EVIDENCE FOR ACTIVE CHLORIDE REABSORPTION IN THE DISTAL RENAL TUBULE OF THE RAT*

Abstract

The mechanism of Cl- reabsorption in the distal tubule was examined by determining the relationshp between the distal transtubular potential difference (ET) and the ratio of peritubular Cl" concentration, [Cl]p, to distal tubular fluid Cl" concentration, [Cl]T. F , in normal and salt-depleted rats during Na2SO4 diuresis. The [Cl]T.F. fell to very low levels as fluid passed through the distal tubule. Fifteen per cent of all [C1]t.f. was below a level (1 mEq per L) that could result from the highest ET (- 120mv) if passive reabsorption were solely responsible. Ninety-five % of all [C1]x.f. fell below the level that could be produced by the ET measured in the same tubule from which the chloride sample was obtained. It is concluded, therefore, that in the distal tubule chloride is actively reabsorbed against electrochemical gradients.