Translocation of protein kinase C isoforms in rat muscle in response to fasting and refeeding.

Weanling rats were offered food ad libitum, or fasted for 18 h, or fasted and refed for times ranging from 5 to 30 min. Five protein kinase C (PKC) isoforms (alpha, epsilon, zeta, theta and mu) were detected in the hindlimb muscles by Western immunoblotting. PKC forms epsilon and theta were abundant in plantaris, but not in soleus muscle, and no difference in localization was detected between fed rats and those fasted for 18 h. PKC forms alpha and mu were affected by fasting and refeeding. PKC-mu was found only in the cytosolic fraction of the plantaris muscle of the fasted animal, but in the fully-fed animals it was also associated with the membrane fraction. The pattern of localization observed in the fully-fed state was restored in the fasted rats by 20 min refeeding. In contrast, PKC-alpha was not detected in the cytosolic fraction of the plantaris in fasted animals but rapidly reappeared there on refeeding, being restored to 20% and 80% of the fed value within 5 and 30 min of refeeding respectively. The timing of these changes was correlated with the increase in serum insulin concentration, which was significantly elevated above the fasted value by 5 min and at subsequent times. These data suggest a possible role for PKC isoforms alpha and mu in the metabolic changes that occur in skeletal muscle on transition between the fasted and the fed state.