Mechanisms of action of 2,3-dimercaptopropane-1-sulfonate and the transport, disposition, and toxicity of inorganic mercury in isolated perfused segments of rabbit proximal tubules.

Mechanisms by which the dithiol chelating agent 2, 3-dimercaptopropane-1-sulfonate (DMPS) significantly alters the renal tubular transport, accumulation, and toxicity of inorganic mercury were studied in isolated perfused pars recta (S2) segments of proximal tubules of rabbits. Addition of 200 microM DMPS to the bath provided complete protection from the toxic effects of 20 microM inorganic mercury in the lumen. The protection was linked to decreased uptake and accumulation of mercury. Additional data indicated that, when DMPS and inorganic mercury were coperfused through the lumen, very little inorganic mercury was taken up from the lumen. We also obtained data indicating that DMPS is transported by the organic anion transport system and that this transport is linked to the therapeutic effects of DMPS. Interestingly, very little inorganic mercury was taken up and no cellular pathological changes were detected when inorganic mercury and DMPS were added to the bath. We also tested the hypothesis that DMPS can extract cellular mercury while being transported from the bath into the luminal compartment. Our findings showed that, when DMPS was applied to the basolateral membranes of S2 segments after they had been exposed to mercuric conjugates of glutathione of the laminal membrane, the tubular content of mercury was greatly reduced and the rates of disappearance of mercury from the lumen changed from positive values to markedly negative values. We conclude that inorganic mercury is extracted from proximal tubular cells by a transport process involving the movement of DMPS from the bathing compartment to the luminal compartment.

Heterogeneity of glutathione synthesis and secretion in the proximal tubule of the rabbit.

This study was designed to examine the synthesis and possible secretion of glutathione (GSH) in the S1, S2, and S3 segments of the rabbit proximal tubule. GSH synthesis and secretion rates were measured in the three segments of the proximal tubule, using the isolated perfused renal tubule technique. Tritiated (3H) glycine was perfused into segments and synthesized [3H]GSH (3H on the glycine residue) was measured in the bathing solution, collectate, and tubule extract. In the S1 segments, GSH was synthesized at the rate of 8.65 +/- 0.88 fmol.min-1.mm-1 tubule length and preferentially secreted into the lumen at the rate of 7.28 +/- 0.74 fmol.min-1.mm-1. The difference between synthesis and secretion appeared in the bathing solution. The S2 segment synthesized GSH at the rate of 3.88 +/- 0.82 and secreted GSH at the rate of 2.78 +/- 0.57 fmol.min-1.mm-1. GSH synthesis and secretion rates in the S3 segment were 5.45 +/- 1.19 and 4.22 +/- 1.16 fmol.min-1.mm-1, respectively. Cellular concentrations of [3H]GSH increased along the length of the proximal tubule, with the highest concentrations in the S3 segment. The respective GSH cellular concentrations in the S1, S2, and S3 segments were 35.89 +/- 10.51, 49.65 +/- 9.32, and 116.90 +/- 15.76 microM. These findings indicate that there is heterogeneity of GSH synthesis along the proximal tubule and that synthesized GSH is secreted preferentially into the lumen.