title: Alkaline phosphatase relieves desensitization of adenylate cyclase-coupled beta-adrenergic receptors in avian erythrocyte membranes.
abstract: Desensitization of adenylate cyclase-coupled beta-adrenergic receptors in avian erythrocytes results in a 40-65% decrease in agonist-stimulated adenylate cyclase activity and correlates with increased phosphorylation of beta-adrenergic receptors. To assess the role of phosphorylation in desensitization, membranes from isoprenaline- and dibutyryl cyclic AMP-desensitized turkey erythrocytes were incubated with alkaline phosphatase for 30 min at 37 degrees C, pH 8.0. In both preparations alkaline phosphatase treatment significantly decreased desensitization of agonist-stimulated adenylate cyclase activity by 40-75% (P less than 0.05). Similar results were obtained after alkaline phosphatase treatment of membranes from isoprenaline- and dibutyryl cyclic AMP-desensitized duck erythrocytes. Moreover, alkaline phosphatase treatment of membranes from duck erythrocytes desensitized with 12-O-tetradecanoylphorbol 13-acetate returned agonist-stimulated adenylate cyclase activity to near control values. In all experiments, inclusion of 20 mM-sodium phosphate to inhibit alkaline phosphatase during treatment of membranes attenuated the enzyme's effect on agonist-stimulated adenylate cyclase activity. In addition, alkaline phosphatase treatment of membranes from control and isoprenaline-desensitized turkey erythrocytes increased the mobility of beta-adrenergic-receptor proteins, specifically photoaffinity-labelled with [125I]iodocyanopindolol-diazirine, on SDS/polyacrylamide-gel electrophoresis. The increased mobility of the beta-adrenergic-receptor proteins after alkaline phosphatase treatment of membranes was again inhibited by 20 mM-phosphate. These results provide additional evidence for a direct role for phosphorylation in desensitization of adenylate cyclase-coupled beta-adrenergic receptors in avian erythrocytes.
authors.affiliation: Department of Molecular Pharmacology, Smith Kline and French Laboratories, Philadelphia, PA 19101.
authors.forename: J M
authors.initials: JM
authors.lastname: Stadel
authors.forename: R
authors.initials: R
authors.lastname: Rebar
authors.forename: S T
authors.initials: ST
authors.lastname: Crooke
mesh_terms: D000262:Adenylyl Cyclases / Q000097:blood*; D000469:Alkaline Phosphatase / Q000494:pharmacology*; D000818:Animals; D004372:Ducks; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D010710:Phosphates / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D014422:Turkeys
chemical_list: D010710:Phosphates; D011943:Receptors, Adrenergic, beta; D000469:Alkaline Phosphatase; D000262:Adenylyl Cyclases; D007545:Isoproterenol