The novel alpha7beta2-nicotinic acetylcholine receptor subtype is expressed in mouse and human basal forebrain: biochemical and pharmacological characterization.

We examined alpha7beta2-nicotinic acetylcholine receptor (alpha7beta2-nAChR) expression in mammalian brain and compared pharmacological profiles of homomeric alpha7-nAChRs and alpha7beta2-nAChRs. alpha-Bungarotoxin affinity purification or immunoprecipitation with anti-alpha7 subunit antibodies (Abs) was used to isolate nAChRs containing alpha7 subunits from mouse or human brain samples. alpha7beta2-nAChRs were detected in forebrain, but not other tested regions, from both species, based on Western blot analysis of isolates using beta2 subunit-specific Abs. Ab specificity was confirmed in control studies using subunit-null mutant mice or cell lines heterologously expressing specific human nAChR subtypes and subunits. Functional expression in Xenopus oocytes of concatenated pentameric (alpha7)5-, (alpha7)4(beta2)1-, and (alpha7)3(beta2)2-nAChRs was confirmed using two-electrode voltage clamp recording of responses to nicotinic ligands. Importantly, pharmacological profiles were indistinguishable for concatenated (alpha7)5-nAChRs or for homomeric alpha7-nAChRs constituted from unlinked alpha7 subunits. Pharmacological profiles were similar for (alpha7)5-, (alpha7)4(beta2)1-, and (alpha7)3(beta2)2-nAChRs except for diminished efficacy of nicotine (normalized to acetylcholine efficacy) at alpha7beta2- versus alpha7-nAChRs. This study represents the first direct confirmation of alpha7beta2-nAChR expression in human and mouse forebrain, supporting previous mouse studies that suggested relevance of alpha7beta2-nAChRs in Alzheimer disease etiopathogenesis. These data also indicate that alpha7beta2-nAChR subunit isoforms with different alpha7/beta2 subunit ratios have similar pharmacological profiles to each other and to alpha7 homopentameric nAChRs. This supports the hypothesis that alpha7beta2-nAChR agonist activation predominantly or entirely reflects binding to alpha7/alpha7 subunit interface sites.