title: Long-term wash-resistant effects of brief interaction of xanomeline at the M1 muscarinic receptor.
abstract: Compared to other M(1) muscarinic acetylcholine receptor (M(1) mAChR) agonists, xanomeline demonstrates both reversible and persistent modes of binding to the receptor. In our study, we investigated the long-term consequences of brief incubation of Chinese hamster ovary cells expressing M(1) mAChR (M(1)-CHO) with low concentrations of xanomeline followed by washing off the free drug. Thus, M(1)-CHO cells were exposed to 100 nM xanomeline for 1h then washed extensively. Washed cells were either used immediately for binding assays or incubated for 23 h in the absence of free xanomeline. Only the latter treatment conditions resulted in marked attenuation of binding of the muscarinic radioligand [(3)H]N-methylscopolamine ([(3)H]NMS) to intact cells. Shortening the xanomeline pretreatment period to 1 min had the same trends as the 1h pretreatment, implying that xanomeline binds instantly to the receptor to elicit long-term wash-resistant effects. Presence of atropine during the brief period of xanomeline pretreatment did not markedly modulate xanomeline's long-term effects, which suggests that persistent anchoring of the xanomeline molecule to the M(1) receptor takes place at a site distinct from the orthosteric binding domain. Our findings suggest the possibility of a time-dependent transition of the conformation of the muscarinic M(1) receptor-xanomeline complex between states that vary in their ability to bind [(3)H]NMS. However, possible involvement of other mechanisms of long-term receptor regulation cannot be discounted.
authors.affiliation: Division of Neuroscience Research in Psychiatry, University of Minnesota Medical School, Mayo Mail Code 392, 420 Delaware St. SE, Minneapolis, MN 55455, USA.
authors.forename: Kayla C
authors.initials: KC
authors.lastname: De Lorme
authors.forename: Krista L
authors.initials: KL
authors.lastname: Sikorski
authors.forename: Marianne K O
authors.initials: MK
authors.lastname: Grant
authors.forename: Esam E
authors.initials: EE
authors.lastname: El-Fakahany
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004347:Drug Interactions; D006801:Humans; D018721:Muscarinic Agonists / Q000494:pharmacology*; D018727:Muscarinic Antagonists / Q000494:pharmacology; D019832:N-Methylscopolamine / Q000493:pharmacokinetics; D011725:Pyridines / Q000494:pharmacology*; D043643:Receptor, Muscarinic M1 / Q000187:drug effects* / Q000378:metabolism*; D013830:Thiadiazoles / Q000494:pharmacology*; D013997:Time Factors; D014162:Transfection / Q000379:methods; D014316:Tritium / Q000493:pharmacokinetics
chemical_list: D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D011725:Pyridines; D043643:Receptor, Muscarinic M1; D013830:Thiadiazoles; D014316:Tritium; D001285:Atropine; C075257:xanomeline; D019832:N-Methylscopolamine