Rapid relief of block by mecamylamine of neuronal nicotinic acetylcholine receptors of rat chromaffin cells in vitro: An electrophysiological and modeling study
Rapid relief of block by mecamylamine of neuronal nicotinic acetylcholine receptors of rat chromaffin cells in vitro: An electrophysiological and modeling study
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DOI：
10.1124/mol.58.4.778
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发表时间：
2000-10-01
影响因子：
3.6
通讯作者：
Nistri, A
中科院分区：
文献类型：
--
作者：
Giniatullin, RA;Sokolova, EM;Nistri, A
在全细胞膜片钳记录的大鼠嗜铬细胞上，研究了甲氨基甲胺对神经元型烟碱型乙酰胆碱受体(NAChRs)的阻断作用机制。短脉冲尼古丁对甲乙胺的内向电流有强烈抑制作用(IC_(50)=0.34微米)，这种作用在洗涤时缓慢可逆。甲乙胺阻断是电压依赖的，并通过结合膜去极化和尼古丁脉冲的方案迅速缓解。去极化或尼古丁脉冲本身不足以引起阻滞缓解。阻滞缓解是短暂的；反应性抑郁以一种使用依赖的方式恢复。如果nAChRs不被尼古丁激活或在膜电位为正的情况下被激活，暴露于甲戊胺不能阻断nAChRs。这些数据表明，无论是静息状态还是去极化水平，甲氨基甲胺都不能与受体相互作用。其他烟碱拮抗剂，如二氢-β-乙酸乙二胺或管库拉林，不分享甲乙胺的这一作用，尽管Proadifen部分地模仿了它。甲基胺被认为可以穿透并阻断开放的nAChRs，nAChRs随后关闭并捕获该拮抗剂。计算机模拟表明，甲氨基甲胺的阻断作用机制可以用假设1)甲氨基甲胺阻断的受体具有慢得多的电压依赖的异构化速率，2)甲氨基甲胺解离的速率常数大且电压依赖性差来描述。因此，通道重新开放加上去极化，允许甲氨基甲胺逃逸和阻断解除。因此，在甲基胺的存在下，nAChRs获得了作为符合探测器的新特性，以检测伴随着膜电位和受体占有率的变化。
The mechanism responsible for the blocking action of mecamylamine on neuronal nicotinic acetylcholine receptors (nAChRs) was studied on rat isolated chromaffin cells recorded under whole-cell patch clamp. Mecamylamine strongly depressed (IC50 = 0.34 mu M) inward currents elicited by short pulses of nicotine, an effect slowly reversible on wash. The mecamylamine block was voltage-dependent and promptly relieved by a protocol combining membrane depolarization with a nicotine pulse. Either depolarization or nicotine pulses were insufficient per se to elicit block relief. Block relief was transient; response depression returned in a use-dependent manner. Exposure to mecamylamine failed to block nAChRs if they were not activated by nicotine or if they were activated at positive membrane potentials. These data suggest that mecamylamine could not interact with receptors either at rest or at depolarized level. Other nicotinic antagonists like dihydro-beta-erythroidine or tubocurarine did not share this action of mecamylamine although proadifen partly mimicked it. Mecamylamine is suggested to penetrate and block open nAChRs that would subsequently close and trap this antagonist. Computer modeling indicated that the mechanism of mecamylamine blocking action could be described by assuming that 1) mecamylamine-blocked receptors possessed a much slower, voltage-dependent isomerization rate, 2) the rate constant for mecamylamine unbinding was large and poorly voltage dependent. Hence, channel reopening plus depolarization allowed mecamylamine escape and block relief. In the presence of mecamylamine, therefore, nAChRs acquire the new property of operating as coincidence detectors for concomitant changes in membrane potential and receptor occupancy.