Electrogenic uptake of d-imino acids by luminal membrane vesicles from rabbit kidney proximal tubule

Abstract

Some characteristics of electrogenic uptake of d-proline and hydroxy- d-proline by luminal membrane vesicle isolated either from pars convoluta or from pars recta of rabbit proximal tubule were indirectly studied by the spectrophotometric method. In vesicles from pars convoluta, the uptake of d-imino acids was mediated by both Na +-dependent and Na +-independent, but electrogenic processes. Indirect evidence for coupling between d-imino acids and H + fluxes was obtained by the following observations: (1) Addition of the H + ionophore (FCCP) to the vesicle-dye (3,3′-diethyloxadiocarbcyanine iodide) suspension completely abolished the Na +-independent electrogenic uptake of d-proline and hydroxy- d-proline by membrane vesicles from pars convoluta. (2) Addition of a relatively low concentration of d-proline in the incubation system decreased the H +-gradient dependent renal uptake of radioactive l-proline to approx. 60% of the control value. By contrast, the uptake of d-proline in vesicles from pars recta was strictly Na +-dependent, since no transient depolarization of membrane vesicles was ever observed in the absence of Na +. A comparison between the transport characteristics of d-imino acids and their naturally occurring l-isomers indicated that these compounds probably share common transport systems located along the proximal tubule of rabbit kidney.