Sodium conductance changes by aldosterone in the rat kidney.

Abstract

To asses passive permeability properties of distal, and proximal tubules of the rat kidney the tubular lumen was perfused with solutions of 1.5 and 150 mM Na/l while transtubular potential differences were recorded. Sodium transport numbers (T Na) were calculated.T Na in the distal tubule of adrenalectomized rats was acutely increased from 0.21 to 0.27 by aldosterone (5 μg/100 g B.W.). This effect of aldosterone could not be reduced by concomitant injection of cycloheximide (100 μg/100 g B.W.). Aldosterone was also effective in control rats. In the proximal tubule similar data were obtained. However, the aldosterone-induced increase of conductance was slightly reduced with cycloheximide. These measurements of transepithelial sodium conductance indicate that aldosterone, in addition to the already known stimulation of active sodium transport, increases overall permeability of the tubular wall to sodium. In the distal tubule this effect indicates an increase of the luminal membrane permeability whereas in the proximal tubule aldosterone may facilitate the diffusion of sodium through the intercellular shunt path and/or the luminal membrane. The passive components of transepithelial electrolyte transfer seem to be less sensitive to inhibition of protein synthesis than the active transport components.