CHANGES IN SARCOLEMMAL AND SARCOPLASMIC-RETICULUM ATPASE ACTIVITIES WITH AGE IN CARDIOMYOPATHIC SYRIAN-HAMSTER

Sarcolemmal and sarcoplasmic reticular ATPase activities were studied in normal hamsters and in those with hereditary cardiomyopathy. These animals were studied at 30, 60, 120 and 200 days of age. Sarcoplasmic reticular ATPase activity in the normal hamster declined by 50% between 30 and 60 days of age, but in cardiomyopathic animals this fall was not seen until after 60 days of age. The final levels reached were identical in control and experimental animals. Sarcolemmal ATPase activity was constant at all ages studied in control animals, but was increased 2-fold between 60 and 120 days of age in cardiomyopathic animals and remained elevated at 200 days of age. This divergence in ATPase activity was interpreted as a functional dilution of the sarcoplasmic reticulum in cardiomyopathic hearts. This could be responsible for an imbalance of excitation and coupling, thus resulting in alterations in myocardial contractility.