ION-CHANNEL ENTRANCES INFLUENCE PERMEATION - NET CHARGE, SIZE, SHAPE, AND BINDING CONSIDERATIONS
ION-CHANNEL ENTRANCES INFLUENCE PERMEATION - NET CHARGE, SIZE, SHAPE, AND BINDING CONSIDERATIONS
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DOI：
10.1016/s0006-3495(86)83688-8
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发表时间：
1986-03-01
影响因子：
3.4
通讯作者：
DANI, JA
中科院分区：
文献类型：
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作者：
DANI, JA
许多离子通道具有宽的入口，作为过渡区，以更有选择性的狭窄区域的孔。在这里，这些前庭的一些物理特征进行了探讨。它们被认为具有确定的尺寸、漏斗形状和净负电荷。离子大小，离子筛选的带负电荷的残基，阳离子结合，和阻塞的电流进行了分析，以确定如何前庭影响运输。这些属性被耦合到一个Eyring率理论模型的窄长度的孔。结果包括：（a）宽前庭允许孔具有短窄区域。因此，离子遇到较短长度的受限扩散，并且沟道电导可以更大。（B）。前庭中的净负电荷产生的电势吸引阳离子进入孔中。由于该电位随电解质浓度而变化，因此在低电解质浓度下测量的电导大于在高浓度下测量的预期电导。（c）.前庭内的净电荷产生局部电势，该局部电势赋予阳离子与阴离子以及二价与单价的选择性。(d)大的阳离子在屏蔽（减小）净电荷电势方面不太有效，因为它们不能像小的阳离子那样进入孔。因此，在相同的体相浓度下，吸引负电位较大，这导致大的阳离子以较低的浓度饱和孔中的位点。(e)少量的大阳离子或二价阳离子可导致对小的一价阳离子的渗透性质的误解。
Many ion channels have wide entrances that serve as transition zones to the more selective narrow region of the pore. Here some physical features of these vestibules are explored. They are considered to have a defined size, funnel shape, and net-negative charge. Ion size, ionic screening of the negatively charged residues, cation binding, and blockage of current are analyzed to determine how the vestibules influence transport. These properties are coupled to an Eyring rate theory model for the narrow length of the pore. The results include the following: (a) Wide vestibules allow the pore to have a short narrow region. Therefore, ions encounter a shorter length of restricted diffusion, and the channel conductance can be greater. (b). The potential produced by the net-negative charge in the vestibules attracts cations into the pore. Since this potential varies with electrolyte concentration, the conductance measured at low electrolyte concentrations is larger than expected from measurements at high concentration. (c). Net charge inside the vestibules creates a local potential that confers some cation vs. anion, and divalent vs. monovalent selectivity. (d) Large cations are less effective at screening (diminishing) the net-charge potential because they cannot enter the pore as well as small cations. Therefore, at an equivalent bulk concentration the attractive negative potential is larger, which causes large cations to saturate sites in the pore at lower concentrations. (e) Small amounts of large or divalent cations can lead to misinterpretation of the permeation properties of a small monovalent cation.