The contractile apparatus of striated muscle in the course of atrophy and regeneration. II. Myosin and actin filaments in mature rat soleus muscle regenerating after reinnervation.

Changes in the contractile apparatus of denervated rat soleus muscles were investigated during the course of reinnervation. As observed earlier, in the course of denervation atrophy the ratio of myosin to actin filaments decreases because myosin filaments disappear faster than actin filaments (Jakubiec-Puka et al. 1981 a). After reinnervation the amount of myosin filaments and myosin heavy chains (myosin HC) in the muscle increased during the first few days; the increment of actin content was negligible. The proportion of myosin HC to actin remained lower than normal for about 30 days. The excess of actin filaments frequently observed in the newly-formed myofibrils reflects this disproportion. The results show a lability of myosin and suggest some cytoskeletal role for actin filaments.