Developmental changes in contractile protein adenosine 5'-triphosphatase in the rabbit heart.

This study was designed to investigate developmental changes in contractile protein adenosine 5'-triphosphatase in the rabbit heart. Myofibrils and myosin were isolated from ventricular muscles from the fetal, newborn, and adult rabbits. Actin and troponin-tropomyosin complex were isolated from the adult skeletal muscle. Myofibrillar (actomyosin) adenosine 5'-triphosphatase measured at low ionic strength increased with development. In contrast, myofibrillar calcium adenosine 5'-triphosphatase at high ionic strength was the greatest in the newborn and the lowest in the adult. Myosin calcium adenosine 5'-triphosphatase and actin-activated myosin adenosine 5'-triphosphatase were also the greatest in the newborn and the lowest in the adult. The relative proportion of myosin isozyme V1 was the greatest in the newborn and the lowest in the adult. The addition of troponin-tropomyosin complex stimulated myosin adenosine 5'-triphosphatase in the presence of calcium in the adult, but not in the newborn and fetus. As a result, actin-activated myosin adenosine 5'-triphosphatase in the presence of troponin-tropomyosin complex was the greatest in the adult, followed by the newborn and fetus. These data suggest that the low myofibrillar adenosine 5'-triphosphatase activity at low ionic strength in the premature heart may be due to the age-related difference in the interaction of myosin with troponin-tropomyosin. Developmental change in myosin calcium adenosine 5'-triphosphatase (which is determined by the relative proportion of isomyosin V1 and V3) may not be directionally identical to that of the physiologically important myofibrillar adenosine 5'-triphosphatase.