The effect of the PKC inhibitor calphostin C and the PKC agonist phorbol 12-myristate 13-acetate on regulation of cytosolic Ca(2+) in mammalian skeletal muscle cells.
Protein kinase C (PKC) has been shown to exert broad actions in modulating Ca(2+) in cardiac myocytes, however, the effect of PKC in skeletal muscle cells is largely unknown. In this study, we examined the effect of the PKC inhibitor calphostin C (CC) and the PKC agonist phorbol 12-myristate 13-acetate (PMA) on intracellular Ca(2+) handling in C2C12 skeletal myotubes and skinned skeletal muscle fibers of the rat. CC (250 nM) significantly prolonged (P=0.01, n=6), and the PKC agonist PMA (500 nM; P=0.03, n=6) significantly shortened the decay phase of electrically induced Ca(2+) transients in C2C12 myotubes without affecting the amplitude or the time to peak of the transients. Skinned fiber studies showed that CC significantly inhibits SR Ca(2+) uptake in skeletal muscle cells. PMA had no effect. CC also increased the peak of ATP-induced Ca(2+) transients release by 94.2% (P<0.0001) in the presence of extracellular Ca(2+) and 54.5% (P=0.04) without external Ca(2+) via IP(3)-Ca(2+) release pathway in C2C12 myotubes, while PMA had no effect, suggesting that CC may modulate IP(3)-induced Ca(2+) release via a PKC-independent mechanism. CC at a concentration of 1 microM was able to induce a large sustained elevation in basal [Ca(2+)](i) that was blocked by Ca(2+) store depletion and the IP(3) receptor blocker 2-APB. These results indicate that PKC plays a role in modulation of SR function in skeletal muscle cells, and the PKC inhibitor CC may alter Ca(2+) handling via both PKC-dependent and PKC-independent pathways.
Han
Renzhi
R
Physiology, School of Biomedical and Chemical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. renzhi-han@uiowa.edu
Bakker
Anthony J
AJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002460:Cell Line; D003600:Cytosol / Q000187:drug effects* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000633:toxicity*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D009281:Naphthalenes / Q000633:toxicity*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity*
D004791:Enzyme Inhibitors; D009281:Naphthalenes; D011493:Protein Kinase C; C058819:calphostin C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium