Activation and block of mouse muscle-type nicotinic receptors by tetraethylammonium
Activation and block of mouse muscle-type nicotinic receptors by tetraethylammonium
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DOI：
10.1113/jphysiol.2003.043885
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发表时间：
2003-08-15
影响因子：
5.5
通讯作者：
Steinbach, JH
中科院分区：
文献类型：
--
作者：
Akk, G;Steinbach, JH
研究了四乙基铵（TEA）及其季铵盐衍生物对小鼠肌肉烟碱型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时，未观察到单通道簇。当与1 mM氨甲酰胆碱（CCh）共同应用时，TEA降低了有效的开放率，表明它作为CCh介导的激活的竞争性拮抗剂。由CCh和TEA引起的电流的动力学分析允许对TEA的受体亲和力的估计为约1 mM，而对于单独由TEA激活的受体，野生型通道开放速率常数的上限可设定为10 s（-1）。在毫摩尔浓度下，TEA通过抑制单通道幅度来抑制烟碱受体电流。该效应的IC 50为2-3 mM，取决于实验条件，类似于标准的开放通道阻断。然而，通道振幅的降低并不伴随着平均猝发持续时间的增加，这表明线性开放通道阻滞机制不适用。在研究通过其他烟碱受体配体的阻断时，发现通过CCh、四甲基铵和苯基三甲基铵的阻断可以通过顺序阻断机制来解释，而在甲基三乙基铵、乙基三甲基铵或胆碱存在下的阻断与这种机制不一致。一种被TEA阻断的受体可以关闭的机制可以解释实验结果。
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.