Partial deletion of the nicotinic cholinergic receptor alpha 4 or beta 2 subunit genes changes the acetylcholine sensitivity of receptor-mediated 86Rb+ efflux in cortex and thalamus and alters relative expression of alpha 4 and beta 2 subunits.

alpha 4 and beta 2 nicotinic cholinergic receptor (nAChR) subunits can assemble in heterologous expression systems as pentameric receptors with different subunit stoichiometries that exhibit differential sensitivity to activation by acetylcholine, yielding biphasic concentration-effect curves. nAChR-mediated Rb-86(+) efflux in mouse brain synaptosomes also displays biphasic acetylcholine (ACh) concentration-response curves. Both phases are mediated primarily by alpha 4 beta 2*-nAChR, because deletion of either the alpha 4 or beta 2 subunit reduces response at least 90%. A relatively larger decrease in the component of Rb-86(+) efflux with lower ACh sensitivity occurred with partial deletion of alpha 4 (alpha 4(+/-)), whereas a larger decrease in the component with higher ACh sensitivity was elicited by partial deletion of beta 2 (beta 2(+/-)). Immunoprecipitation with selective antibodies demonstrated that more than 70% of [H-3] epibatidine binding sites in both regions contained only alpha 4 and beta 2 subunits. Subsequently, alpha 4 and beta 2 subunit content in the cortex and thalamus of alpha 4 and beta 2 wild types and heterozygotes was analyzed with Western blots. Partial deletion of alpha 4 decreased and partial deletion of beta 2 increased the relative proportion of the alpha 4 subunit in assembled receptors. Although these methods do not allow exact identification of stoichiometry of the subtypes present in wild-type cortex and thalamus, they do demonstrate that cortical and thalamic nAChRs of the alpha 4(+/-) and beta 2(+/-) genotypes differ in relative expression of alpha 4 and beta 2 subunits a result that corresponds to the relative functional changes observed after partial gene deletion. These results strongly suggest that alpha 4 beta 2-nAChR with different stoichiometry are expressed in native tissue