NA-DEPENDENT TRANSPORT OF S-(1,2-DICHLOROVINYL)-L-CYSTEINE BY RENAL BRUSH-BORDER MEMBRANE-VESICLES

Cytotoxicity after exposure to the nephrotoxicant S-(1,2-dichloro-viny l)-L-cysteine (DCVC) requires transport of this cysteine conjugate acr oss the cell membrane. Although several basolateral transport pathways have been implicated in the uptake of this compound into renal proxim al cells, the identity of the process or processes associated with tra nsport across the luminal membrane is unclear. We used a preparation o f luminal brush-border membrane vesicles to characterize the transport of [S-35]DCVC in rabbit kidney. An inwardly directed Na-gradient stim ulated the initial rate of DCVC uptake by 16-fold compared to uptake m easured in the absence of Na+. The Na-dependent component of DCVC upta ke was stimulated by imposition of an inside-negative electrical poten tial difference and was blocked by the presence of 5 mM unlabeled DCVC in the extravesicular solution. Transport of DCVC was adequately desc ribed by Michaelis-Menten kinetics with an apparent K-t of 0.5 mM. DCV C uptake was blocked by the presence in the extravesicular solution of 10 mM concentrations of phenylalanine, leucine and cysteine, but not by glycine, proline, lysine, taurine, N-acetyl DCVC, p-aminohippurate, lactate or succinate. Unlabeled DCVC inhibited uptake of [C-14]phenyl alanine by a mechanism that exerted a greater effect on the apparent K -t than on the J(max) of phenylalanine, implicating a possible competi tive interaction between these compounds. The carrier-mediated permeab ility of DCVC (defined as the ratio of J(max)/K-t) in luminal brush bo rder membranes was as large as or larger than that reported for a batt ery of other organic electrolytes, including several amino acids and o rganic anions. We conclude that luminal transport of DCVC in rabbit pr oximal cells is limited to a single Na-cotransport process that also h andles phenylalanine.