Amelioration of denervation-induced atrophy by clenbuterol is associated with increased PKC-alpha activity

Rat soleus muscle was denervated for 3 or 7 days, and total membrane protei n kinase C (PKC) activity and translocation and immunocytochemical localiza tion of PKC isoforms were examined. Dietary administration of clenbuterol c oncomitant with denervation ameliorated the atrophic response and was assoc iated with increased membrane PKC activity at both 3 (140%) and 7 (190%) da ys. Of the five PKC isoforms (alpha, epsilon, theta, zeta, and mu) detected in soleus muscle by Western immunoblotting, clenbuterol treatment affected only the PKC-alpha and PKC-theta forms. PKC-alpha was translocated to the membrane fraction upon denervation, and the presence of clenbuterol increas ed membrane-bound PKC-alpha and active PKC-alpha as assayed by Ser(657) pho sphorylation. PKC-theta protein was downregulated upon denervation, and tre atment with clenbuterol further decreased both cytosolic and membrane level s. Immunolocalization of PKC-theta showed differences for regulatory and ca talytic domains, with the latter showing fast-fiber type specificity. The r esults suggest potential roles of PKC-alpha and PKC-theta in the mechanism of action of clenbuterol in alleviating denervation-induced atrophy.