Mechanisms of zinc transport into pig small intestine brush‐border membrane vesicles.

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.