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

Abstract

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[Formula: see text]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−1tubule 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[Formula: see text]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 μM. These findings indicate that there is heterogeneity of GSH synthesis along the proximal tubule and that synthesized GSH is secreted preferentially into the lumen.

Toxicological significance of renal Bcrp: Another potential transporter in the elimination of mercuric ions from proximal tubular cells

“…Mrp2 has been shown to utilize GSH as a co-factor for the transport of certain substrates (Leslie et al , 2001; Leslie et al , 2005); therefore, it is possible that GSH- S -conjugates of Hg 2+ formed within proximal tubular cells can be secreted into the lumen via Mrp2. It is important to note that the synthesis and secretion of GSH have been shown to be greater in S1 segments than in S2 and S3 segments (Parks et al , 1998). Thus, it is possible that Hg 2+ within cells of S1 segments binds to GSH to form a GSH- S -conjugate, which can then be transported into the tubular lumen via Mrp2.…”

Transepithelial transport and metabolism of glycine in S1, S2, and S3 cell types of the rabbit proximal tubule

“…(5,16,17,(22)(23)(24)28) and was described previously (20). Briefly, samples generated from perfusion experiments were placed in microcentrifuge tubes with 800 l of artificial perfusion media and 100 l of a standard solution containing 1.3 mM of GSH, GSSG, glycine, and cysteine-glycine dissolved in 40 mM Li2CO3 at pH 9.5.…”

“…The mechanism for this protection has not been definitively determined. The second is that glycine is incorporated into the tri-amino acid GSH (20). GSH is the most abundant antioxidant in cells (5-10 mM).…”

“…Metabolism H radiolabel in the convoluted (S1) segments was recovered under the chromatographic peak corresponding to GSH (20). [ 3 H]GSH was present in the cellular and luminal samples, implying that GSH, and possibly other peptides, could be synthesized and secreted into the lumen (20).…”

“…[ 3 H]GSH was present in the cellular and luminal samples, implying that GSH, and possibly other peptides, could be synthesized and secreted into the lumen (20). The 3 H that appeared in the bathing solution samples was predominantly (95-97%) associated with the glycine HPLC peak.…”