Ellison D H, Velázquez H, Wright F S
Department of Medicine, Yale University School of Medicine, West Haven, Conn.
Miner Electrolyte Metab. 1987;13(6):422-32.
The distal tubule contributes importantly to renal sodium and chloride reabsorption and potassium secretion. Changes in various factors acting from the luminal or basolateral side of the distal tubule can alter rates of net ion transport. Experiments were designed to examine some of the factors of luminal fluid that can alter sodium, chloride and potassium transport rates. This was accomplished by employing in vivo microperfusion techniques to change luminal sodium, potassium and chloride concentrations and fluid flow rate independent of any effects on systemic homeostatic mechanisms. Results of these experiments indicate that increasing the rate of fluid flow in the distal tubule, within the physiologic range, stimulates potassium secretion, even when sodium concentration does not change. Low sodium concentrations inhibit net potassium secretion only when they are below those that have been measured in this segment under physiologic conditions. Potassium secretion rates increase significantly when the luminal chloride concentration is reduced, an effect that can be dissociated from changes in transepithelial voltage. Sodium absorption is limited by low luminal chloride concentration and chloride absorption is limited by low luminal sodium concentration. These results and others have led us to postulate that at least four different pathways mediate Na, K and Cl transport across the luminal membrane of distal tubule cells. Two pathways permit diffusive movement of cations, one an amiloride inhibitable channel for sodium, the other a barium inhibitable channel for potassium. Two other pathways appear to mediate coupled K-Cl secretion and Na-Cl absorption across the apical membrane of distal tubule cells. A new model of apical membrane transport pathways in the distal tubule is presented.
远曲小管对肾脏钠和氯的重吸收以及钾的分泌起着重要作用。作用于远曲小管管腔侧或基底外侧的各种因素发生变化时，可改变离子净转运速率。本实验旨在研究一些可改变管腔液中钠、氯和钾转运速率的因素。这是通过采用体内微灌注技术来改变管腔钠、钾和氯浓度以及液体流速实现的，且该技术不会对全身稳态机制产生任何影响。这些实验结果表明，在生理范围内增加远曲小管内的液体流速可刺激钾的分泌，即便钠浓度不变。低钠浓度仅在低于生理条件下该节段所测得的浓度时，才会抑制钾的净分泌。当管腔氯浓度降低时，钾分泌速率显著增加，这一效应与跨上皮电压的变化无关。钠的重吸收受管腔低氯浓度限制，而氯的重吸收受管腔低钠浓度限制。这些结果及其他研究结果使我们推测，至少有四条不同的途径介导远曲小管细胞管腔膜上的钠、钾和氯转运。两条途径允许阳离子进行扩散运动，一条是对阿米洛利敏感的钠通道，另一条是对钡敏感的钾通道。另外两条途径似乎介导远曲小管细胞顶端膜上钾 - 氯的协同分泌和钠 - 氯的吸收。本文提出了远曲小管顶端膜转运途径的新模型。
