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.
Tacnet
F
F
Département de Biologie Cellulaire et Moléculaire, SBCe, C.E. de Saclay, Gif sur Yvette, France.
Lauthier
F
F
Ripoche
P
P
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D017920:Antiporters / Q000378:metabolism; D002713:Chlorine; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D007474:Ion Exchange; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D009842:Oligopeptides / Q000378:metabolism; D011868:Radioisotopes; D013552:Swine; D015032:Zinc / Q000378:metabolism* / Q000493:pharmacokinetics; D017967:Zinc Compounds / Q000378:metabolism; D015037:Zinc Radioisotopes; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D017920:Antiporters; D009842:Oligopeptides; D011868:Radioisotopes; D017967:Zinc Compounds; D015037:Zinc Radioisotopes; D062367:ortho-Aminobenzoates; D002713:Chlorine; C037026:diglycyl-histidine; C001209:fenamic acid; D015032:Zinc; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid