Regulation of muscle cell Ca 2ϩ metabolism by 1,25-dihydroxy-vitamin D 3 [1,25(OH) 2 D 3 ] is mediated by the classic nuclear mechanism and a fast, nongenomic mode of action that activates signal transduction pathways. The role of individual protein kinase C (PKC) isoforms in the regulation of intracellular Ca 2ϩ levels ([Ca 2ϩ ] i ) by the hormone was investigated in cultured proliferating (myoblasts) and differentiated (myotubes) chick skeletal muscle cells. 1,25(OH) 2 D 3 (10 Ϫ9 M) induced a rapid (30-to 60-s) and sustained (Ͼ5-min) increase in [Ca 2ϩ ] i which was markedly higher in myotubes than in myoblasts. The effect was suppressed by the PKC inhibitor calphostin C. In differentiated cells, PKC activity increased in the particulate fraction and decreased in cytosol to a greater extent than in proliferating cells after 5-min treatment with 1,25(OH) 2 D 3 . By Western blot analysis, these changes were correlated to translocation of the PKC ␣ isoform from cytosol to the particulate fraction, which was more pronounced in myotubes than in myoblasts. Specific inhibition of PKC ␣ activity using antibodies against this isoform decreased the 1,25(OH) 2 D 3 -induced [Ca 2ϩ ] i sustained response associated with Ca 2ϩ influx through voltage-dependent calcium channels. Neomycin, a phospholipase C (PLC) inhibitor, blocked its effects on [Ca 2ϩ ] i , PKC activity, and translocation of PKC ␣. Exposure of myotubes to 1,2-dioleyl-rac-glycerol (1,2-diolein), also increased [Ca 2ϩ ] i , PKC activity, and the amount of PKC ␣ associated with the particulate fraction. Changes in [Ca 2ϩ ] i induced by diolein were inhibited by calphostin C and nifedipine. The results indicate that PKC ␣ activation via PLC-catalyzed phosphoinositide hydrolysis is part of the mechanism by which 1,25(OH) 2 D 3 regulates muscle intracellular Ca 2ϩ through modulation of the Ca 2ϩ influx pathway of the Ca 2ϩ response to the sterol.