Laver D R
Division of Neuroscience, John Curtin School of Medical Research, Australian National University, A.C.T.
Biophys J. 1994 Feb;66(2 Pt 1):355-9. doi: 10.1016/s0006-3495(94)80784-2.
Alamethicin and its analogs from cation selective, multi-conductance channels in lipid bilayers. The conductance levels have been thought to be due to a barrel-stave structure where conducting pores (barrels) are formed by the self-assembly of a variable number of alpha-helical rods (staves). The conductance transitions were then interpreted as the addition or deletion of peptide monomers from the pore-forming complex (Sansom, M.S. 1991. Prog. Biophys. Mol. Biol. 55:139-235). Initially, pore conductances were calculated from that expected of right circular cylinders of "bulk" electrolyte. More recent theories also included the access resistance of the electrolyte outside the pore. However, they all consistently overestimated the observed conductances. The reason for the discrepancy is presented here. Previous theories ignored the effects of ion concentration gradients near the pore. Hence, they only held in the limit of small bilayer potentials (< 25 mV) and so would overestimate measurements that typically used much larger potentials (> 100 mV). This theoretical flaw is corrected by using Läuger's theory of diffusion-limited ion flow (Läuger, P. 1976. Biochim. Biophys. Acta. 455:493-509). Thus, including the effects of ion concentration gradients results in a considerable improvement in predicting pore conductances. It is found that: 1) the effects of ion concentration gradients must be included in the barrel-stave model for it to apply to the available data; 2) previously published explanations for the discrepancy between the model and the data, namely the "distorted bundle" and the "head-to-tail aggregate" hypotheses are not necessary (reviewed by Sansom, 1991).
阿拉米辛及其类似物可形成脂质双分子层中的阳离子选择性、多电导通道。人们认为电导水平归因于桶板结构，其中导电孔（桶）由可变数量的α-螺旋杆（板条）自组装形成。然后，电导转变被解释为成孔复合物中肽单体的添加或缺失（桑瑟姆，M.S. 1991。生物物理与分子生物学进展。55:139 - 235）。最初，孔电导是根据“本体”电解质的直圆柱预期值计算的。最近的理论还包括孔外电解质的接入电阻。然而，它们都一致高估了观测到的电导。此处给出了差异的原因。先前的理论忽略了孔附近离子浓度梯度的影响。因此，它们仅在小双分子层电位（< 25 mV）的极限情况下成立，所以会高估通常使用大得多的电位（> 100 mV）的测量值。通过使用劳格的扩散限制离子流理论（劳格，P. 1976。生物化学与生物物理学报。455:493 - 509）纠正了这一理论缺陷。因此，考虑离子浓度梯度的影响在预测孔电导方面有相当大的改进。发现：1）离子浓度梯度的影响必须包含在桶板模型中，使其适用于现有数据；2）先前发表的关于模型与数据差异的解释，即“扭曲束”和“头对头聚集体”假设并非必要（桑瑟姆综述，1991）。
