Chalfant M L, O'Brien T G, Civan M M
Lankenau Medical Research Center, Wynnewood 19096, USA.
Am J Physiol. 1996 Apr;270(4 Pt 1):C998-1010. doi: 10.1152/ajpcell.1996.270.4.C998.
Amiloride-sensitive whole cell currents have been reported in M-1 mouse cortical collecting duct cells (Korbmacher et al., J. Gen. Physiol. 102: 761-793, 1993). We have confirmed that amiloride inhibits the whole cell currents but not necessarily the measured whole cell currents. Anomalous responses were eliminated by removing external Na+ and/or introducing paraepithelial shunts. The amiloride-sensitive whole cell currents displayed Goldman rectification. The ionic selectivity sequence of the amiloride-sensitive conductance was Li+ > Na+ >> K+. Growth of M-1 cells on permeable supports increased the amiloride-sensitive whole cell permeability, compared with cells grown on plastic. Single amiloride-sensitive channels were observed, which conformed to the highly selective low-conductance amiloride-sensitive class [Na(5)] of epithelial Na+ channels. Hypotonic pretreatment markedly slowed run-down of channel activity. The gating of the M-1 Na+ channel in excised patches was complex. Open- and closed-state dwell-time distributions from patches that display one operative channel were best described with two or more exponential terms each. We conclude that 1) study of M-1 whole cell Na+ currents is facilitated by reducing the transepithelial potential to zero, 2) these M-1 currents reflect the operation of Na(5) channels, and 3) the Na+ channels display complex kinetics, involving > or = 2 open and > or = 2 closed states.
据报道，在M-1小鼠皮质集合管细胞中存在氨氯地平敏感的全细胞电流（Korbmacher等人，《普通生理学杂志》102: 761 - 793, 1993）。我们已证实氨氯地平抑制全细胞电流，但不一定是所测量的全细胞电流。通过去除细胞外Na⁺和/或引入上皮旁通路可消除异常反应。氨氯地平敏感的全细胞电流表现出戈德曼整流。氨氯地平敏感电导的离子选择性顺序为Li⁺ > Na⁺ >> K⁺。与在塑料上生长的细胞相比，M-1细胞在可渗透支持物上生长增加了氨氯地平敏感的全细胞通透性。观察到单个氨氯地平敏感通道，其符合上皮Na⁺通道的高选择性低电导氨氯地平敏感类别[Na(5)]。低渗预处理显著减缓了通道活性的衰减。切除的膜片中M-1 Na⁺通道的门控很复杂。对于显示一个有效通道的膜片，开放和关闭状态的驻留时间分布最好用两个或更多指数项来描述。我们得出结论：1）通过将跨上皮电位降至零有助于研究M-1全细胞Na⁺电流；2）这些M-1电流反映了Na(5)通道的运作；3）Na⁺通道表现出复杂的动力学，涉及≥2个开放状态和≥2个关闭状态。
