D-penicillamine and the transport of L-cystine by rat and human renal cortical brush-border membrane vesicles.

Brush-border membrane vesicles (BBMV) were prepared from rat and human renal cortical tissue by magnesium aggregation and differential centrifugation, and the uptake of L-cystine, L-cysteine, and L-cysteine-D-penicillamine were assessed by a rapid-filtration technique. L-Cystine uptake was relatively sodium independent and associated with membrane binding. Sodium-stimulated uptake was sensitive to a cation but not anion diffusion potential. Both sodium-independent and sodium-stimulated uptake rates were inhibited by the cationic L-amino acids and by some neutral L-amino acids. The uptake rates of L-cysteine and L-cysteine-D-penicillamine were more sodium dependent, and sodium-stimulated uptake rates were more sensitive to cation and anion diffusion potentials. Neither the sodium-independent nor the sodium-stimulated uptake rates of L-cysteine or L-cysteine-D-penicillamine were inhibited by the cationic L-amino acids. L-Cysteine-D-penicillamine showed relatively little membrane binding. It is concluded that L-cystine is transported into renal cortical BBMV by pathways distinct from those concerned with the transport of L-cysteine and L-cysteine-D-penicillamine, and it is postulated that these differences may account for some of the effects of D-penicillamine in cystinuria.