Acid and alkaline proteolytic activities of cast-immobilized rat hind-limb muscles after electric stimulation

Abstract

The activities of cathepsin D (CD), beta-glucuronidase (beta-GU), alkaline protease (AKP), and the rate of acid autolysis (AA) were measured in gastrocnemius, soleus, and tibialis anterior muscles of the rat after bilateral cast immobilization in the middle position for one and three weeks. The effects of daily indirect electric stimulation on the proteolytic activities of immobilized muscles were also studied. In gastrocnemius and tibialis anterior, electric stimulation partially prevented the loss of muscle weight after immobilization for one week. Activities of CD and beta-GU were highest in the soleus, but the activities did not change therein after immobilization or electric stimulation. In gastrocnemius, the activities of CD and AKP and the AA rate increased significantly after immobilization. Electric stimulation during immobilization seemed to prevent the increase of CD and AKP activities significantly after one (CD) and three (AKP) weeks immobilization. In tibialis anterior, the activities of CD and AKP and the AA rate increased significantly in the stimulated muscles after immobilization for three weeks. Both in the gastrocnemius and tibialis anterior the beta-GU activity increased significantly in the stimulated muscles. The results suggest that during the disuse atrophy process and electric stimulation of immobilized muscles, rat hind-limb muscles differ in acid and alkaline proteolytic responses.