Long-term wash-resistant effects of brief interaction of xanomeline at the M1 muscarinic receptor

[摘要] Compared to other M, 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 1 h 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 [H-3]N-methylscopolamine ([H-3]NMS) to intact cells. Shortening the xanomeline pretreatment period to 1 min had the same trends as the 1 h 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, receptor-xanomeline complex between states that vary in their ability to bind [H-3]NMS. However, possible involvement of other mechanisms of long-term receptor regulation cannot be discounted. (c) 2006 Elsevier Ireland Ltd. All rights reserved.

[发布日期] 2006-12-13

[关键词] xanomeline;wash-resistant binding;muscarinic receptors;allosteric modulation