Sodium-free fluid reabsorption in Necturus kidney perfused with sodium-free media

Abstract

Sodium-free fluid reabsorption in Necturus kidney perfused with sodium-free media. The ability of tubular epithelium to transport sodium-free fluid from lumen to the peritubular side was tested in the isolated Necturus kidney perfused in situ with sodium-free solutions. Each animal was perfused with a single solution. Perfusion rates were 0.11 ml/min (portal vein) and 0.21 ml/min (aorta). The standard Na solutions were a Ringer's bicarbonate and a Ringer's phosphate (Na, 95 mM; total osmolality, 200 mOsm). The substituted solutions were of similar composition to the control Ringer's phosphate in all but the Na content. Sodium was substituted by either lithium, potassium, rubidium, cesium or choline. Large split-drops were introduced into in the proximal tubule with an aliquot of the perfusing solution. In most experiments volume reduction was actually measured until at least one-half of the split-drop was reabsorbed. It was found that fluid transport proceeds in Na-free solutions, without important changes in reabsorptive rate. When ouabain was added to sodium and choline solutions, reabsorption was sharply reduced. The data suggest that transepithelial net movement, metabolically dependent, may occur in Necturus kidney perfused with Na-free media. Reabsorption tubulaire dans le rein de Necturus , perfuse avec des solutions depourvues de sodium. La capacite de l'epithelium tubulaire de reabsorber le fluide intra-tubulaire de la lumiere vers l'interstitium a ete etudiee dans le rein isole de Necturus , perfuse avec diverses solutions depourvues de sodium. Chaque animal a ete perfuse avec une seule solution. Les debits de perfusion etaient de 0.11 ml/min (veine porte) et 0.21 ml/min (aorte). Les solutions standard avec sodium etaient un Ringer bicarbonate et un Ringer phosphate (Na, 95 mM; osmolalite totale, 200 mOsm). Les solutions de substitution avaient la meme composition que le Ringer phosphate, a l'exception du sodium qui a ete remplace par du lithium, du potassium, du rubidium, du cesium ou de la choline. Un aliquot de la solution de perfusion a ete depose entre deux colonnes d'huile dans la lumiere tubulaire proximale. Dans la plupart des cas, la reduction du volume de la gouttelette a ete observee jusqu'a reabsorption de plus de sa moitie. Le transport se poursuit en l'absence de sodium, sans modification majeure de la vitesse de reabsorption. L'addition d'ouabaine dans les solutions de sodium et de choline reduit considerablement la reabsorption. Ces resultats suggerent qu'un transport transepithelial net, consommant de l'energie, peut avoir lieu dans le rein de Necturus perfuse avec des solutions depourvues de sodium.