title: M3 muscarinic acetylcholine receptor coupling to PLC in rat exorbital lacrimal acinar cells.
abstract: This study was designed to characterize the muscarinic acetylcholine receptor (mAChR) subtype present in rat exorbital lacrimal gland as well as its biochemical coupling. The nonselective muscarinic antagonist [N-methyl-3H]scopolamine ([3H]NMS) binds with high affinity to a homogeneous population of binding sites in both membranes [dissociation constant (Kd) = 82.3 +/- 3.2 pM] and acinar cell (Kd = 170.3 +/- 20 pM) preparations. Muscarinic antagonist inhibition of [3H]NMS binding is homogeneous with the following order of potency: atropine > or = 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) > pirenzepine > 11-([2-(diethylamino)-ethyl]-1-piperidinyl)-acetyl- 5,11-dihydro-6H-pirido[2,3-b]1,4,benzo diazepine-6-one (AFDX 116). Both the affinity of the selective antagonists 4-DAMP, pirenzepine, and AFDX 116 and Northern blot analysis of lacrimal gland mRNAs show a single mAChR population of the M3 subtype. Muscarinic agonist inhibition of [3H]NMS binding displays both high (approximately 20%)- and low-affinity sites (approximately 80%). Both the receptor occupancy and the stimulation by agonists or the inhibition by antagonists of the accumulation of [3H]inositol phosphate were examined under identical conditions with respect to tissue preparations (acinar cells) and buffer (Krebs-Ringer). Results demonstrate 1) the efficient coupling of the M3 mAChR subtype with the phosphatidylinositol (4,5))bisphosphate-specific phospholipase C activity and 2) that the efficacy of a muscarinic agonist is dependent on its structure. Lastly, comparison of the agonists affinity and potency to trigger the [3H]inositol phosphate accumulation suggests that the occupation of the high-affinity agonist binding state of the M3 mAChR was involved in the cellular response.
authors.affiliation: Laboratoire de Biochimie des Transports Cellulaires, Centre National de la Recherche Scientifique, Unité de Recherche Associeé 1116, Université Paris-Sud, Orsay, France.
authors.forename: P
authors.initials: P
authors.lastname: Mauduit
authors.forename: H
authors.initials: H
authors.lastname: Jammes
authors.forename: B
authors.initials: B
authors.lastname: Rossignol
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D005260:Female; D007295:Inositol Phosphates / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D007765:Lacrimal Apparatus / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009116:Muscarine / Q000037:antagonists & inhibitors; D019832:N-Methylscopolamine; D010277:Parasympathomimetics / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000378:metabolism*; D012602:Scopolamine Derivatives / Q000037:antagonists & inhibitors / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D007295:Inositol Phosphates; D010277:Parasympathomimetics; D011976:Receptors, Muscarinic; D012602:Scopolamine Derivatives; D009116:Muscarine; D010738:Type C Phospholipases; D019832:N-Methylscopolamine