We have studied the activation and inhibition of the mouse muscle adult-type nicotinic acetylcholine receptor by tetraethylammonium (TEA) and related quaternary ammonium derivatives. The data show that TEA is a weak agonist of the nicotinic receptor. No single-channel clusters were observed at concentrations as high as 5 mM TEA or in the presence of a mutation which selectively increases the efficacy of the receptor. When coapplied with 1 mM carbamylcholine (CCh), TEA decreased the effective opening rate demonstrating that it acts as a competitive antagonist of CCh-mediated activation. Kinetic analysis of currents elicited by CCh and TEA allowed an estimate of receptor affinity for TEA of about 1 mM, while an upper limit of 10 s−1 could be set for the wild-type channel-opening rate constant for receptors activated by TEA alone. At millimolar concentrations, TEA inhibited nicotinic receptor currents by depressing the single-channel amplitude. The effect had an IC50 of 2–3 mM, depending on the conditions of the experiment, and resembled a standard open-channel block. However, the decrease in channel amplitudes was not accompanied by an increase in the mean burst duration, indicating that a linear open-channel blocking mechanism is not applicable. Upon studying block by other nicotinic receptor ligands it was found that block by CCh, tetramethylammonium and phenyltrimethylammonium can be accounted for by the sequential blocking mechanism while block in the presence of methyltriethylammonium, ethyltrimethylammonium or choline was inconsistent with such a mechanism. A mechanism in which receptors blocked by TEA can close would account for the experimental findings.
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机译:我们已经研究了四乙铵(TEA)和相关的季铵衍生物对小鼠肌肉成年型烟碱乙酰胆碱受体的激活和抑制作用。数据显示,TEA是烟碱受体的弱激动剂。在浓度高达5 mM TEA或存在选择性增加受体功效的突变的情况下,未观察到单通道簇。当与1 mM氨甲酰胆碱(CCh)共同使用时,TEA降低了有效开放速率,表明它是CCh介导的激活的竞争性拮抗剂。通过对CCh和TEA引发的电流进行动力学分析,可以估计受体对TEA的亲和力约为1 mM,而野生型通道开放率的上限可以设置为10 s -1 sup>对于仅由TEA激活的受体恒定。在毫摩尔浓度下,TEA通过降低单通道振幅来抑制烟碱样受体电流。取决于实验条件,该效应的IC50为2-3 mM,类似于标准的明渠模块。但是,信道幅度的减小并没有伴随着平均突发持续时间的增加,这表明线性开放信道阻塞机制不适用。在研究了其他烟碱受体配体的阻滞作用后,发现顺式阻滞机理可解释为CCh,四甲基铵和苯基三甲基铵的阻滞作用,而在甲基三乙基铵,乙基三甲基铵或胆碱存在下的阻滞作用与这种机理不一致。实验发现可能是由TEA阻断的受体可以关闭的机制。
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