Phorbol esters modulate the high Ca2(+)-stimulated accumulation of inositol phosphates in bovine parathyroid cells.
We examined the effects of TPA on the high Ca2(+)-stimulated accumulation of inositol phosphates in bovine parathyroid cells to determine whether protein kinase C modulates phosphoinositide turnover in a fashion similar to that observed in other cell types stimulated by more classic Ca2+ mobilizing hormones. Following exposure of parathyroid cells to TPA (10(-6) M) for 10 or 30 minutes, there was a time- and dose-dependent inhibition of the accumulation of inositol monophosphate (IP), inositol bisphosphate (IP2) and inositol trisphosphate (IP3) stimulated by 3 mM Ca2+. Half the maximal observed inhibition took place at 1-10 nM TPA, with 50-60% inhibition of high Ca2(+)-stimulated accumulation of inositol phosphates at 10(-6) M TPA. The active phorbol ester, 4 beta-phorbol didecanoate, produced similar effects; the inactive derivative, 4 alpha-phorbol didecanoate, was without effect. When parathyroid cells were exposed to TPA (10(-6) M) for varying times and were then incubated with high (3 mM) Ca2+, inhibition of inositol phosphate accumulation was observed with 10 or 30 minutes preincubation. In contrast, preincubation of cells with TPA for 3 or 18 h markedly enhanced the high (3 mM) Ca2(+)-induced increase in inositol phosphates. In cells preincubated with TPA for 18 h, binding sites for [3H]phorbol dibutyrate and total protein kinase C (PKC) activity were reduced by greater than 95% and by 71%, respectively, consistent with downregulation of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)
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Endocrine-Hypertension Unit, Brigham and Women's Hospital, Boston, MA 02115.
Congo
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Brown
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D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D002478:Cells, Cultured; D007295:Inositol Phosphates / Q000378:metabolism*; D010280:Parathyroid Glands / Q000187:drug effects* / Q000378:metabolism; D010703:Phorbol Esters / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D007295:Inositol Phosphates; D010703:Phorbol Esters; C008876:phorbol-12,13-didecanoate; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium