Neuroscience & Physiology, SUNY Upstate Medical University, Syracuse, NY, USA.
Channels (Austin). 2013 May-Jun;7(3):182-93. doi: 10.4161/chan.24455. Epub 2013 Apr 1.
Local anesthetics and related drugs block ionic currents of Na (+) , K (+) and Ca ( 2+) conducted across the cell membrane by voltage-dependent ion channels. Many of these drugs bind in the permeation pathway, occlude the pore and stop ion movement. However channel-blocking drugs have also been associated with decreased membrane stability of certain tetrameric K (+) channels, similar to the destabilization of channel function observed at low extracellular K (+) concentration. Such drug-dependent stability may result from electrostatic repulsion of K (+) from the selectivity filter by a cationic drug molecule bound in the central cavity of the channel. In this study we used the pore domain of the KcsA K (+) channel protein to test this hypothesis experimentally with a biochemical assay of tetramer stability and theoretically by computational simulation of local anesthetic docking to the central cavity. We find that two common local anesthetics, lidocaine and tetracaine, promote thermal dissociation of the KcsA tetramer in a K (+) -dependent fashion. Docking simulations of these drugs with open, open-inactivated and closed crystal structures of KcsA yield many energetically favorable drug-channel complexes characterized by nonbonded attraction to pore-lining residues and electrostatic repulsion of K (+) . The results suggest that binding of cationic drugs to the inner cavity can reduce tetramer stability of K (+) channels.
局部麻醉剂和相关药物通过电压门控离子通道阻断跨细胞膜的 Na(+)、K(+)和 Ca(2+)离子电流。这些药物中的许多结合在渗透途径中，阻塞孔并阻止离子运动。然而，通道阻断药物也与某些四聚体 K(+)通道的膜稳定性降低有关，类似于在低细胞外 K(+)浓度下观察到的通道功能不稳定。这种药物依赖性稳定性可能是由于结合在通道中心腔中的阳离子药物分子排斥 K(+)从选择性过滤器中产生的静电排斥。在这项研究中，我们使用 KcsA K(+)通道蛋白的孔域，通过四聚体稳定性的生化测定实验和局部麻醉剂对接中央腔的计算模拟理论来测试这一假设。我们发现两种常见的局部麻醉剂，利多卡因和丁卡因，以 K(+)依赖性的方式促进 KcsA 四聚体的热解离。这些药物与 KcsA 的开放、开放失活和关闭晶体结构的对接模拟产生了许多能量有利的药物通道复合物，其特征是与孔衬里残基的非键吸引力和 K(+)的静电排斥。结果表明，阳离子药物与内腔的结合可以降低 K(+)通道的四聚体稳定性。
