The Novel a 7 b 2-Nicotinic Acetylcholine Receptor Subtype Is Expressed in Mouse and Human Basal Forebrain : Biochemical and Pharmacological Characterization s

We examined a7b2-nicotinic acetylcholine receptor (a7b2nAChR) expression in mammalian brain and compared pharmacological profiles of homomeric a7-nAChRs and a7b2-nAChRs. a-Bungarotoxin affinity purification or immunoprecipitation with anti-a7 subunit antibodies (Abs) was used to isolate nAChRs containing a7 subunits from mouse or human brain samples. a7b2-nAChRs were detected in forebrain, but not other tested regions, from both species, based on Western blot analysis of isolates using b2 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 (a7)5-, (a7)4(b2)1-, and (a7)3(b2)2-nAChRs was confirmed using two-electrode voltage clamp recording of responses to nicotinic ligands. Importantly, pharmacological profiles were indistinguishable for concatenated (a7)5-nAChRs or for homomeric a7-nAChRs constituted from unlinked a7 subunits. Pharmacological profiles were similar for (a7)5-, (a7)4(b2)1-, and (a7)3(b2)2-nAChRs except for diminished efficacy of nicotine (normalized to acetylcholine efficacy) at a7b2versus a7-nAChRs. This study represents the first direct confirmation of a7b2-nAChR expression in human and mouse forebrain, supporting previous mouse studies that suggested relevance of a7b2-nAChRs in Alzheimer disease etiopathogenesis. These data also indicate that a7b2-nAChR subunit isoforms with different a7/b2 subunit ratios have similar pharmacological profiles to each other and to a7 homopentameric nAChRs. This supports the hypothesis that a7b2-nAChR agonist activation predominantly or entirely reflects binding to a7/a7 subunit interface sites.