Horisberger J D, Giebisch G
Department of Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
J Membr Biol. 1988 Nov;105(3):257-63. doi: 10.1007/BF01871002.
The basolateral potassium conductance of cells of most epithelial cells plays an important role in the transcellular sodium transport inasmuch as the large negative equilibrium potential of potassium across this membrane contributes to the electrical driving force for Na+ across the apical membrane. In the present study, we have attempted to establish the I-V curve of the basolateral membrane of the Amphiuma collecting tubule, a membrane shown to be K+ selective. Transepithelial I-V curves were obtained in short, isolated perfused collecting tubule segments. The "shunt" conductance was determined using amiloride to block the apical membrane Na+ conductance. In symmetrical solutions, the "shunt" I-V curve was linear (conductance: 2.2 +/- 0.3 mS.cm-2). Transcellular current was calculated by subtracting the "shunt" current from the transepithelial current in the absence of amiloride. Using intracellular microelectrodes, it was then possible to measure the basolateral membrane potential simultaneously with the transcellular current. The basolateral conductance was found to be voltage dependent, being activated by hyperpolarization: conductance values at -30 and -80 mV were 3.6 +/- 1.0 and 6.6 +/- 1.0 mS.cm-2, respectively. Basolateral I-V curves were thus clearly different from that predicted by the "constant field" model. These results indicate that the K+-selective basolateral conductance of an amphibian collecting tubule shows inward ("anomalous") rectification. Considering the electrogenic nature basolateral Na-K-pump, this may account for coupling between pump-generated potential and basolateral K+ conductance.
大多数上皮细胞的基底外侧钾电导在跨细胞钠转运中起重要作用，因为钾跨此膜的大的负平衡电位有助于钠跨顶端膜的电驱动力。在本研究中，我们试图建立蚓螈集合管基底外侧膜的电流-电压（I-V）曲线，该膜显示对钾具有选择性。在短的、分离的灌注集合管段中获得跨上皮I-V曲线。使用氨氯吡咪阻断顶端膜钠电导来测定“旁路”电导。在对称溶液中，“旁路”I-V曲线是线性的（电导：2.2±0.3 mS·cm-2）。在不存在氨氯吡咪的情况下，通过从跨上皮电流中减去“旁路”电流来计算跨细胞电流。然后使用细胞内微电极能够同时测量基底外侧膜电位和跨细胞电流。发现基底外侧电导是电压依赖性的，由超极化激活：在-30和-80 mV时的电导值分别为3.6±1.0和6.6±1.0 mS·cm-2。因此，基底外侧I-V曲线明显不同于“恒定场”模型所预测的曲线。这些结果表明，两栖动物集合管的钾选择性基底外侧电导表现出内向（“反常”）整流。考虑到基底外侧钠钾泵的生电性质，这可能解释了泵产生的电位与基底外侧钾电导之间的耦合。
