Abstract

We examined α7β2-nicotinic acetylcholine receptor (α7β2-nAChR) expression in mammalian brain and compared pharmacological profiles of homomeric α7-nAChR and of α7β2-nAChR. α-Bugarotoxin affinity purification or immunoprecipitation with anti-α7 subunit antibodies (Abs) were used to isolate nAChR containing α7 subunits from rat or human brain samples. α7β2-nAChR were detected in forebrain, but not other tested regions, from both species, based on western blot analysis of isolates using β2 subunit-specific Abs. Abs 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 (α7)_5-, (α7)₄(β2)_1-, and (α7)₃(β2)_2-nAChR was confirmed using two-electrode voltage-clamp recording of responses to nicotinic ligands. Importantly pharmacological profiles were indistinguishable for concatenated (α7)_5-nAChR or for homomeric α7-nAChR constituted from unlinked α7 subunits. Pharmacological profiles were similar for (α7)_5-, (α7)₄(β2)_1-, and (α7)₃(β2)_2-nAChR except for diminished efficacy of nicotine (normalized to acetylcholine efficacy) at α7β2- vs. α7-nAChR. This study represents the first direct confirmation of α7β2-nAChR expression in human and mouse forebrain, supporting previous mouse studies that suggested relevance of α7β2-nAChR in Alzheimer's disease etiopathogenesis. These data also indicate that α7β2-nAChR subunit isoforms with different α7:β2 subunit ratios have similar pharmacological profiles to each other, and to α7 homopentameric nAChR. This supports the hypothesis that α7β2-nAChR agonist activation predominantly or entirely reflects binding to α7/α7 subunit interface sites.