Mechanism of mercurial inhibition of sodium-coupled alanine uptake in liver plasma membrane vesicles from Raja erinacea

Journal Article · Fri Feb 01 00:00:00 EST 1991 · Toxicology and Applied Pharmacology; (USA)

DOI:https://doi.org/10.1016/0041-008X(91)90216-2· OSTI ID:6139209

Sellinger, M; Ballatori, N; Boyer, J L ^[1]

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1. Mount Desert Island Biological Laboratory, Salsbury Cove, ME (USA)

In mammalian hepatocytes the L-alanine carrier contains a sulfhydryl group that is essential for its activity and is inhibited by mercurials. In hepatocytes of the evolutionarily primitive little skate (Raja erinacea), HgCl2 inhibits Na(+)-dependent alanine uptake and Na+/K(+)-ATPase and increase K+ permeability. To distinguish between direct effects of HgCl2 on the Na(+)-alanine cotransporter and indirect effects on membrane permeability, (3H)alanine transport was studied in plasma membrane vesicles. (3H)Alanine uptake was stimulated by an out-to-in Na+ but not K+ gradient and was saturable confirming the presence of Na(+)-alanine cotransport in liver plasma membranes from this species. Preincubation of the vesicles with HgCl2 for 5 min reduced initial rates of Na(+)-dependent but not Na(+)-independent alanine uptake in a dose-dependent manner (10-200 microM). In the presence of equal concentrations of NaCl or KCl inside and outside of the vesicles, 75 microM HgCl2 directly inhibited sodium-dependent alanine-(3H)alanine exchange, demonstrating that HgCl2 directly affected the alanine cotransporter. Inhibition of Na(+)-dependent alanine uptake by 30 microM HgCl2 was reversed by dithiothreitol (1 mM). HgCl2 (10-30 microM) also increased initial rates of 22Na uptake (at 5 sec), whereas 22Na uptake rates were decreased at HgCl2 concentrations greater than 50 microM. Higher concentrations of HgCl2 (100-200 microM) produced nonspecific effects on vesicle integrity. These studies indicate that HgCl2 inhibits Na(+)-dependent alanine uptake in skate hepatocytes by three different concentration-dependent mechanisms: direct interaction with the transporters, dissipation of the driving force (Na+ gradient), and loss of membrane integrity.

• OSTI ID: 6139209
• Journal Information: Toxicology and Applied Pharmacology; (USA), Vol. 107:2; ISSN 0041-008X
• Country of Publication: United States
• Language: English

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ANIMALS
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BETA DECAY RADIOISOTOPES
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BODY
CARBOXYLIC ACIDS
CELL CONSTITUENTS
DIGESTIVE SYSTEM
ELEMENTS
ENZYMES
GLANDS
HYDROGEN COMPOUNDS
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ISOMERIC TRANSITION ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
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ORGANIC ACIDS
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ORGANS
PHOSPHOHYDROLASES
RADIOISOTOPES
SODIUM ISOTOPES
VERTEBRATES
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