Hanke W, Cook N J, Kaupp U B
Fachbereich Biologie/Chemie, Abteilung Biophysik, Universität Osnabrück, Federal Republic of Germany.
Proc Natl Acad Sci U S A. 1988 Jan;85(1):94-8. doi: 10.1073/pnas.85.1.94.
The cGMP-dependent channel protein has been purified from bovine rod photoreceptor membranes and incorporated into planar lipid membranes. At low divalent cation concentrations, cGMP stimulated single-channel current fluctuations. The probability Po of the channel being open strongly depended on the cGMP concentration (EC50 = 31 microM; Hill coefficient, n = 2.3); whereas the single-channel conductance (lambda = 26 pS) was independent of the agonist concentration. The agonist-stimulated increase in the probability of an open channel was largely due to shorter closed times and, to a lesser extent, due to the channel staying open for a longer time. The current-voltage relationship of the single open channel deviated from ohmic behavior, and the open probability decreased at more negative membrane potentials. The rectification of the macroscopic cGMP-induced current in artificial bilayers that contained many channel copies can be accounted for by the voltage dependence of channel gating together with the nonlinearity of the current-voltage curve of an open channel. Current fluctuations exhibited a variety of sublevels, indicating that the channel may exist in more than one conductive state.
环磷酸鸟苷（cGMP）依赖性通道蛋白已从牛视杆光感受器膜中纯化出来，并整合到平面脂质膜中。在低二价阳离子浓度下，cGMP刺激单通道电流波动。通道开放的概率Po强烈依赖于cGMP浓度（半数有效浓度EC50 = 31微摩尔；希尔系数n = 2.3）；而单通道电导（λ = 26皮安）与激动剂浓度无关。激动剂刺激导致通道开放概率增加，主要是由于关闭时间缩短，在较小程度上是由于通道开放时间延长。单个开放通道的电流-电压关系偏离欧姆行为，且在更负的膜电位下开放概率降低。在含有许多通道拷贝的人工双层膜中，宏观cGMP诱导电流的整流可由通道门控的电压依赖性以及开放通道电流-电压曲线的非线性来解释。电流波动表现出多种亚水平，表明通道可能存在不止一种导电状态。
