Untranslated region-dependent exclusive expression of high-sensitivity subforms of alpha4beta2 and alpha3beta2 nicotinic acetylcholine receptors.

alpha4beta2 nicotinic acetylcholine receptors (nAChRs) are recognized as the principal nicotine binding site in brain. Recombinant alpha4beta2 nAChR demonstrate biphasic concentration-response relationships with low- and high-EC50 components. This study shows that untranslated regions (UTR) can influence expression of high-sensitivity subforms of alpha4beta2 and alpha3beta2 nAChR. Oocytes injected with alpha4 and beta2 RNA lacking UTR expressed biphasic concentration-response relationships for acetylcholine with high-sensitivity EC50 values of 0.5 to 2.5 microM (14-24% of the population) and low-sensitivity EC50 values of 110 to 180 microM (76-86%). In contrast, message with UTR expressed exclusively the high-sensitivity alpha4beta2 nAChR subform with an acetylcholine EC50 value of 2.2 microM. Additional studies revealed pharmacological differences between high- and low-sensitivity alpha4beta2 subforms. Whereas the antagonists dihydro-beta-erythroidine (IC50 of 3-6 nM) and methyllycaconitine (IC50 of 40-135 nM) were not selective between high- and low-sensitivity alpha4beta2, chlorisondamine, mecamylamine, and d-tubocurarine were, respectively, 100-, 8-, and 5-fold selective for the alpha4beta2 subform with low sensitivity to acetylcholine. Conversely, agonists that selectively activated the high-sensitivity alpha4beta2 subform with respect to efficacy as well as potency were identified. Furthermore, two of these agonists were shown to activate mouse brain alpha4beta2 as well as the ferret high-sensitivity alpha4beta2 expressed in Xenopus laevis oocytes. With the use of UTR-containing RNA, exclusive expression of a novel high-sensitivity alpha3beta2 nAChR was also achieved. These studies 1) provide further evidence for the existence of multiple subforms of alpha4beta2 nAChR, 2) extend that to alpha3beta2 nAChR, 3) demonstrate UTR influence on beta2-containing nAChR properties, and 4) reveal compounds that interact with alpha4beta2 in a subform-selective manner.