ACTIVITY OF CARDIO-SPECIFIC ISOENZYMES OF CREATINE-PHOSPHOKINASE AND LACTATE-DEHYDROGENASE IN MONOLAYER-CULTURES OF NEONATAL RAT-HEART CELLS

Monolayer cultures of neonatal rat heart cells, prepared according to Harary and Farley [12], contain, besides muscle cells (myoblasts, myocytes), a number of non-muscle cells (fibroblasts, endothelial cells) proliferating at a faster rate than the muscle cells. In ageing cultures of this type changes in enzyme and isoenzyme activities have been reported. These activity shifts have been interpreted either as an adaptation to hypoxic conditions, or as inherent to ageing of muscle cells. In this study we determined the changes in time of the activity of creatine phosphokinase including its isoenymes MM, MB and BB, and the activity of lactate dehydrogenase (LDH) including the isoenzyme combinations LDH1+2 and LDH3+4+5. It is shown that for creatine phosphokinase and its isoenzymes as well as for lactate dehydrogenase and its isoenzymes the activity changes in time are compatible with the hypothesis, that the isoenzyme shifts are the result of a change in the proportion of muscle cells in the culture, rather than an adaptation to hypoxia or ageing of the muscle cells. It is also demonstrated that inhibition of cell proliferation, by using a nutrient medium without serum, prevents the occurrence of these activity shifts. © 1979.