HOMOMERIC AND NATIVE ALPHA-7 ACETYLCHOLINE-RECEPTORS EXHIBIT REMARKABLY SIMILAR BUT NONIDENTICAL PHARMACOLOGICAL PROPERTIES, SUGGESTING THAT THE NATIVE RECEPTOR IS A HETEROMERIC PROTEIN COMPLEX

Sucrose gradient analysis of chick acetylcholine receptor (AChR) alpha7 subunits expressed in oocytes indicates that they form pharmacologically active homomers of the same size as native alpha7 AChRs, a size compatible with a complex of five alpha7 subunits. By immunoisolating the [S-35]methionine-labeled alpha7 subunits we also demonstrate that they do not appear to assemble with endogenous Xenopus AChR subunits. Pharmacological characterization of detergent-solubilized brain alpha7 AChRs and alpha7 homomers reveals that they have similar but nonidentical properties. The pharmacological difference is most accentuated for cytisine (approximately 50-fold). Thus, at least in E18 chicken brain, most or all of the native alpha7 AChRs do not appear to be homomeric.