Fujimoto M, Kubota T, Kotera K
Contrib Nephrol. 1977;6:114-23. doi: 10.1159/000399757.
Micropuncture study was performed in the proximal segment of bullfrog nephrons with double-barreled ion-sensitive microelectrodes to determine the electrochemical profile of K and Cl across the individual borders of tubular epithelium. The mean peritubular potential obtained was -68.4 mV, and the K activity in the plasma and the cell interior was 2.64 and 61.6 mEq/liter, respectively. The calculated equilibrium potential for K was 79.3 mV. Therefore, the cell K must be maintained by some K uptake mechanism against an electrochemical gradient of 11 mV. Further, the K activity of the tubular fluid was 2.92 mEq/liter and the actually measured PD across the brush border membrane was -55.7 mV. Since the calculated Nernst K potential is 76.8 mV, the K entry from lumen to cell must be done against an electrochemical gradient of 21.1 mV in the net. These facts might suggest a possibility of bilateral existence of K uptake mechanism in both the peritubular and brush border membranes of proximal tubular cells. In contrast, the Cl activity was measured to be 9.30, 78.0, and 72.5 mEq/liter for the cell, tubular fluid, and plasma, respectively. The Nernst Cl potentials calculated were 53.6 and 51.7 mV for the brush border and the peritubular membrane, the data being less than the actually determined values, 55.7 and 68.4 mV, respectively. Thus, the Cl ion seemed to distribute passively throughout its reabsorptive process in the bullfrog proximal tubule.
使用双管离子敏感微电极对牛蛙肾单位近端进行微穿刺研究，以确定钾离子和氯离子跨肾小管上皮细胞各边界的电化学分布。测得的平均管周电位为-68.4 mV，血浆和细胞内的钾离子活性分别为2.64和61.6 mEq/升。计算得出的钾离子平衡电位为79.3 mV。因此，细胞内的钾离子必须通过某种钾离子摄取机制来维持，以对抗11 mV的电化学梯度。此外，肾小管液中的钾离子活性为2.92 mEq/升，跨刷状缘膜实际测得的电位差为-55.7 mV。由于计算得出的能斯特钾电位为76.8 mV，钾离子从管腔进入细胞必须逆着21.1 mV的电化学梯度进行。这些事实可能表明，近端肾小管细胞的管周膜和刷状缘膜中都可能存在钾离子摄取机制。相比之下，测得细胞、肾小管液和血浆中的氯离子活性分别为9.30、78.0和72.5 mEq/升。计算得出的刷状缘膜和管周膜的能斯特氯离子电位分别为53.6和51.7 mV，这些数据低于实际测定值，分别为55.7和68.4 mV。因此，在牛蛙近端肾小管中，氯离子似乎在其重吸收过程中是被动分布的。
