title: Characterization of the subtype of muscarinic receptor coupled to the stimulation of phosphoinositide hydrolysis in 132-1N1 human astrocytoma cells.
abstract: Stimulation of muscarinic receptors increases phosphoinositide (PI) hydrolysis in 132-1N1 human astrocytoma cells. To evaluate the subtype of receptors which mediate PI hydrolysis in 132-1N1 cells, the effects of: a) the nonselective M1 agonist, carbachol; b) the selective M1 agonist, 4-hydroxy-2-butynyl-trimethylammonium chloride-m-chlorocarbinilate (McN-343); c) the nonselective antagonists, atropine and scopolamine; d) the relatively selective M1 antagonist, pirenzepine; e) the relatively selective M2 antagonists, AF-DX 116 (11-2-diethylaminomethyl-1-piperidinylacetyl-5, 11-dihydro-6H-pyrido-2,3-b-1,4-benzodiazepine-6-one) and methoctramine and f) the relatively selective M3 antagonist, hexahydrosila-difenidol (HHSiD) on PI hydrolysis in 132-1N1 cells were studied. The cell pools of inositol-phospholipids were prelabelled by incubating 132-1N1 cells in a low inositol containing medium (CMRL-1066) supplemented with [3H]inositol (2 microCi/ml) for 20-24 hours at 37 degrees C. The cells were washed and resuspended in a physiological salt solution, and PI hydrolysis was measured by accumulation of [3H]inositol-1-phosphate (IP) in the presence of 10 mM LiCl. Carbachol produced time and concentration dependent PI hydrolysis (EC50, 37 microM). McN-A343 did not cause significant hydrolysis of PI in 132-1N1 cells indicating that the receptor was not of M1 type. All the above muscarinic antagonists caused a concentration dependent decrease in the level of IP in response to carbachol (100 microM). The rank order of their affinities (pA2 values) was: atropine (8.8) > HHSiD (7.6) > pirenzepine (6.8) > methoctramine (6.0) > AF-DX 116 (5.8). This rank order supports the concept that M3 (other names, M2 beta, glandular M2) receptors are linked to PI hydrolysis in 132-1N1 cells. HHSiD, which is selective for M3 receptors of the smooth muscle has higher affinity for muscarinic receptors in 132-1N1 cells than AF-DX 116 which is selective for M2 receptors in cardiac tissue. If the receptor in 132-1N1 cells had been M2, part of the rank order for affinities would have been methoctramine > AF-DX 116 > HHSiD > pirenzepine. From all of these observations, the muscarinic receptor for PI hydrolysis in 132-1N1 cells is tentatively characterized as of M3 type.
mesh_terms: D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride / Q000494:pharmacology; D001254:Astrocytoma; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D003959:Diamines / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis; D010277:Parasympathomimetics / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology; D010890:Pirenzepine / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D012601:Scopolamine / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D003959:Diamines; D010277:Parasympathomimetics; D010716:Phosphatidylinositols; D010880:Piperidines; D011976:Receptors, Muscarinic; D010890:Pirenzepine; D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride; D001285:Atropine; D002217:Carbachol; D012601:Scopolamine; C046773:hexahydrosiladifenidol; C054938:methoctramine