Contrasting Effects of Allosteric and Orthosteric Agonists on M1 Muscarinic Acetylcholine Receptor Internalization and Down-regulation
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, arecolin...
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Veröffentlicht in: | The Journal of pharmacology and experimental therapeutics 2009-12, Vol.331 (3), p.1086-1095 |
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Zusammenfassung: | 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(1 H )-quinolinone (77-LH-28-1)] agonists on M 1 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 M 1 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 M 1 mACh receptor expression. Maximal phosphoinositide hydrolysis responses to the partial agonist arecoline were similar in
CHO-M 1 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 M 1 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. |
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ISSN: | 0022-3565 1521-0103 |
DOI: | 10.1124/jpet.109.160242 |