Myosin adenosine triphosphatase activity during work-induced growth of slow and fast skeletal muscle in the normal rat.

The influence of work-induced hypertrophy on the myosin of skeletal muscle was studied. Unilateral tenotomy of the gastrocnemius muscle (single tenotomy procedure) in normal rats led to rapid compensatory growth of the synergistic plantaris and soleus muscles. Total myosin increased with hypertrophy. The myosin from these hypertrophied muscles, however, was enzymatically and structurally identical to the myosin from the contralateral limb muscles. Tenotomy of the plantaris in addition to the gastrocnemius (double tenotomy procedure) caused more rapid hypertrophy of the soleus than that observed with the single tenotomy procedure. The specific activity of the myosin ATPase from these hypertrophied soleus muscles was 11% lower (p < 0.05) than that of the myosin from the controls. However, the alkali stability of the ATPase activity and the light chain content of the myosin from the control and hypertrophied soleus muscles were identical. Thus, only the specific activity of the myosin ATPase accumulated in the soleus muscle during work-induced growth appears to depend on the rate of muscle hypertrophy. Preliminary studies on adult soleus, plantaris, and newborn rat muscle myosin showed that the decrease in specific activity of the hypertrophied soleus myosin ATPase cannot be explained by the selective accumulation of fast muscle or fetal muscle myosin.