Frindt Gustavo, Palmer Lawrence G
Dept. of Physiology and Biophysics, Weill Medical College of Cornell Univ., 1300 York Ave., New York, NY 10021, USA.
Am J Physiol Renal Physiol. 2004 Apr;286(4):F669-74. doi: 10.1152/ajprenal.00381.2003. Epub 2003 Dec 2.
Epithelial Na channels were investigated using patch-clamp techniques in connecting tubule (CNT) segments isolated from rat kidney. Cell-attached patches with Li+ in the patch pipette contained channels with conductances for inward currents of 13-16 pS and slow opening and closing kinetics, similar to properties of Na channels in the cortical collecting tubule (CCT). Macroscopic amiloride-sensitive currents (INa) were also observed under whole cell clamp conditions. These currents were undetectable in cells from control rats but were large when the animals were infused with aldosterone (1,380+/-340 pA/cell at a holding potential of -100 mV) or fed a high-K diet (670+/-260 pA/cell) for 1 wk. Under both of these conditions, currents in cells of the CNT were two- to fourfold larger than currents in cells of the CCT of the same animals. In aldosterone-treated animals, currents in cells of the initial collecting tubule (iCT) were intermediate, such that the relative magnitude of INa was as follows: CNT > iCT > CCT. Quantitative analysis of the results suggests that the maximal capacity of the aggregate population of CNTs to reabsorb Na could be as high as 18 micromol/min, or approximately 10% of the filtered load of Na. This capacity is approximately 10 times higher than that of the CCT.
采用膜片钳技术，对从大鼠肾脏分离出的连接小管（CNT）节段中的上皮钠通道进行了研究。膜片钳微管中含有Li⁺的细胞贴附式膜片所记录到的通道，其内向电流的电导为13 - 16 pS，开闭动力学缓慢，类似于皮质集合管（CCT）中钠通道的特性。在全细胞钳制条件下也观察到了宏观的氨氯地平敏感电流（INa）。这些电流在对照大鼠的细胞中未检测到，但当动物接受醛固酮灌注（在 - 100 mV的钳制电位下为1380±340 pA/细胞）或喂食高钾饮食1周（670±260 pA/细胞）时则很大。在这两种情况下，CNT细胞中的电流比同一动物CCT细胞中的电流大两到四倍。在醛固酮处理的动物中，初始集合管（iCT）细胞中的电流处于中间水平，使得INa的相对大小如下：CNT > iCT > CCT。对结果的定量分析表明，CNT集合群体重吸收Na的最大能力可能高达18 μmol/min，约占Na滤过负荷的10%。该能力比CCT高约10倍。
