title: Muscarinic receptor stimulated GTPase activity in synaptic membranes from bovine retina.
abstract: GTPase activity has been measured in synaptic membranes from bovine retina, with and without muscarinic receptor stimulation. Maximal stimulation above basal levels was achieved with 5 microM oxotremorine and 100 microM carbachol. (4-Hydroxy-2-butynyl)-1-trimethylammonium m-chlorocarbanilate chloride, which is selective for the M1 muscarinic receptor, failed to stimulate GTPase activity. 4-Diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) inhibition of oxotremorine stimulation demonstrated the presence of two populations of receptors, a low-affinity site (IC50 +/- SEM, 0.63 +/- 0.18 microM) which accounted for 63% of the inhibition and a high-affinity site (IC50 less than 1 nM) which accounted for the remaining 37%. When carbachol-stimulated GTPase activity was assayed, a single 4-DAMP inhibitory site was apparent (IC50 +/- SEM, 2.0 +/- 0.9 microM). Pirenzepine inhibited GTPase activity at a single site (IC50 values +/- SEM, 46.9 +/- 11 and 25.4 +/- 6.5 microM against oxotremorine and carbachol, respectively). Methoctramine was equipotent against carbachol and oxotremorine stimulation (IC50 values, 4.2 +/- 1.8 and 6.2 +/- 1.5 microM). Inhibition of maximal carbachol and oxotremorine stimulation by muscarinic antagonists at the major site had a rank order of potency of 4-DAMP = methoctramine greater than pirenzepine. Thus, the major site for muscarinic stimulation of GTPase activity in bovine retinal membranes is pharmacologically similar to M2 receptors.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: H
authors.initials: H
authors.lastname: McIntosh
authors.forename: C
authors.initials: C
authors.lastname: Blazynski
mesh_terms: D000818:Animals; D002417:Cattle; D002855:Chromatography, Thin Layer; D003959:Diamines / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D020558:GTP Phosphohydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D018727:Muscarinic Antagonists; D010276:Parasympatholytics / Q000494:pharmacology; D010277:Parasympathomimetics / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D010890:Pirenzepine / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000502:physiology*; D012160:Retina / Q000201:enzymology*; D013268:Stimulation, Chemical; D013570:Synaptic Membranes / Q000201:enzymology*
chemical_list: D003959:Diamines; D018727:Muscarinic Antagonists; D010276:Parasympatholytics; D010277:Parasympathomimetics; D010880:Piperidines; D011976:Receptors, Muscarinic; D010890:Pirenzepine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; C054938:methoctramine