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Mechanisms of zinc transport into pig small intestine brush‐border membrane vesicles.
Author(s) -
Tacnet F,
Lauthier F,
Ripoche P
Publication year - 1993
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1993.sp019666
Subject(s) - dids , antiporter , chemistry , brush border , cotransporter , zinc , vesicle , biophysics , ion transporter , membrane transport , electrochemical gradient , osmotic concentration , nigericin , valinomycin , biochemistry , membrane , sodium , biology , organic chemistry
1. The purpose of the present work was to examine certain membrane transport mechanisms likely to carry zinc across the brush‐border membrane of pig small intestine, isolated in a vesicular form. 2. In initial velocity conditions, saturation kinetics revealed a great effect of pH on zinc transport: optimal conditions were observed with an intravesicular pH of around 6.6 with or without a H+ gradient; however, this did not allow us to conclude the existence of a neutral exchange between Zn2+ and H+ ions. 3. By measuring 36Cl uptakes, the presence of the Cl(‐)‐HCO3‐ or Cl(‐)‐OH‐antiporter with typical 4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid (DIDS) sensitivity was detected in vesicles; zinc did not alter this anionic exchange activity. A 65Zn time course, performed in conditions identical with those for 36Cl uptake, was DIDS insensitive and was greatly inhibited by an outward OH‐ gradient. This could argue against a transport of zinc as a complex with Cl‐ and HCO3‐ through the anion antiporter. 4. When external Cl‐ and HCO3‐ were replaced by SCN‐, able to form a Zn(SCN)4(2‐) complex, we observed a stimulating effect of outward HCO3‐ gradients on 65Zn uptake but neither DIDS nor diphenylamine‐2‐carboxylate (DPC) inhibited the transport in these conditions. This suggested that the intestinal anion antiporter was not a major route for zinc reabsorption. 5. The tripeptide Gly‐Gly‐His at low concentrations stimulated 65Zn uptake, then inhibited it in a dose‐dependent manner either in the presence of an inward H+ gradient or in the presence of a membrane potential ‘negative inside’ or in both situations. These conditions are necessary for the active transport of the peptide and this strongly suggests that zinc can be transported as a [Gly‐Gly‐His‐Zn] complex, utilizing the peptide carrier system.