Sodium-dependent transport of amino acids in renal brush border membrane vesicles and urinary free amino acid excretion in rats.

Abstract

The reabsorption of ammo acids in rat kidney was examined with respect to the Na+-gradient stimulated transport system. The time courses for the uptake of 14C-amino acids by brush border membrane vesicles were compared in the presence of either Na+ or K+ ions. The uptake of neutral amino acids was stimulated by the presence of a Na+-gradient and exhibited the typical overshoot phenomenon, whereas the uptake of acidic and basic amino acids was not clearly stimulated by Na+. The rate of Na+-dependent uptake into the vesicles at 1 min was determined for 20 amino acids, and was high for alanine, cysteine, valine and isoleucine but low in acidic and basic amino acids. In normal rat urine, the free forms of glycine, alanine and glutamic acid were excreted to a great extent, but isoleucine, arginine and sulfur-containing amino acids were excreted to a small extent. These results indicate that the urinary excretion of an amino acid is not necessarily correlated to the extent of its Na+-dependent uptake, and that other factors affecting the urinary excretion should also be considered.