Modulation of the structure‐binding relationships of antagonists for muscarinic acetylcholine receptor subtypes

Abstract

1Membranes from rat cerebral cortex, myocardium and extraorbital lacrimal gland were used as sources of M1, M2 and M3 muscarinic acetylcholine receptors respectively and the affinities of seven antagonists for the three subtypes were examined under different experimental conditions. 2 The affinities for the membrane-bound receptors were measured at different ionic strengths and temperatures and compared with those determined on the receptor solubilised in the neutral detergent digitonin or the zwitterionic detergent, CHAPSO. 3 The range of measured affinity constants of a given antagonist for a specific subtype varied from 2 (atropine at M1 receptors) to 1000 (AF-DX 116 at M2 receptors). 4 As a consequence of these changes in affinity, which were dependent on the drug, the subtype and the experimental conditions, both the structure-binding relationships of a given subtype can

Binding of Orthosteric Ligands to the Allosteric Site of the M2Muscarinic Cholinergic Receptor

“…They apparently are not caused by magnesium, and the reported effects of ionic strength on the affinity of gallamine are comparatively small (Pedder et al, 1991). They may be related to the state of aggregation of the receptor, which can exist as oligomers in whole cells (Goin and Nathanson, 2006), in detergent-solubi- The data represented in Fig.…”

Allosteric Modulation of the Cannabinoid CB1 Receptor

“…At the moment, the basis for this discrepancy between functional and binding affinity estimates remains unknown. However, a previous study by Pedder et al (1991) revealed a striking divergence in the affinity estimates of the allosteric modulator, gallamine, at M 2 muscarinic receptors depending on the assay conditions used to determine this value. Indeed, differences in the affinity of the modulator spanned almost two orders of magnitude.…”

“…Indeed, differences in the affinity of the modulator spanned almost two orders of magnitude. It is also worth noting that these same variations in assay conditions had minimal effects on orthosteric ligand affinity estimates (Pedder et al, 1991). Because allosteric sites are, by their very nature, topographically distinct from the orthosteric site on a GPCR, they can be sensitive to ionic changes under conditions where orthosteric ligands are minimally affected.…”

Interactions of Orthosteric and Allosteric Ligands with [3H]Dimethyl-W84 at the Common Allosteric Site of Muscarinic M2 Receptors

“…The low-affinity saturable component was also present in centrifugation assays using M 2 CHO cell membranes (data not shown) and is therefore not a specific characteristic of porcine heart membranes. Figure 2B also (Pedder et al, 1991;Trä nkle et al, 1996). The results of the equilibrium and kinetic assays are shown in Fig.…”