Neuronal nicotinic alpha 7 receptor expressed in Xenopus oocytes presents five putative binding sites for methyllycaconitine
Neuronal nicotinic alpha 7 receptor expressed in Xenopus oocytes presents five putative binding sites for methyllycaconitine
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DOI：
10.1113/jphysiol.1996.sp021203
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发表时间：
1996-02-15
影响因子：
5.5
通讯作者：
Bertrand, D
中科院分区：
文献类型：
--
作者：
Palma, E;Bertrand, S;Bertrand, D
1.新近分离得到的化合物甲基乙叉乌头碱(MLA)是一种植物毒素，是烟碱型乙酰胆碱受体(NAChRs)的竞争性抑制物。我们发现，同分异构体α7受体对MLA表现出非常高的敏感性，其IC50在皮摩尔范围内。观察到该化合物对野生型5-羟色胺能受体(5-HT3)没有作用，而它是嵌合受体α7-5-HT3.3的强大拮抗剂，这加强了α7 MLA阻断的竞争性。MLA抑制野生型(WT)α7的时间过程遵循单调指数衰减，其时间常数与MLA浓度成正比，并可用双分子机制描述，向前速率常数(k(+))为2.7×10(7)S(-1)M(-1)。相反，从MLA抑制中恢复显示出与简单的双分子反应不相容的S形状的时间过程。鉴于神经元尼古丁受体的五聚体性质，提出了一个线性链模型，该模型包括5个与α7的同质性质相对应的假定的MLA结合位点。在假设单个MLA分子足以阻断受体功能的情况下，该模型充分描述了在α7野生型受体上获得的起始和恢复数据。对MLA阻断和重组异构体α4β2受体恢复的分析显示，正如预期的那样，只有一个与毒素的两个结合位点相容的时间过程，因此，进一步支持了我们模型的有效性。
1. The recently isolated compound methyllycaconitine (MLA) is a plant toxin which is a competitive inhibitor of nicotinic acetylcholine receptors (nAChRs). We found that homomeric alpha 7 receptors display a very high sensitivity to MLA with an IC50 in the picomolar range.2. The competitive nature of the alpha 7 MLA blockade was reinforced by the observation that this compound has no action on wild-type serotoninergic receptors (5-HT3), whereas it is a powerful antagonist of chimaeric receptors alpha 7-5-HT3.3. The time course of MLA inhibition of the wild-type (WT) alpha 7 follows a monotonic exponential decay whose time constant is proportional to the MLA concentration and could be described by a bimolecular mechanism with a forward rate constant (k(+)) of 2.7 x 10(7) s(-1) M(-1). In contrast, recovery from MLA inhibition displays an S-shaped time course that is incompatible with a simple bimolecular reaction.4. Given the pentameric nature of the neuronal nicotinic receptors, a linear chain model, including five putative MLA binding sites corresponding to the homomeric nature of alpha 7, is proposed.5. Both onset and recovery data obtained on the alpha 7 wild-type receptor are adequately described by this model assuming that a single MLA molecule is sufficient to block receptor function.6. analysis of MLA blockade and recovery of reconstituted heteromeric alpha 4 beta 2 receptors reveals, as expected, a time course compatible with only two binding sites for the toxin and, thus, further supports the validity of our model.