Briggs Clark A, Gubbins Earl J, Marks Michael J, Putman C Brent, Thimmapaya Rama, Meyer Michael D, Surowy Carol S
Neuroscience Research, R47W Bldg. AP9A-3, Abbott Laboratories, 100 Abbott Park Rd., Abbott Park, IL 60064, USA.
Mol Pharmacol. 2006 Jul;70(1):227-40. doi: 10.1124/mol.105.020198. Epub 2006 Mar 28.
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.
α4β2烟碱型乙酰胆碱受体（nAChRs）被认为是大脑中主要的尼古丁结合位点。重组α4β2 nAChR表现出与低EC50和高EC50成分的双相浓度-反应关系。本研究表明，非翻译区（UTR）可影响α4β2和α3β2 nAChR高敏感性亚型的表达。注射缺乏UTR的α4和β2 RNA的卵母细胞对乙酰胆碱表现出双相浓度-反应关系，高敏感性EC50值为0.5至2.5微摩尔（占群体的14 - 24%），低敏感性EC50值为110至180微摩尔（占群体的76 - 86%）。相比之下，含有UTR的信使RNA仅表达高敏感性α4β2 nAChR亚型，其乙酰胆碱EC50值为2.2微摩尔。进一步的研究揭示了高敏感性和低敏感性α4β2亚型之间的药理学差异。虽然拮抗剂二氢β-刺桐啶（IC50为3 - 6纳摩尔）和甲基lycaconitine（IC50为40 - 135纳摩尔）对高敏感性和低敏感性α4β2没有选择性，但氯异吲哚铵、美加明和d-筒箭毒碱分别对乙酰胆碱低敏感性的α4β2亚型有100倍、8倍和5倍的选择性。相反，鉴定出了在效力和效能方面选择性激活高敏感性α4β2亚型的激动剂。此外，其中两种激动剂被证明可激活小鼠脑α4β2以及在非洲爪蟾卵母细胞中表达的雪貂高敏感性α4β2。通过使用含UTR的RNA，还实现了新型高敏感性α3β2 nAChR的特异性表达。这些研究1）为α4β2 nAChR多种亚型的存在提供了进一步证据，2）将其扩展到α3β2 nAChR，3）证明UTR对含β2的nAChR特性的影响，4）揭示了以亚型选择性方式与α4β2相互作用的化合物。
