BATRACHOTOXIN-MODIFIED SODIUM-CHANNELS IN PLANAR LIPID BILAYERS - ION PERMEATION AND BLOCK
BATRACHOTOXIN-MODIFIED SODIUM-CHANNELS IN PLANAR LIPID BILAYERS - ION PERMEATION AND BLOCK
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DOI：
10.1085/jgp.89.6.841
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发表时间：
1987-06-01
影响因子：
3.8
通讯作者：
ANDERSEN, OS
中科院分区：
文献类型：
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作者：
GREEN, WN;WEISS, LB;ANDERSEN, OS
将犬前脑的Batrachotoxin修饰的电压依赖性钠通道纳入平面脂质双层。单通道电导进行了研究[Na+]范围为0.02和3.5 M。通常，单通道电流表现出简单的两态行为，在闭合和完全打开状态之间转换。观察到另外两种电导状态：亚电导状态，通常在[NaCl] ≥0.5 M和闪烁状态，通常在[NaCl] ≤。0.5 M.当[NaCl]降低到0.5M以下时，闪烁状态变得更加频繁。K+/Na+渗透率比为约。0.16在0.5和2.5 M盐中，独立于Na+摩尔分数，这表明在通道中渗透离子之间没有相互作用。不渗透性和渗透性阻断离子（四乙基铵，Ca++，Zn++，和K+）有不同的效果时，加入到细胞外和细胞内的解决方案，这表明该通道是不对称的，并有至少两个阳离子结合位点。电导率与[Na+]的关系在高浓度下饱和，但不能用朗缪尔等温线描述，因为在低[NaCl]下的电导率高于从在[NaCl] ≥ 2.0时的数据预测的电导率。1.0 M.在低[NaCl]（≤0.1 M）时，通过添加不渗透的一价和二价阳离子来增加离子强度降低了电导，就好像通道入口处的负静电势的大小降低了一样。对于携带净负电荷的双层和不携带净电荷的双层中的通道，电导相当。总之，这些结果导致这样的结论，即通道入口附近的通道蛋白上的负电荷增加了电导，而脂质表面电荷不太重要。
Batrachotoxin-modified, voltage-dependent sodium channels from canine forebrain were incorporated into planar lipid bilayers. Single-channel conductances were studied for [Na+] ranging between 0.02 and 3.5 M. Typically, the single-channel currents exhibited a simple two-state behavior, with transitions between closed and fully open states. Two other conductance states were observed: a subconductance state, usually seen at [NaCl] .gtoreq. 0.5 M, and a flickery state, usually seen at [NaCl] .ltoreq. 0.5 M. The flickery state became more frequent as [NaCl] was decreased below 0.5 M. The K+/Na+permeability ratio was .apprx. 0.16 in 0.5 and 2.5 M salt, independent of the Na+ mole fraction, which indicates that there are no interactions among permeant ions in the channels. Impermeant and permeant blocking ions (tetraethylammonium, Ca++, Zn++, and K+) have different effects when added to the extracellular and intracellular solutions, which indicates that the channel is asymmetrical and has at least two cation-binding sites. The conductance vs. [Na+] relation saturated at high concentrations, but could not be described by a Langmuir isotherm, as the conductance at low [NaCl] is higher than predicted from the data at [NaCl] .gtoreq. 1.0 M. At low [NaCl] (.ltoreq. 0.1 M), increasing the ionic strength by additions of impermeant monovalent and divalent cations reduced the conductance, as if the magnitude of negative electrostatic potentials at the channel entrances were reduced. The conductances were comparable for channels in bilayers that carry a net negative charge and bilayers that carry no net charge. Together, these results lead to the conclusion that negative charges on the channel protein near the channel entrances increase the conductance, while lipid surface charges are less important.