McCleskey E W, Almers W
Proc Natl Acad Sci U S A. 1985 Oct;82(20):7149-53. doi: 10.1073/pnas.82.20.7149.
The permeability of Ca channels to various foreign cations has been investigated in the absence of external Ca2+. All physiological metal cations are clearly permeant, including Mg2+. The large organic cation n-butylamine+ is sparingly permeant or impermeant, but its larger derivative 1,4-diaminobutane2+ is highly permeant. Among the cations of the methylated ammonium series, permeability diminishes in a graded fashion as ion size increases. Tetramethylammonium, the largest cation found to be permeant, has a diameter of about 6 A; hence, the aqueous pore of the Ca channel at its narrowest point can be no smaller. That the pore is so large strengthens our view that, under physiologic conditions, the high selectivity of Ca channels is due to selective binding of Ca2+ rather than to rejection of other cations by, for example, a sieving mechanism.
在无细胞外Ca2+的情况下，研究了Ca通道对各种外来阳离子的通透性。所有生理性金属阳离子显然都是可通透的，包括Mg2+。大的有机阳离子正丁胺+通透性较低或不通透，但其较大的衍生物1,4 - 二氨基丁烷2+则具有高度通透性。在甲基化铵系列阳离子中，随着离子尺寸增大，通透性呈梯度降低。四甲基铵是已发现的可通透的最大阳离子，直径约为6 Å；因此，Ca通道最窄处的水相孔道不可能更小。孔道如此之大，强化了我们的观点，即在生理条件下，Ca通道的高选择性是由于Ca2+的选择性结合，而非例如通过筛分机制排斥其他阳离子。
