title: Pre-treatment of Caco-2 cells with zinc during the differentiation phase alters the kinetics of zinc uptake and transport(2).
abstract: The Caco-2 cell model was used to study the efficiency of absorption and endogenous excretion of zinc (Zn) regulated by dietary Zn concentration. Cells were seeded onto high pore-density membranes and maintained in medium supplemented with 10% FBS. After confluence, cells were treated with 5 or 25 &mgr;mol Zn/L for 7 d, and Zn uptake and transport were measured in both apical (AP) and basolateral (BL) directions by using (65)Zn. Similar cells were labeled with (65)Zn and the release of Zn to the AP and BL sides was measured. The AP uptake of Zn in cells exposed to 25 &mgr;mol Zn/L was slower (p < 0.05) than that in cells exposed to 5 &mgr;mol Zn/L. The AP to BL transport rate in the 25 &mgr;mol Zn/L group was only 40% (p < 0.05) of that in the 5 &mgr;M group. In contrast, the rate of BL Zn uptake was 4-fold higher in cells treated with 25 &mgr;mol Zn/L than in those treated with 5 &mgr;mol Zn/L (p < 0.05). The BL to AP transport rate was 2-fold higher in cells treated with 25 &mgr;mol Zn/L than in those treated with 5 &mgr;mol Zn/L (p < 0.05). Basolateral uptake was 6 to 25 times greater (p < 0.05) than AP uptake for cells treated with 5 and 25 &mgr;mol Zn/L, respectively. The rate of Zn release was enhanced about 4-fold (p < 0.05) by 25 &mgr;mol Zn/L treatment. Release to the BL side was 10 times greater than to the AP side. Zn-induced metallothionein (MT), thought to down-regulate AP to BL Zn transport, was 4-fold higher (p < 0.001) in the 25 &mgr;mol Zn/L group than in the 5 &mgr;M group, but the rate of BL Zn release was higher in cells treated with 25 &mgr;mol Zn/L than in those treated with 5 &mgr;mol Zn/L (p < 0.05). Induced changes in transport rates by media Zn concentrations could involve the up- and/or down-regulation of Zn influx and efflux proteins such as the ZIP and ZnT families of Zn transporters.
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, 58202-9034, Grand Forks, ND, USA
authors.forename: Philip G.
authors.initials: PG
authors.lastname: Reeves
authors.forename: Mary
authors.initials: M
authors.lastname: Briske-Anderson
authors.forename: LuAnn
authors.initials: L
authors.lastname: Johnson