Dwyer T M, Adams D J, Hille B
J Gen Physiol. 1980 May;75(5):469-92. doi: 10.1085/jgp.75.5.469.
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.
通过反转电位标准确定终板通道对许多有机阳离子的相对通透性。采用凡士林间隙电压钳法，在切断的肌纤维中研究了离子电泳“微喷射”乙酰胆碱诱导的终板电流。当用有机阳离子盐替代浴液中的氯化钠时，测量反转电位的变化，并根据戈德曼-霍奇金- Katz方程计算相对于钠离子的通透率。40种小的单价有机阳离子的通透率大于0.1。通透性最强的包括铵离子、羟胺、肼、甲胺、胍以及几种胍的衍生物，其通透率在1.3 - 2.0范围内。然而，即使是咪唑、胆碱、三（羟甲基）氨基甲烷、三乙胺和甘氨酸甲酯等阳离子也有明显的通透性，通透率为0.13 - 0.95。四种带有两个带电荷氮基团的化合物也具有通透性。通透离子的分子模型表明开放孔的最小横截面积必须至少与一个6.5埃×6.5埃的正方形一样大。在决定终板通道的离子选择性方面，特定的化学因素似乎不如通道入口或摩擦力重要。
