Conductance and gating of epithelial Na channels from rat cortical collecting tubule. Effects of luminal Na and Li.
Conductance and gating of epithelial Na channels from rat cortical collecting tubule. Effects of luminal Na and Li.
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DOI：
10.1085/jgp.92.1.121
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发表时间：
1988-07
期刊：
影响因子：
--
通讯作者：
Frindt G
中科院分区：
文献类型：
--
作者：
Palmer LG;Frindt G
本文研究了在不同浓度的Na和Li渗透下，大鼠皮质集合管（CCT）顶膜单个Na通道的行为。打开小管以暴露其管腔表面，并浸泡在葡萄糖酸钾培养基中，以最大限度地减少细胞膜电位和细胞内Na浓度的小管间差异。膜片钳技术用于解析通过各个通道的电流。膜片钳移液器充满含有不同浓度NaCl或LiCl的溶液。在一系列实验中，改变浓度而不进行替换。在另一系列中，离子强度和Cl浓度通过用N-甲基-D-葡糖胺（NMDG）部分取代Li来保持恒定。在细胞贴附的贴片中，单通道电导（g）和单通道电流（i）都饱和，作为移液管中Na或Li活性的函数。在没有NMDG的情况下，通过Michaelis-Menten动力学很好地描述了i的饱和，其中Na的表观Km为约20 mM活性，Li的表观Km为约50 mM活性。两种离子的Km均与电压无关。用NMDG取代Li后，Li在通道中的表观Km值增加。通道开放的概率（Po）的值因贴片而异，但没有表现出移液管离子活性对Po的影响。观察到PO对膜电压的弱依赖性，超极化使PO平均增加2.3%/mV。
The behavior of individual Na channels in the apical membrane of the rat cortical collecting tubule (CCT) was studied at different concentrations of the permeant ions Na and Li. Tubules were opened to expose their luminal surfaces and bathed in K-gluconate medium to minimize tubule-to-tubule variation in cell membrane potential and intracellular Na concentration. The patch-clamp technique was used to resolve currents through individual channels. The patch-clamp pipette was filled with solutions containing variable concentrations of either NaCl or LiCl. In one series of experiments, the concentrations were changed without substitutions. In another series, the ionic strength and Cl concentration were maintained constant by partial substitution of Li with N-methyl-D-glucamine (NMDG). In cell-attached patches, both the single-channel conductance (g) and the single-channel current (i) saturated as functions of the Na or Li activity in the pipette. Without NMDG, the saturation of i was well described by Michaelis-Menten kinetics with an apparent Km of approximately 20 mM activity for Na and approximately 50 mM activity for Li. Km was independent of voltage for both ions. With substitution for Li by NMDG, the apparent Km value for Li transport through the channels increased. The values of the probability of a channel's being open (Po) varied from patch to patch, but no effect of pipette ion activity on Po could be demonstrated. A weak dependence of Po on membrane voltage was observed, with hyperpolarization increasing Po by an average of 2.3%/mV.