Isoenzyme pattern and activity of myocardial creatine phosphokinase under heart adaptation to prolonged overload

Three isoenzymes of creatine phosphokinase (CPK) were detected in rat heart myocardium after electrophoretic separation of the enzyme in agarose gel: MM isozyme, MB isozyme and BB isozyme. The ratio of their activities was 60:30:5. Total activity of CPK per unit mass of myocardium was increased concomitant with transformation of its isoenzyme spectrum during the early stage of heart adaptation to the increased loading caused by aortic constriction. By the third day of cardiac hyperfunction, relative BB isozyme activity in the heart had increased to 15%, relative activity of the hybrid MB isozyme was increased to 40%, and relative activity of the main muscle MM isozyme was decreased to 45%. The relative increase in the activity of BB isozyme appears to reflect a preference for accumulation of the most functionally effective, short-lived isoenzymes-which play the key role in adaptation of tissues and systems to long-term loading.