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Differential Regulation of the M1 Muscarinic Acetylcholine Receptor by Orthosteric and Allosteric Ligands
Author(s) -
Thomas Rachel,
Langmead Christopher,
Wood Martyn,
Challiss John
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.727.10
Subject(s) - muscarinic acetylcholine receptor , pilocarpine , internalization , oxotremorine , muscarinic acetylcholine receptor m2 , chemistry , muscarinic acetylcholine receptor m5 , muscarinic acetylcholine receptor m3 , muscarinic acetylcholine receptor m1 , agonist , allosteric regulation , receptor , muscarinic acetylcholine receptor m4 , pharmacology , biochemistry , biology , neuroscience , epilepsy
AC‐42 (4‐ n ‐butyl‐1‐[4‐(2‐methylphenyl)‐4‐oxo‐1‐butyl] piperidine hydrogen chloride) is a selective M1 muscarinic receptor agonist with an allosteric mechanism of action. Here, we have investigated whether AC‐42 and two orthosteric muscarinic agonists (oxotremorine‐M (oxo‐M) and pilocarpine) cause internalization and down‐regulation of the M 1 muscarinic receptor. Oxo‐M (EC 50 0.8 μM) caused the greatest increase in [ 35 S]‐GTPγS‐Gα q/11 binding in membranes from Chinese hamster ovary cells stably expressing the M 1 muscarinic receptor, whereas AC‐42 (EC 50 1.6 μM) and pilocarpine (EC 50 2.4 μM) stimulated similar responses that were approx. 30% of the oxo‐M response. Using intact cell [ 3 H]‐NMS and [ 3 H]‐QNB binding assays, we next showed that after 24 h, oxo‐M (100 ìM) caused 68 ± 3% receptor internalization and 42 ± 3% receptor down‐regulation. Over a similar time‐course, pilocarpine (1 mM) caused 46 ± 7% internalization and 26 ± 8% down‐regulation. In contrast, AC‐42 did not cause significant receptor internalization or down‐regulation. These data suggest that while AC‐42 is able to activate selectively G q/11 ‐dependent signaling through the M 1 mACh receptor, it does not cause receptor internalization or down‐regulation, at least over the time‐course studied here.