Morier N, Sauvé R
Département de physiologie, Université de Montréal, Québec, Canada.
Biophys J. 1994 Aug;67(2):590-602. doi: 10.1016/S0006-3495(94)80519-3.
The presence of anionic channels in stripped rough endoplasmic reticulum membranes isolated from rat hepatocytes was investigated by fusing microsomes from these membranes to a planar lipid bilayer. Several types of anion-selective channels were observed including a voltage-gated Cl- channel, the activity of which appeared in bursts characterized by transitions among three distinct conductance levels of 0 pS (0 level), 160 pS (O1 level), and 320 pS (O2 level), respectively, in 450 mM (cis) 50 mM (trans) KCl conditions. A chi 2 analysis on current records where interburst silent periods were omitted showed that the relative probability of current levels 0 (baseline), O1, and O2 followed a binomial statistic. However, measurements of the conditional probabilities W(level 0 at tau/level O2 at 0) and W(level O2 at tau/level 0 at 0) provided clear evidence of direct transitions between the current levels 0 and O2 without any detectable transitions to the intermediate level O1. It was concluded on the basis of these results that the observed channel was controlled by at least two distinct gating processes, namely 1) a voltage-dependent activation mechanism in which the entire system behaves as two independent monomeric channels of 160 pS with each channel characterized by a simple Open-Closed kinetic, and 2) a slow voltage-dependent process that accounts for both the appearance of silent periods between bursts of channel activity and the transitions between the current levels 0 and O2. Finally, an analysis of the relative probability for the system to be in levels 0, O1, and O2 showed that our results are more compatible with a model in which all the states resulting from the superposition of the two independent monomeric channels have access at different rates to a common inactivated state than with a model where a simple Open-Closed main gate either occludes or exposes simultaneously two independent 160-pS monomers.
通过将大鼠肝细胞分离的糙面内质网膜中的微粒体与平面脂质双层融合，研究了这些膜中阴离子通道的存在情况。观察到几种类型的阴离子选择性通道，包括电压门控氯离子通道，在450 mM（顺式）50 mM（反式）KCl条件下，其活性以突发形式出现，其特征分别为在三个不同电导水平（0 pS（0水平）、160 pS（O1水平）和320 pS（O2水平））之间转换。对省略突发间期静默期的电流记录进行卡方分析表明，电流水平0（基线）、O1和O2的相对概率遵循二项式统计。然而，对条件概率W（τ时的0水平/0时的O2水平）和W（τ时的O2水平/0时的0水平）的测量提供了明确证据，表明电流水平0和O2之间存在直接转换，而没有任何可检测到的向中间水平O1的转换。基于这些结果得出结论，观察到的通道受至少两种不同的门控过程控制，即1）电压依赖性激活机制，其中整个系统表现为两个独立的160 pS单体通道，每个通道具有简单的开-关动力学特征；2）缓慢的电压依赖性过程，该过程解释了通道活动突发之间静默期的出现以及电流水平0和O2之间的转换。最后，对系统处于0、O1和O2水平的相对概率的分析表明，与简单的开-关主门同时封闭或暴露两个独立的160-pS单体的模型相比，我们的结果更符合这样一种模型，即由两个独立单体通道叠加产生的所有状态以不同速率进入一个共同的失活状态。
