The subunit composition and pharmacology of α-Conotoxin MII-binding nicotinic acetylcholine receptors studied by a novel membrane-binding assay

The subunit composition and pharmacology of a-Conotoxin MII-binding (alpha-CtxMII) nicotinic acetylcholine receptors (nAChR) was studied by an improved [I-125]-alpha-CtxMII membrane binding method. This binding method facilitates pharmacological studies that have been difficult to accomplish with [I-125]-a-CtxMII autoradiography or alpha-CtxMII inhibition of [I-125]-epibatidine binding. Binding densities and K-d-values obtained by this [I-125]-alpha-CtXMII membrane binding were similar to the values obtained by autoradiography or alpha-CtxMII inhibition of [I-125]-epibatidine binding, verifying that each of these approaches measures the same nAChR population. Binding results with nAChR subunit-null mutant mice confirm and extend observations from earlier studies: [I-121]-alpha-CtxMII binding measures two sets of alpha 6 beta 2* nAChR (alpha 4 alpha 6 beta 2 beta 3 or alpha 6 beta 2 beta 3). Most nicotinic agonists and antagonists show monophasic inhibition of [I-125]-alpha-CtxMII binding, indicating that alpha 4 alpha 6 beta 2 beta 3 and alpha 6 beta 2 beta 3 have similar binding properties. Comparison of the binding and activation profiles of alpha 6 beta 2* nAChR to those of other nAChR subtypes (alpha 4 beta 2* and beta 4*) indicates that these receptors have distinctly different pharmacology indicating that it may be possible to target alpha 6 beta 2* nAChR selectively to develop compounds that might be therapeutically useful. (c) 2005 Elsevier Ltd. All rights reserved.