Agonist and blocking actions of choline and tetramethylammonium on human muscle acetylcholine receptors
Agonist and blocking actions of choline and tetramethylammonium on human muscle acetylcholine receptors
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DOI：
10.1113/jphysiol.2009.176305
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发表时间：
2009-11-01
影响因子：
5.5
通讯作者：
Sivilotti, Lucia G.
中科院分区：
文献类型：
--
作者：
Lape, Remigijus;Krashia, Paraskevi;Sivilotti, Lucia G.
胆碱已广泛用作烟碱乙酰胆碱受体功能获得突变体研究的激动剂。它很有用，因为它的行为类似于部分激动剂。胆碱的功效很难测量，因为胆碱阻断通道的浓度比激活通道的浓度低约四倍。我们已经将激活机制安装到由胆碱和四甲基铵（TMA）从 HEK 表达的人重组肌肉烟碱受体引发的单通道活性中。激动剂的通道阻断被纳入所安装的机制中，并且发现阻断对于开放状态没有选择性。结果还表明，通道阻塞速度非常快，并且当阻塞者被绑定时，通道几乎可以像正常情况一样快速关闭。单通道数据与胆碱实际上是完全激动剂的机制兼容，其最大响应仅受通道阻滞的限制。然而，它们也与包含预开放构象变化（“翻转”）的机制兼容，其中胆碱是真正的部分激动剂。后一种解释受到浓度跳跃实验的支持，而且只有这种机制符合 TMA 数据。我们认为，胆碱与 TMA 一样，是一种部分激动剂，因为它在引发初始打开前构象变化方面非常无效（大约比乙酰胆碱低 600 倍）。一旦发生翻转，所有激动剂，甚至胆碱，都会以相似的效率打开通道。
Choline has been used widely as an agonist for the investigation of gain-of-function mutants of the nicotinic acetylcholine receptor. It is useful because it behaves like a partial agonist. The efficacy of choline is difficult to measure because choline blocks the channel at concentrations about four times lower than those that activate it. We have fitted activation mechanisms to single-channel activity elicited from HEK-expressed human recombinant muscle nicotinic receptors by choline and by tetramethylammonium (TMA). Channel block by the agonist was incorporated into the mechanisms that were fitted, and block was found not to be selective for the open state. The results also suggest that channel block is very fast and that the channel can shut almost as fast as normal when the blocker was bound. Single-channel data are compatible with a mechanism in which choline is actually a full agonist, its maximum response being limited only by channel block. However, they are also compatible with a mechanism incorporating a pre-opening conformation change ('flip') in which choline is a genuine partial agonist. The latter explanation is favoured by concentration jump experiments, and by the fact that only this mechanism fits the TMA data. We propose that choline, like TMA, is a partial agonist because it is very ineffective (approximately 600-fold less than acetylcholine) at eliciting the initial, pre-opening conformation change. Once flipping has occurred, all agonists, even choline, open the channel with similar efficiency.