Laboratory Investigation

Kidney International (1972) 2, 66–75; doi:10.1038/ki.1972.73

Influence of serum proteins on net fluid reabsorption of isolated proximal tubules

Jared J Grantham1, Patti B Qualizza1 and Larry W Welling1

1Departments of Medicine and Pathology, University of Kansas Medical Center, Kansas City, Kansas

Correspondence: Dr Jared J Grantham, Department of Medicine, University of Kansas Medical Center, Kansas City, Kansas 66103, U.S.A.

Received 16 March 1972; Accepted 15 May 1972.

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Abstract

Influence of serum proteins on net fluid absorption of isolated proximal tubules. To determine the direct effect on net fluid absorption of serum proteins in the peritubular fluid, isolated segments of proximal convoluted (PCT) and straight (PST) tubules were studied in vitro. The tubular lumen was perfused at one end with a micropipet; the other end was occluded. Net transtubular isosmotic fluid absorption at 37° C was determined from the clearance of 3H2O out of the perfusion pipet. In a bath of rabbit serum or 6 g/100 ml bovine albumin in Ringer's media, net absorption was approximately three-fold greater in PCT's than in PST's. Net absorption was directly proportional to tubular length and was markedly inhibited by ouabain. Increased intralumenal hydrostatic pressure did not affect net absorption significantly. Rapid lowering of the bath protein to less than 6 g/100 ml caused net absorption to decrease; in both proximal convoluted and straight tubules net absorption was reduced about 40% in a bath containing 0.3% serum protein. When the bath protein was increased from 6% to 10%, net fluid absorption decreased slightly. On the basis of these studies we conclude that net fluid absorption of proximal tubules is relatively independent of the difference in either hydrostatic or oncotic pressure between the tubular lumen and peritubular fluid. It is suggested that peritubular serum proteins may influence net absorption at the antilumenal side of the epithelial cell, perhaps by facilitating the movement of absorbate across the tubular basement membrane.

Influence des protéines du sérum sur l'absorption nette de liquide par les tubes proximaux isolés. Afin de déterminer l'effet direct des protéines du sérum sur l'absorption nette de liquide, des segments isolés de tube contourné proximal (PCT) et de tube droit (PST) ont été étudiés in vitro. La lumière tubulaire a été perfusée a une extrémité au moyen d'une micropipette, l'autre extrémité a été occluse. L'absorption nette et iso osmotique de liquide à 37° C a été déterminée à partir de la clearance de 3H2O à la sortie de la pipette de perfusion. Dans un bain de sérum lapir ou dans un Ringer contenant 6.0 g/100 ml d'albumine bovine l'absorption nette était approximativement 3 fois plus grande dans le PCT que dans le PST. L'absorption nette était directement proportionnelle à la longueur du segment tubulaire et était nettement inhibée par l'ouabaïne. L'augmentation de la pression hydrostatique intraluminale n'a pas affecté l'absorption significativement. La diminution rapide de la concentration de protéines dans le bain à moins de 6.0 g/100 ml a déterminé une diminution de l'absorption nette. Celle-ci était réduite d'environ 40%, aussi bien dans PCT que PST, dans un bain contenant 0.3 g/100 ml de protéines. Quand la concentration des protéines du bain a été augmentée de 6% à 10% l'absorption nette a légèrement diminué. Sur la base de ces résultats nous concluons que l'absorption nette de liquide par les tubes proximaux est relativement indépendante de la différence soit des pressions hydrostatiques soit des pressions oncotiques entre la lumière tubulaire et le liquide péritubulaire. Il est suggéré que les protéines sériques péritubulaires peuvent influencer l'absorption nette du côté antiluminal de la cellule épithéliale, peut-être en facilitant le mouvement de l'absorbat à travers la membrane basale tubulaire.

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