Application of a kinetic model to the apparently complex behavior of negative and positive allosteric modulators of muscarinic acetylcholine receptors

被引:42
作者
Avlani, V
May, LT
Sexton, PM
Christopoulos, A
机构
[1] Univ Melbourne, Dept Pharmacol, Parkville, Vic 3010, Australia
[2] Univ Melbourne, Howard Florey Inst Expt Physiol & Med, Parkville, Vic 3010, Australia
关键词
D O I
10.1124/jpet.103.059840
中图分类号
R9 [药学];
学科分类号
1007 ;
摘要
The binding of allosteric modulators to G protein-coupled receptors (GPCRs) is often described by an equilibrium allosteric ternary complex model (ATCM). This study evaluated the effects of three modulators on the binding of [H-3] N-methylscopolamine ([H-3] NMS) to the human M-2 muscarinic acetylcholine receptor ( mAChR). The binding of each modulator was more complex than predicted by the ATCM; the inhibitors heptane-1,7-bis-(dimethyl-3- phthalimidopropyl)-ammonium bromide and gallamine yielded biphasic curves that were described empirically by a two-site binding model, whereas the enhancer alcuronium yielded a bell-shaped curve. Radioligand dissociation assays revealed that the modulators retarded [H-3] NMS kinetics such that the system never attained equilibrium. Subsequent application of a kinetic ATCM accommodated and quantified all experimental observations. Our findings confirm and extend previous studies on the use of a kinetic ATCM for mAChR allosteric enhancers, but also highlight how complex curves displayed by allosteric inhibitors can be misinterpreted in terms of multisite orthosteric binding. It is possible that similar behavior of other allosteric modulators at GPCRs may reflect nonequilibrium binding artifacts rather than deviation from an ATCM.
引用
收藏
页码:1062 / 1072
页数:11
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