Tyerman S D, Terry B R, Findlay G P
School of Biological Sciences, Flinders University of South Australia, Bedford Park.
Biophys J. 1992 Mar;61(3):736-49. doi: 10.1016/S0006-3495(92)81878-7.
The large conductance K+ channel in the tonoplast of Chara corallina has subconductance states (substates). We describe a method that detects substates by monitoring the time derivative of channel current. Substates near to the full conductance tend to have long durations and high probabilities, while those of smaller amplitude occur with less probability and short duration. The substate pattern is similar in cell-attached, inside-out and outside-out patches over a range of temperatures. The pattern changes at high Ca2+ concentration (10 mol m-3) on the cytoplasmic face of inside-out patches. One substate at approximately 50% of the full conductance is characterized by a high frequency of transitions from the full conductance level. This midstate conductance is not a constant proportion of the full conductance but changes as a function of membrane potential difference (p.d.) showing strong inward rectification. We suggest that the channel is a single pore that can change conformation and/or charge profile to give different conductances. The mean durations of the full conductance level and the midstate decrease as the membrane p.d. becomes more negative. Programs for analysis of channel kinetics based on an half-amplitude detection criterion are shown to be unsuitable for analysis of the K+ channel.
轮藻液泡膜上的大电导钾通道具有亚电导状态（亚态）。我们描述了一种通过监测通道电流的时间导数来检测亚态的方法。接近全电导的亚态往往持续时间长且概率高，而幅度较小的亚态出现概率低且持续时间短。在一系列温度下，细胞贴附式、内面向外式和外面向外式膜片的亚态模式相似。在内面向外式膜片细胞质面的高Ca2+浓度（10 mol m-3）下，模式会发生变化。约为全电导50%的一个亚态的特征是从全电导水平转变的频率很高。这种中间态电导不是全电导的固定比例，而是随膜电位差（p.d.）变化，表现出强烈的内向整流。我们认为该通道是一个单孔道，可改变构象和/或电荷分布以产生不同的电导。随着膜p.d.变得更负，全电导水平和中间态的平均持续时间会缩短。基于半幅度检测标准的通道动力学分析程序被证明不适用于钾通道的分析。
