to trypan blue. The fraction of freely soluble cytoplasmic enzymes lost was equivalent to the fraction of the cells permeable to the dye over a wide range of viability (17-95% viable by dye exclusion criteria), but permeable cells retained mitochondrial creatine phosphokinase and particulate aspartate aminotransferase. These results suggest that simultaneous and complete release of soluble cytoplasmic enzymes occurs as each individual cell sustains sarcolemmal damage.