title: Phorbol ester inhibits phosphoinositide hydrolysis and calcium mobilization in cultured astrocytoma cells.
abstract: In cultured human 1321N1 astrocytoma cells, muscarinic receptor stimulation leads to phosphoinositide hydrolysis, formation of inositol phosphates, and mobilization of intracellular Ca2+. Treatment of these cells with 1 microM 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) completely blocks the carbachol-stimulated formation of [3H]inositol mono-, bis-, and trisphosphate ( [3H]InsP, [3H]InsP2, and [3H]InsP3). The concentrations of PMA that give half-maximal and 100% inhibition of carbachol-induced [3H]InsP formation are 3 nM and 0.5 microM, respectively. Inactive phorbol esters (4 alpha-phorbol 12,13-didecanoate and 4 beta-phorbol), at 1 microM, do not inhibit carbachol-stimulated [3H]InsP formation. The KD of the muscarinic receptor for [3H]N-methyl scopolamine is unchanged by PMA treatment, while the IC50 for carbachol is modestly increased. PMA treatment also abolishes carbachol-induced 45Ca2+ efflux from 1321N1 cells. The concomitant loss of InsP3 formation and Ca2+ mobilization is strong evidence in support of a causal relationship between these two responses. In addition, our finding that PMA blocks hormone-stimulated phosphoinositide turnover suggests that there may be feedback regulation of phosphoinositide metabolism through the Ca2+- and phospholipid-dependent protein kinase.
authors.forename: S A
authors.initials: SA
authors.lastname: Orellana
authors.forename: P A
authors.initials: PA
authors.lastname: Solski
authors.forename: J H
authors.initials: JH
authors.lastname: Brown
mesh_terms: D001254:Astrocytoma / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D006801:Humans; D006868:Hydrolysis; D010703:Phorbol Esters / Q000494:pharmacology*; D010704:Phorbols / Q000494:pharmacology*; D010716:Phosphatidylinositols / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D010703:Phorbol Esters; D010704:Phorbols; D010716:Phosphatidylinositols; D011976:Receptors, Muscarinic; C008876:phorbol-12,13-didecanoate; D002217:Carbachol; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; C033085:phorbol