Boorman James P, Beato Marco, Groot-Kormelink Paul J, Broadbent Steven D, Sivilotti Lucia G
Department of Pharmacology, The School of Pharmacy, 29/39 Brunswick Square, London, WC1N 1AX United Kingdom.
J Biol Chem. 2003 Nov 7;278(45):44033-40. doi: 10.1074/jbc.M211719200. Epub 2003 Aug 11.
We compared the main properties of human recombinant alpha3beta4beta3 neuronal nicotinic receptors with those of alpha3beta4 receptors, expressed in Xenopus oocytes. beta3 incorporation decreased the channel mean open time (from 5.61 to 1.14 ms, after approximate correction for missed gaps) and burst length. There was also an increase in single channel slope conductance from 28.8 picosiemens (alpha3beta4) to 46.7 picosiemens (alpha3beta4beta3; in low divalent external solution). On the other hand, the calcium permeability (determined by a reversal potential method in chloride-depleted oocytes) and the pharmacological properties of beta3-containing receptors differed little from those of alpha3beta4. The main pharmacological difference in alpha3beta4beta3 "triplet" receptors was a 3-fold decrease in the potency of lobeline relative to acetylcholine. Nevertheless, there was no change in the rank order of potency for agonists (epibatidine >> lobeline > cytisine, 1,1-dimethyl-4-phenylpiperazinium iodide, nicotine > acetylcholine > carbachol for both receptors; measured at low agonist concentrations). Sensitivity to the competitive antagonists trimetaphan (0.2-1 microM) and dihydro-beta-erythroidine (30 microM) was similar for the two combinations, with a Schild KB for trimetaphan of 76 and 66 nM on alpha3beta4 and alpha3beta4beta3, respectively. The change in single channel conductance confirms that beta3 replaces a beta4 subunit in the pentamer. The absence of pronounced differences in the pharmacological profile of the triplet receptor argues against a role for the beta3 subunit in the formation of agonist binding sites, whereas the changes in channel kinetics suggest an important effect on receptor gating. The shortening of the burst length of beta3-containing receptors implies that any synaptic currents mediated by such channels would have faster decay kinetics.
我们比较了在非洲爪蟾卵母细胞中表达的人重组α3β4β3神经元烟碱型受体与α3β4受体的主要特性。β3的掺入降低了通道的平均开放时间（经对漏记间隙进行近似校正后，从5.61毫秒降至1.14毫秒）和爆发长度。单通道斜率电导也有所增加，从28.8皮西门子（α3β4）增至46.7皮西门子（α3β4β3；在低二价外部溶液中）。另一方面，含β3受体的钙通透性（通过在氯离子缺失的卵母细胞中采用反转电位法测定）和药理特性与α3β4受体的差异不大。α3β4β3“三联体”受体的主要药理差异在于，相对于乙酰胆碱，洛贝林的效力降低了3倍。然而，激动剂的效价顺序没有变化（两种受体在低激动剂浓度下测定时，埃博霉素>>洛贝林>金雀花碱、碘化1,1 - 二甲基 - 4 - 苯基哌嗪、烟碱>乙酰胆碱>卡巴胆碱）。两种组合对竞争性拮抗剂曲美芬（0.2 - 1微摩尔）和二氢β - 刺桐碱（30微摩尔）的敏感性相似，曲美芬在α3β4和α3β4β3上的Schild KB分别为76和66纳摩尔。单通道电导的变化证实β3在五聚体中取代了一个β4亚基。三联体受体药理特征没有明显差异，这表明β3亚基在激动剂结合位点形成中不起作用，而通道动力学的变化表明其对受体门控有重要影响。含β3受体爆发长度的缩短意味着由这类通道介导的任何突触电流将具有更快的衰减动力学。
