Alteration of myofibrillar ATPase activities in hearts of cardiomyopathic hamsters (BIO 53.58)

Abstract

Purified myofibrils were prepared from cardiac muscle of normal (RB) and cardiomyopathic (BIO 53.58) hamsters at the age of 24 to 160 days. Myofibrils from normal hamsters were sensitive to increasing concentrations of calcium buffered with EGTA. As the free calcium concentration rose from 0.1 to 10μ m, the ATPase activity increased from 0.06 to 0.35 μmol/mg/min. The free calcium concentration for half-maximal myofibrillar ATPase activity was found to be 1 × 10 −6 m. The myofibrillar ATPase activities from male and female normal hamsters did not vary with age. However, the fractions from cardiomyopathic hamsters behaved differently according to their sex. The maximal myofibrillar ATPase from the female cardiomyopathic hamsters (24- to 30-day-old) was less than that of the normal, but increased greatly at 36 days of age. At 44 days of age, the female myofibrillar ATPase activity was again depressed. The myofibrillar ATPase of the male cardiomyopathic hamsters was slightly increased at 36 days of age. At 44 days, the male hamsters exhibited a slight decrease in the myofibrillar ATPase activity. At 50 days of age, myofibrillar ATPase activities from both male and female cardiomyopathic hamsters were found to be depressed; this decrease was also observed at 91 days in the male and 161 days in the female animals. The free calcium concentration for the half-maximal myofibrillar ATPase activity was found to be unchanged in all the cardiomyopathic hamsters studied.