title: Muscarinic M3 receptors mediate total inositol phosphates accumulation in murine HSDM1C1 fibrosarcoma cells.
abstract: Muscarinic receptors in murine fibrosarcoma HSDM1C1 cells were characterized using both radioligand binding and total inositol phosphates accumulation (IPs). Muscarinic agonists elicited a concentration-dependent enhancement of IPs accumulation with a maximum of 14-fold stimulation above basal level. The following potencies (-log EC50) were observed for the full agonists: (+)-cis-dioxolane 5.4, oxotremorine-M 5.3, (+)-muscarine 5.2 and carbachol 5.0. Bethanechol (4.1) and arecoline (5.0) were partial agonists, evoking 43 and 55%, respectively of the maximum level of stimulation to (+)-cis-dioxolane, whereas pilocarpine and McN-A-343 were inactive as agonists (1 mumol/l-1 mmol/1). The apparent affinities for muscarinic antagonists (-log KB) estimated by Schild regression were: 4-DAMP (4-diphenylacetoxy-N-methylpiperidine methiodide) 9.2, dicyclomine 7.0, pirenzepine 6.9, (+/-)-p-F-HHSiD (para-fluoro-hexahydro-siladifenidol) 7.0, AF-DX 116 6.2, methoctramine 5.7. In saturation binding studies using [3H]N-methylscopolamine a homogeneous population of sites was identified, with a density of 145 pmol/mg protein. In competition radioligand binding studies, the following apparent affinities (-log Ki) were observed: 4-DAMP 9.7, dicyclomine 8.3, (+/-)-p-F-HHSiD 7.6, AF-DX 116 6.8, methoctramine 6.6 and gallamine 6.8. In binding studies all antagonists studied recognized a single population of sites, as judged by the Hill coefficients from the displacement isotherms. These data are consistent with HSDM1C1 cells expressing an apparent homogeneous muscarinic M3 population that mediates a large level of total IPs accumulation. This clonal line may provide a useful model to further elucidate relationship between endogenous muscarinic M3 receptor stimulation and IPs accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Institute of Pharmacology, Syntex Discovery Research, Palo Alto, CA 94304.
authors.forename: R M
authors.initials: RM
authors.lastname: Eglen
authors.forename: N A
authors.initials: NA
authors.lastname: Sharif
authors.forename: Z P
authors.initials: ZP
authors.lastname: To
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002217:Carbachol / Q000494:pharmacology; D004148:Dioxolanes / Q000494:pharmacology; D005354:Fibrosarcoma; D007295:Inositol Phosphates / Q000378:metabolism*; D051379:Mice; D009116:Muscarine / Q000494:pharmacology; D018727:Muscarinic Antagonists; D019832:N-Methylscopolamine; D010095:Oxotremorine / Q000494:pharmacology; D010276:Parasympatholytics / Q000494:pharmacology; D010277:Parasympathomimetics / Q000494:pharmacology; D010890:Pirenzepine / Q000378:metabolism; D011869:Radioligand Assay; D011976:Receptors, Muscarinic / Q000502:physiology*; D012602:Scopolamine Derivatives / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D004148:Dioxolanes; D007295:Inositol Phosphates; D018727:Muscarinic Antagonists; D010276:Parasympatholytics; D010277:Parasympathomimetics; D011976:Receptors, Muscarinic; D012602:Scopolamine Derivatives; D010890:Pirenzepine; D010095:Oxotremorine; D009116:Muscarine; D002217:Carbachol; D019832:N-Methylscopolamine