Neumann K H, Rector F C
J Clin Invest. 1976 Nov;58(5):1110-8. doi: 10.1172/JCI108563.
The role of chloride concentration gradients in proximal NaCl and water reabsorption was examined in superficial proximal tubules of the rat by using perfusion and collection techniques. Reabsorptive rates (Jv), chloride concentrations, and transtubular potential difference were measured during perfusion with solutions (A) simulating an ultrafiltrate of plasma; (B) similar to (A) except that 20 meq/liter bicarbonate was replaced with acetate; (C) resembling late proximal fluid (glucose, amino acid, acetate-free, low bicarbonate, and high chloride); and (D) in which glucose and amino acids were replaced with raffinose and bicarbonate was partially replaced by poorly reabsorbable anions (cyclamate,sulfate, and methyl sulfate). In tubules perfused with solutions A and B, Jv were 2.17 and 2.7 nl mm-1 min-1 and chloride concentrations were 131.5 +/- 3.1 and 135 +/- 395 meq/liter, respectively, indicating that reabsorption is qualitatively similar to free-flow conditions and that acetate adequately replaces bicarbonate. With solution C, Jv was 2.10 nl mm-1 min-1 and potential difference was +1.5 +/- 0.2 mV, indicating that the combined presence of glucose, alanine, acetate, and bicarbonate per se is not an absolute requirement. Fluid reabsorption was virtually abolished when tubules were perfused with D solutions; Jv was not significantly different from zero despite sodium and chloride concentrations similar to plasma; chloride concentration was 110.8 +/- 0.2 meq/liter and potential difference was -0.98 mV indicating that chloride was close to electrochemical equilibrium. These results suggest the importance of the chloride gradient to proximal tubule reabsorption in regions where actively reabsorbable solutes (glucose, alanine, acetate, and bicarbonate) are lacking and provide further evidence for a passive model of NaCl and water transport.
采用灌注和收集技术，研究了大鼠浅表近端小管中氯离子浓度梯度在近端氯化钠和水重吸收中的作用。在用以下溶液灌注期间，测量重吸收率（Jv）、氯离子浓度和跨管电位差：（A）模拟血浆超滤液的溶液；（B）与（A）相似，但用乙酸盐替代20毫当量/升的碳酸氢盐；（C）类似于近端晚期液体（无葡萄糖、氨基酸、乙酸盐、低碳酸氢盐和高氯离子）；以及（D）用棉子糖替代葡萄糖和氨基酸，并用难吸收阴离子（甜蜜素、硫酸盐和甲基硫酸盐）部分替代碳酸氢盐。在用溶液A和B灌注的小管中，Jv分别为2.17和2.7纳升·毫米⁻¹·分钟⁻¹，氯离子浓度分别为131.5±3.1和135±395毫当量/升，这表明重吸收在质量上与自由流动条件相似，且乙酸盐可充分替代碳酸氢盐。对于溶液C，Jv为2.10纳升·毫米⁻¹·分钟⁻¹，电位差为+1.5±0.2毫伏，这表明葡萄糖、丙氨酸、乙酸盐和碳酸氢盐的共同存在本身并非绝对必要条件。当用D溶液灌注小管时，液体重吸收几乎完全消除；尽管钠和氯离子浓度与血浆相似，但Jv与零无显著差异；氯离子浓度为110.8±0.2毫当量/升，电位差为-0.98毫伏，表明氯离子接近电化学平衡。这些结果表明，在缺乏主动重吸收溶质（葡萄糖、丙氨酸、乙酸盐和碳酸氢盐）的区域，氯离子梯度对近端小管重吸收很重要，并为氯化钠和水转运的被动模型提供了进一步证据。
