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Title: Contrasting Effects of Allosteric and Orthosteric Agonists on M1 Muscarinic Acetylcholine Receptor Internalization and Down-regulation
Authors: Thomas, Rachel L.
Langmead, Christopher J.
Wood, Martyn D.
Challiss, R.A. John
First Published: Dec-2009
Publisher: American Society for Pharmacology and Experimental Therapeutics (ASPET)
Citation: Journal of Pharmacology and Experimental Therapeutics, 2009, 331 (3), pp. 1086-1095.
Abstract: A new class of subtype-selective muscarinic acetylcholine (mACh) receptor agonist that activates the receptor through interaction at a site distinct from the orthosteric acetylcholine binding site has been reported recently. Here, we have compared the effects of orthosteric (oxotremorine-M, arecoline, pilocarpine) and allosteric [4-n-butyl-1-[4-(2-methylphenyl)-4-oxo-1-butyl] piperidine (AC-42); 1-[3-(4-butyl-1-piperidinyl)propyl]-3,4-dihydro-2(1H)-quinolinone (77-LH-28-1)] agonists on M1 mACh receptor internalization and down-regulation, as well as functional coupling in a Chinese hamster ovary (CHO) cell line. In contrast to full and partial orthosteric agonists, which cause significant receptor internalization and down-regulation, prolonged exposure to AC-42 did not significantly alter either cell-surface or total cellular M1 mACh receptor expression. 77-LH-28-1, an AC-42 homolog, did cause some receptor internalization, but not down-regulation. The presence of atropine completely prevented the orthosteric agonist-induced adaptive changes in receptor populations; however, in contrast, the copresence of atropine and AC-42 significantly increased both cell-surface receptor and total M1 mACh receptor expression. Maximal phosphoinositide hydrolysis responses to the partial agonist arecoline were similar in CHO-M1 cells pretreated for 24 h with either AC-42 or vehicle; in contrast, these responses were markedly reduced when cells were pretreated with oxotremorine-M or pilocarpine. These data indicate that, whereas AC-42 binding to the M1 mACh receptor can initiate signal transduction, the AC-42-liganded receptor is resistant to the usual mechanisms regulating receptor internalization and down-regulation. In addition, our data suggest unusual interactions between allosteric agonists and orthosteric antagonists to regulate cell-surface and total cellular receptor expression.
ISSN: 0022-3565
Type: Article
Description: This paper was published as Journal of Pharmacology and Experimental Therapeutics, 2009, 331 (3), pp. 1086-1095. It is available from Doi: 10.1124/jpet.109.160242
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Appears in Collections:Published Articles, Dept. of Cell Physiology and Pharmacology

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