title: Protein kinase C-activated calcium channel in the osteoblast-like clonal osteosarcoma cell line UMR-106.
abstract: The effects of protein kinase C stimulation on free cytosolic Ca2+ [( Ca2+]i) were studied in Fura 2-loaded UMR-106 cells. Stimulation of the protein kinase C with the tumor-promoting phorbol esters 12-O-tetradecanoylphorbol 13-acetate (TPA) and phorbol 12,13-diacetate or 1-oleoyl-2-acetylglycerol was followed by an increase in [Ca2+]i. The protein kinase C-induced increase in [Ca2+]i has a lag period, the duration of which was dependent on the stimulant and medium Ca2+ concentrations. With 2 microM TPA, the rise in [Ca2+]i peaked within 1.5 min, after which [Ca2+]i returned partially toward base line. The increase in [Ca2+]i was absolutely dependent on the presence of medium Ca2+ and was inhibited by the Ca2+ channel blockers nicardipine and verapamil. Cell stimulation also results in Ca2+ release from intracellular pool(s) which appears to be mediated by a Ca2+-dependent Ca2+ release mechanism. The reduction in [Ca2+]i was due to channel inactivation. Pretreatment of the cells with 1 nM TPA, 2 units/ml parathyroid hormone (PTH), or 15 microM forskolin blocked the effect of 2 microM TPA on [Ca2+]i. TPA and PTH were more potent inhibitors than was forskolin. The properties of this channel are compared to the cAMP-independent PTH-stimulated Ca2+ channel present in these cells.
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D010006:Osteoblasts / Q000378:metabolism*; D012516:Osteosarcoma; D010703:Phorbol Esters / Q000494:pharmacology; D011493:Protein Kinase C / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D007473:Ion Channels; D010703:Phorbol Esters; D005576:Colforsin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium