Changes in the protein kinase C activity or rat sternomastoid muscle during development and after denervation

The relationship between the activity of protein kinase C (PKC) and muscle innervation was explored in the rat sternomastoid muscle (SM) from day 18 of gestation (E18) to adult age. Between E18 and birth, PKC activity rose 5-fold, and during the day after birth, diminished to a level characteristic of the mature muscle. The rise chiefly occurred in the neural part of the muscle, in both the membrane and the cytosol fractions. Between E18 and day 5 after birth, the ratios of membrane to cytosol PKC activity rose from 0.5 to 10 and 3 respectively in the neural and aneural parts of the muscle. Denervation of adult SM reduced PKC activity by half in the membrane fraction of the neural part but did not significantly change it in the membrane or cytosol fractions of the aneural parts. These results suggest that innervation plays an important part in determining the level of PKC activity in muscle.