Bean R C, Shepherd W C, Chan H, Eichner J
J Gen Physiol. 1969 Jun;53(6):741-57. doi: 10.1085/jgp.53.6.741.
Discrete fluctuations in conductance of lipid bilayer membranes may be observed during the initial stages of membrane interaction with EIM ("excitability inducing material"), during destruction of the EIM conductance by proteolysis, and during the potential-dependent transitions between low and high conductance states in the "excitable" membranes. The discrete conductance steps observed during the initial reaction of EIM with the lipid membranes are remarkably uniform, even in membranes of widely varying lipid composition. They range only from 2 to 6 x 10(-10) ohm(-1) and average 4 x 10(-10) ohm(-1). Steps found during destruction of the EIM conductance by proteolysis are somewhat smaller. The transition between high conductance and low conductance states may involve steps as small as 0.5 x 10(-10) ohm(-1). These phenomena are consistent with the formation of a stable protein bridge across the lipid membrane to provide a polar channel for the transport of cations. T6he uniform conductance fluctuations observed during the formation of these macromolecular channels may indicate that the ions in a conductive channel, in its open state, are largely protected from the influence of the polar groups of the membrane lipids. Potential-dependent changes in conductance may be due to configurational or positional changes in the protein channel. Differences in lipid-lipid and lipid-macromolecule interactions may account for the variations in switching kinetics in various membrane systems.
在脂质双分子层膜与EIM（“兴奋性诱导物质”）相互作用的初始阶段、EIM电导因蛋白水解而被破坏的过程中，以及在“可兴奋”膜中低电导状态和高电导状态之间的电位依赖性转变过程中，均可观察到脂质双分子层膜电导的离散波动。即使在脂质组成差异很大的膜中，在EIM与脂质膜的初始反应过程中观察到的离散电导步长也非常均匀。它们仅在2至6×10⁻¹⁰欧姆⁻¹之间，平均为4×10⁻¹⁰欧姆⁻¹。在蛋白水解破坏EIM电导的过程中发现的步长稍小一些。高电导状态和低电导状态之间的转变可能涉及小至0.5×10⁻¹⁰欧姆⁻¹的步长。这些现象与跨脂质膜形成稳定的蛋白质桥以提供阳离子运输的极性通道相一致。在这些大分子通道形成过程中观察到的均匀电导波动可能表明处于开放状态的导电通道中的离子在很大程度上免受膜脂质极性基团的影响。电位依赖性电导变化可能是由于蛋白质通道的构象或位置变化引起的。脂质-脂质和脂质-大分子相互作用的差异可能解释了各种膜系统中开关动力学的变化。
