Wills N K, Millinoff L P
Department of Physiology and Biophysics, University of Texas Medical Br., Galveston 77550-2781.
Pflugers Arch. 1990 Jul;416(5):481-92. doi: 10.1007/BF00382680.
Electrical techniques were used to determine the Na:K selectivity of the amiloride-sensitive pathway and to characterize cellular and paracellular properties of A6 epithelium. Under control conditions, the mean transepithelial voltage (VT) was -57 +/- 5 mV, the short-circuit current (Isc) averaged 23 +/- 2 microA/cm2 and the transepithelial resistance (RT) was 2.8 +/- 0.3 k omega cm2 (n = 13). VT and Isc were larger than reported in previous studies and were increased by aldosterone. The conductance of the amiloride-sensitive pathway (Gamil) was assessed before and after replacement of Na+ in the mucosal bath by K+, using two independent measurements: (1) the slope conductance (GT), determined from current-voltage (I-V) relationships for control and amiloride-treated tissues and (2) the maximum amiloride-sensitive conductance (Gmax) calculated from the amiloride dose-response relationship. The ratio of Gamil in mucosal Na+ solutions to Gamil for mucosal K+ solutions was 22 +/- 6 for GT measurements and 15 +/- 2 for Gmax data. Serosal ion replacements in tissues treated with mucosal nystatin indicated a potassium conductance in the basolateral membrane. Equivalent circuit analyses of nystatin and amiloride data were used to resolve the cellular (Ec) and paracellular (Rj) resistances (approximately 5 k omega cm2 and 8-9 k omega cm2, respectively). Analysis of I-V relationships for tissues depolarized with serosal K+ solutions revealed that the amiloride-sensitive pathway could be described as a Na+ conductance with a permeability coefficient (PNa) = 1.5 +/- 0.2 x 10(-6) cm/s and the intracellular Na+ concentration (Nai) = 5 +/- 1 mM (n = 5), similar to values from other tight epithelia. We conclude that A6 epithelia are capable of expressing large amiloride-sensitive currents which are highly Na+ selective.
采用电学技术来确定氨氯地平敏感途径的钠钾选择性，并表征A6上皮细胞的细胞和细胞旁特性。在对照条件下，平均跨上皮电压（VT）为-57±5 mV，短路电流（Isc）平均为23±2 μA/cm²，跨上皮电阻（RT）为2.8±0.3 kΩ·cm²（n = 13）。VT和Isc比先前研究报道的要大，且会因醛固酮而增加。通过用钾替代黏膜浴中的钠前后，使用两种独立测量方法评估氨氯地平敏感途径的电导（Gamil）：（1）斜率电导（GT），由对照和氨氯地平处理组织的电流-电压（I-V）关系确定；（2）根据氨氯地平剂量-反应关系计算的最大氨氯地平敏感电导（Gmax）。对于GT测量，黏膜钠溶液中的Gamil与黏膜钾溶液中的Gamil之比为22±6，对于Gmax数据为15±2。在用黏膜制霉菌素处理的组织中进行浆膜离子替代表明，基底外侧膜存在钾电导。对制霉菌素和氨氯地平数据进行等效电路分析，以解析细胞电阻（Ec）和细胞旁电阻（Rj）（分别约为5 kΩ·cm²和8 - 9 kΩ·cm²）。对用浆膜钾溶液去极化的组织的I-V关系分析表明，氨氯地平敏感途径可描述为钠电导，其通透系数（PNa） = 1.5±0.2×10⁻⁶ cm/s，细胞内钠浓度（Nai） = 5±1 mM（n = 5），与其他紧密上皮细胞的值相似。我们得出结论，A6上皮细胞能够表达大的氨氯地平敏感电流，且该电流具有高度的钠选择性。
