Inhibition of renal Na+-Pi cotransporter by mercuric chloride: Role of sulfhydryl groups
✍ Scribed by Dr. Mahmoud Loghman-Adham
- Publisher
- John Wiley and Sons
- Year
- 1992
- Tongue
- English
- Weight
- 791 KB
- Volume
- 49
- Category
- Article
- ISSN
- 0730-2312
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✦ Synopsis
Abstract
We studied the role of sulfhydryl groups in Na^+^‐Pi contransport across the renal brush border membrane (BBM), using HgCl~2~, an agent which penetrates membranes freely. HgCl~2~ inhibited the initial Na^+^‐dependent ^32^Pi transport in a dose‐dependent manner (IC~50~ = 54 μM). Na^+^‐independent transport was not affected. The inhibitory effect persisted under Na^+^ equilibrium–exchange conditions. Additionally, HgCl~2~ had no effect on the diffusional uptake of ^22^Na up to 1 min incubation. Exposure to HgCl~2~ had no effect on vesicle integrity as determined by osmotic shrinking experiments. BBM vesicle (BBMV) volume, determined by D‐glucose equilibrium uptake, was not affected at low HgCl~2~ concentrations, but decreased at higher concentrations (> 100 μM). Vesicle volumes, determined by flow cytometry, were not changed after exposure to HgCl~2~. Kinetic studies showed a reduction in the apparent Vmax for Pi transport from 1.40 ± 0.13 to 0.75 ± 0.19 nmoles/mg protein/5 sec, without a significant change in the apparent Km. In protection studies, dithiothreitol (DTT) completely protected agaisnt inhibition, but Pi, phosphonoformic acid (PFA), and Na^+^ gave no protection. The data suggest that sulfhydryl groups are essential for the function of Na^+^‐Pi cotransporter of renal BBM.