Effect of muscular activity on the turnover rate of actin and myosin heavy and light chains in different types of skeletal muscle. I. Changes in the turnover rate of myosin and actin during and after single-bout physical activity.

During a single-bout of 6-h swimming, myosin heavy chain (HC) and actin in m. gastrocnemius turned over more slowly than they did in the pre-exercise period, whereas the turnover rate of myosin light chain (LC) increased; 48 h after swimming, actin and myosin HC had a significantly higher turnover rate, but the turnover rate of myosin LC remained at the pre-exercise level. Exercise caused a remarkable decrease in the incorporation of the 14C leucine into actin and myosin HC, but an increase in the incorporation into myosin LC. An elevation of the synthesis rate of actin and myosin HC was observed 48 h after exercise. Myofibrillar proteinase activity at alkaline pH reached its maximum level during exercise, but the same was observed for the proteolytic activity at acid pH 6 h and at neutral pH 24 h after exercise.