title: Mepacrine blocks beta-adrenergic agonist-induced desensitization in astrocytoma cells.
abstract: C6 astrocytoma cells contain beta-adrenergic receptors coupled to adenylate cyclase. A 2-hr exposure to l-isoproterenol results in an 80% decrease in cyclic AMP production in response to a subsequent challenge by l-isoproterenol (desensitization). This loss in responsiveness is paralleled by a 20-30% decrease in the apparent number of beta-adrenergic receptors and by increased release of arachidonic aciid into the medium. The increased release of arachidonic acid is caused by the action of phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) and corresponds to increased turnover of methylated phospholipids. Mepacrine and tetracaine, both inhibitors of this phospholipase A2, are able to block l-isoproterenol-induced desensitization of cyclic AMP production and the decrease in beta-adrenergic receptors. Mellitin and phorbol ester, two activators of phospholipase A2, when preincubated with the cells cause a decreased cyclic AMP response of the cells to l-isoproterenol. These results suggest that the activation of phospholipase A2 in the local domain of the beta-adrenergic receptor may be involved in desensitization.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism; D001254:Astrocytoma; D002478:Cells, Cultured; D007545:Isoproterenol / Q000037:antagonists & inhibitors*; D008555:Melitten / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors; D054467:Phospholipases A2; D011796:Quinacrine / Q000494:pharmacology*; D051381:Rats; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000378:metabolism; D013748:Tetracaine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D001095:Arachidonic Acids; D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D013748:Tetracaine; D008555:Melitten; D010741:Phospholipases A; D054467:Phospholipases A2; D000262:Adenylyl Cyclases; D011796:Quinacrine; D007545:Isoproterenol; D013755:Tetradecanoylphorbol Acetate