The permeability of the endplate channel to organic cations in frog muscle.
The permeability of the endplate channel to organic cations in frog muscle.
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DOI：
10.1085/jgp.75.5.469
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发表时间：
1980-05
影响因子：
3.8
通讯作者：
Hille, B
中科院分区：
文献类型：
--
作者：
Dwyer, T M;Adams, D J;Hille, B
端板通道对多种有机阳离子的相对渗透率由反电位判据确定。采用凡士林间隙、电压箝位法，研究了乙酰胆碱离子吸附性“泡”引起的终板电流。当洗浴介质的NaCl被有机阳离子盐取代时，测量了反转电位的变化，并根据Goldman-Hodgkin-Katz方程计算了相对于Na+离子的渗透率比。40个小的单价有机阳离子的渗透率大于0.1。NH4+、羟胺、联氨、甲胺、胍和胍的几个亲缘化合物的渗透率在1.3—2.0之间。然而，即使是咪唑、胆碱、三（羟甲基）氨基甲烷、三乙胺和甘氨酸甲基lester等阳离子也能明显渗透，渗透比为0.13—0.95。此外，还研究了四种含两个带电荷氮基团的化合物。渗透离子的分子模型表明，开放孔的最小横截面必须至少与正方形一样大，6.5 a x 6.5 a。在决定终板通道的离子选择性时，特定的化学因素似乎不如通道或摩擦重要。
The relative permeability of endplate channels to many organic cations was determined by reversal-potential criteria. Endplate currents induced by iontophoretic "puffs" of acetylcholine were studied by a Vaseline gap, voltage clamp method in cut muscle fibers. Reversal potential changes were measured as the NaCl of the bathing medium was replaced by salts of organic cations, and permeability ratios relative to Na+ ions were calculated from the Goldman-Hodgkin-Katz equation. 40 small monovalent organic cations had permeability ratios larger than 0.1. The most permeant including NH4+, hydroxylamine, hydrazine, methylamine, guanidine, and several relatives of guanidine had permeability ratios in the range 1.3--2.0. However, even cations such as imidazole, choline, tris(hydroxymethyl)aminomethane, triethylamine, and glycine methylester were appreciably permeant with permeability ratios of 0.13--0.95. Four compounds with two charged nitrogen groups were also permeant. Molecular models of the permeant ions suggest that the smallest cross-section of the open pore must be at least as large as a square, 6.5 A x 6.5 A. Specific chemical factors seem to be less important than access or friction in determining the ionic selectivity of the endplate channel.