Ca2+-activated protease in denervated rat skeletal muscle measured by an immunoassay

Right hind leg muscles of adult male rats were denervated by transecting the sciatic nerve, while muscles of the left leg served as a control. On days 4, 9, and 18 after denervation, the rats were killed and the extensor digitorum longus and soleus muscles removed. Extracts were prepared which contained the Ca2+-activated protease. The molecular weight of the protease in the extracts, measured immunologically on Western blots of SDS-polyacrylamide gels, was identical to that of purified standard protease and was unaffected by denervation. The amount of protease in each extract was measured by a solid phase immunoassay using monospecific IgG labeled with 125I, and the results were expressed as units of protease activity per milligram noncollagen protein. There were increases of 40 to 80% in the mean values obtained for both denervated muscles compared with controls. Because the protease is probably localized on the cell membrane, these modest increases are likely to be a consequence of a generalized over-development of muscle membranes which follows denervation.