title: Desensitization of muscarinic M1 receptors of murine neuroblastoma cells (clone N1E-115) without receptor down-regulation and protein kinase C activity.
abstract: Acute desensitization of M1 muscarinic receptor-mediated responses (cyclic GMP formation and inositol phosphate release) was studied in murine neuroblastoma cells (N1E-115 clone). After a 45-min incubation at 37 degrees of N1E-115 cells either in monolayer or in suspension, with the muscarinic agonist carbachol (1 mM), the receptor-mediated cyclic GMP response to carbachol was nearly completely lost. This loss was associated with greater than 80% loss of carbachol-mediated inositol phosphate release. The protein kinase C activator phorbol 12-myristate 13-acetate (PMA) inhibited both responses with similar potencies. Carbachol or PMA reduced by 30-40% the number of muscarinic receptor sites for antagonist and agonist on intact cells (determined in binding assays using [3H]N-methylscopolamine) only for cells in monolayer and not for those in suspension. PMA but not carbachol pretreatment of cells in monolayer or in suspension caused a translocation of [3H]phorbol 12,13-dibutyrate binding and protein kinase C activity. In addition, desensitization to carbachol occurred in cells largely depleted of protein kinase C by chronic exposure to PMA. Thus, agonist-mediated down-regulation is not needed for muscarinic M1 receptor desensitization, which may be a result of the activation of a receptor-activated kinase different from protein kinase C.
authors.affiliation: Department of Psychiatry, Mayo Foundation, Rochester, MN 55905.
authors.forename: S
authors.initials: S
authors.lastname: Kanba
authors.forename: K S
authors.initials: KS
authors.lastname: Kanba
authors.forename: M
authors.initials: M
authors.lastname: McKinney
authors.forename: M
authors.initials: M
authors.lastname: Pfenning
authors.forename: R
authors.initials: R
authors.lastname: Abraham
authors.forename: S
authors.initials: S
authors.lastname: Nomura
authors.forename: L
authors.initials: L
authors.lastname: Enloes
authors.forename: S
authors.initials: S
authors.lastname: Mackey
authors.forename: E
authors.initials: E
authors.lastname: Richelson
mesh_terms: D000818:Animals; D002217:Carbachol / Q000378:metabolism / Q000494:pharmacology*; D015536:Down-Regulation / Q000187:drug effects; D006157:Guanosine Monophosphate / Q000096:biosynthesis; D007295:Inositol Phosphates / Q000378:metabolism; D051379:Mice; D019832:N-Methylscopolamine; D009447:Neuroblastoma / Q000201:enzymology / Q000378:metabolism*; D010276:Parasympatholytics / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000378:metabolism; D012602:Scopolamine Derivatives / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D007295:Inositol Phosphates; D010276:Parasympatholytics; D011976:Receptors, Muscarinic; D012602:Scopolamine Derivatives; D006157:Guanosine Monophosphate; D002217:Carbachol; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D019832:N-Methylscopolamine