Increased phosphorylation of nuclear protein in myonuclei isolated from denervated skeletal muscle

The slow-twitch soleus muscle of the rat hindlimb was denervated by cutting the sciatic nerve in the midthigh on one side. A sham operation was performed on the contralateral side to provide a control soleus muscle. At 24, 48, 72, and 120 hours after these surgical procedures, the animals were sacrificed and the nuclei which were isolated from these muscles incubated in a phosphorylating medium containing [gamma-32P]ATP. At the 48 hour denervation period only, the in vitro phosphorylation of TCA-precipitable nuclear proteins was significantly increased compared to control values. Resolution of the SDS-solubilized nuclear proteins by polyacrylamide gel electrophoresis revealed that the increased phosphorylation was more marked in some phosphoproteins than others. The significance of these early denervation changes are discussed with respect to increases in the activities of the nuclear RNA polymerases and changes in the phosphorylation of cytosolic protein.