Some aspects of proximal tubular sodium chloride reabsorption in Necturus kidney

Some aspects of proximal tubular sodium chloride reabsorption in Necturus kidney. Renal tubular reabsorption of fluid and sodium was measured by clearance methods in the doubly perfused Necturus kidney in which the bicarbonate concentration was varied between 0 and 60 mEq/liter. The effects of Diamox (2.2 × 10 -3 M), ouabain (10 -5 M) and ethacrynic acid (10 -4 M) and of acidosis were also investigated. In addition to clearance experiments, stationary microperfusion experiments were carried out on proximal tubules to measure volume flow and steady-state sodium and chloride concentration differences across the tubular epithelium. In some experiments, the transepithelial electrical potential difference was also measured using an axial electrode system. The following results were obtained: 1) Bicarbonate is not essential to the operation of renal tubular fluid and sodium transport. 2) Total renal and proximal tubular fluid and sodium transport are partially inhibited by Diamox, ouabain and ethacrynic acid. 3) The proximal tubule maintains a significant transepithelial sodium and chloride concentration difference and a significant electrical potential difference (lumen-negative) in the presence of a poorly permeant nonelectrolyte. The direction and magnitude of the electrical polarization fully accounts for the observed chloride concentration difference. The data support the thesis that sodium chloride transport across the proximal tubular epithelium takes place by active sodium transport and electrically coupled passive chloride reabsorption. Important species differences with respect to mammalian transport mechanisms are discussed. Quelques aspects de la reabsorption tubulaire proximale de chlorure de sodium par le rein du Necturus . La reabsorption tubulaire de sodium et d'eau a ete mesuree par les clearances dans le rein du Necturus doublement perfuse avec des concentrations de bicarbonate qui ont varie entre 0 et 60 mEq/litre. Les effets du Diamox (2,2 × 10 -3 M), de l'ouabaine (10 -5 M), de l'acide ethacrynique (10 -4 M) et de l'acidose ont ete etudies aussi. Outre les experiences de clearance, des experiences de microperfusion stationnaire ont ete realisees sur les tubes proximaux afin de mesurer le debit de liquide et les differences de concentration de sodium et de chlore de part et d'autre de l'epithelium tubulaire a l'equilibre. Dans quelques experiences la difference de potentiel trans-epitheliale a ete mesuree a l'aide d'un systeme d'electrode axiale. Les resultats suivants ont ete obtenus: 1) le bicarbonate n'est pas indispensable au transport tubulaire de sodium et d'eau; 2) la reabsorption renale globale et la reabsorption tubulaire proximale d'eau et de sodium sont partiellement inhibees par le Diamox, l'ouabaine et l'acide ethacrynique; 3) le tube proximal maintient une difference de concentration trans-epitheliale de sodium et de chlore et une difference de potentiel (lumiere negative) significatives en presence d'un corps non ionise peu permeant. Le sens et la grandeur de la polarisation electrique rendent completement compte de la difference de concentration de chlore qui est observee. Ces resultats sont en faveur de la these selon laquelle le transport de chlorure de sodium a travers l'epithelium tubulaire proximal a lieu par un transport actif du sodium et une reabsorption passive du chlore couplee electriquement.