Nelson M T
J Gen Physiol. 1986 Feb;87(2):201-22. doi: 10.1085/jgp.87.2.201.
Voltage-dependent calcium channels from a rat brain membrane preparation ("synaptosomes") were incorporated into planar lipid bilayers. The effects of calcium, barium, strontium, manganese, and cadmium ions on the amplitudes and kinetics of single channel currents were examined. The order of single channel conductances was gBa greater than gSr greater than gMn, which was the inverse of the order of the mean channel open times: TMn greater than TCa = TSr greater than TBa. In contrast, the identity of the charge carrier had little or no effect on the mean closed times of the channel. Manganese, in the absence of other permeant ions, can pass through single channels (gMn = 4 pS). However, when added to a solution that contained another type of permeant divalent cation, manganese reduced the single channel current in a voltage-dependent manner. Cadmium, a potent blocker of macroscopic "ensemble" calcium currents in many preparations, reduced the current through an open channel in a manner consistent with Cd ions both not being measurably permeant and interacting with a single site. The permeant ions competed with cadmium for this site with the following order: Mn greater than Sr = Ca greater than Ba. These results are consistent with the existence of no less than one divalent cation binding site in the channel that regulates ion permeation.
将来自大鼠脑膜制剂（“突触体”）的电压依赖性钙通道整合到平面脂质双分子层中。研究了钙、钡、锶、锰和镉离子对单通道电流幅度和动力学的影响。单通道电导的顺序为gBa＞gSr＞gMn，这与平均通道开放时间的顺序相反：TMn＞TCa = TSr＞TBa。相比之下，电荷载体的性质对通道的平均关闭时间几乎没有影响。在没有其他渗透离子的情况下，锰可以通过单通道（gMn = 4 pS）。然而，当添加到含有另一种渗透二价阳离子的溶液中时，锰以电压依赖性方式降低单通道电流。镉是许多制剂中宏观“整体”钙电流的有效阻滞剂，它以与Cd离子既不可测量地渗透又与单个位点相互作用一致的方式降低通过开放通道的电流。渗透离子与镉竞争该位点的顺序如下：Mn＞Sr = Ca＞Ba。这些结果与通道中至少存在一个调节离子渗透的二价阳离子结合位点一致。
