Reexamination of the interplay between dibasic amino acids and I-cystine/L-cysteine during tubular reabsorption.

Abstract

Interactions of L-cysteine (= cys) and L-cystine (= cys-cys), and dibasic amino acids were investigated during tubular reabsorption by microperfusion experiments in rat kidney. The following results were obtained: The dibasic amino acids L-ornithine and L-canavanine were strong inhibitors of cys-cys reabsorption. The arginine analogue agmatine and the lysine analogue 2,6-diaminopimelic acid had no effect. The oxidizing agent azodicarboxylic acid bis-dimethylamide (= diamide) decreased the fractional reabsorption rate (= FRR) of cys-cys (0.08 mmol X l-1) from 84% to 60% when present in the perfusion fluid in a concentration of 10 mmol X l-1. Diamide did not affect the reabsorption of a dibasic amino acid (L-arginine) nor of a neutral amino acid (L-phenylalanine). The FRR of L-arginine and L-ornithine could not be decreased by adding cys-cys to the perfusion fluid. Cys had just as little effect on the reabsorption of L-arginine like agmatine. In the presence of alpha-aminoisobutyric acid a slight reduction of the FRR of L-arginine could be observed. The dibasic amino acids L-arginine and L-canavanine had no influence on the FRR of cys when dithioerythritol was added to the perfusion fluid. More than one site exists for tubular reabsorption of cys-cys. One of these may be shared by dibasic amino acids. Cys is reabsorbed by a separate and specific transport system. A reduction of cys-cys to cys takes place rather in the tubular cell than in the lumen.