Renal cellular transport of exogenous glutathione: heterogeneity at physiological and pharmacological concentrations.
Properties and kinetics of GSH transport into proximal tubular (PT) and distal tubular (DT) cells from rat kidney were determined to validate further the hypothesis that cellular differences in handling of GSH contribute to the greater susceptibility of DT cells to oxidant injury. PT and DT cells were incubated with a broad range of GSH concentrations, encompassing physiologically relevant (0.001 to 0.1 mM) to pharmacological (0.25 to 5 mM) levels of GSH. GSH uptake in PT cells was rapid, exhibiting an overshoot with a maximum at 1-min incubation. GSH uptake in DT cells reached maximal intracellular levels at 2- to 5-min incubations. GSH uptake in PT cells was resolved into two kinetically distinct processes, with Km values of 41.7 and 540 microM and Vmax values of 183 and 4885 pmol/min per 10(6) cells. In contrast, GSH uptake in DT cells was best described by one process, with Km and Vmax values of 1480 microM and 2094 pmol/min per 10(6) cells, respectively. Rates of GSH synthesis from 1 mM precursor amino acids were approximately 3-fold faster in PT cells, but rates of cysteine accumulation were 3.5-fold faster in DT cells. Accumulation of intracellular GSH in PT cells was 8-fold faster after incubation with 1 mM GSH than after incubation with 1 mM precursor amino acids. At both a physiological (10 microM) and a pharmacological (5 mM) GSH concentration, uptake exhibited marked Na+ and energy dependence, sensitivity to substrates for the organic anion and dicarboxylate carriers, and sensitivity to various gamma-glutamyl amino acids in PT cells only. Na+-dependent GSH uptake in PT cells was accounted for completely by activity of the organic anion and dicarboxylate carriers. These results indicate that DT cells possess limited capacity to transport GSH and suggest that exogenous GSH may not be effective in protecting other segments of the nephron besides the PT region from oxidants or other agents that alter GSH status.
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Department of Pharmacology, Wayne State University School of Medicine, Detroit, MI 48201, USA. l.h.lash@wayne.edu
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D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D004305:Dose-Response Relationship, Drug; D005978:Glutathione / Q000096:biosynthesis / Q000378:metabolism*; D066298:In Vitro Techniques; D007686:Kidney Tubules, Distal / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
D000596:Amino Acids; D005978:Glutathione