|Briske Anderson, Mary|
Submitted to: Experimental Biology
Publication Type: Abstract Only
Publication Acceptance Date: April 17, 1999
Publication Date: N/A
Technical Abstract: The efficiency of absorption and endogenous excretion of zinc (Zn) are up- or down-regulated by dietary restriction or excess of zinc, respectively. The Caco-2 cell model was used to study this phenomenon. Cells were seeded onto Falcon membranes with high pore density and maintained in DME medium supplemented with 10% FBS, nonessential amino acids, glucose and glutamine. .This medium normally contains 5 uM Zn. In Exp I, the cells were exposed to 5 or 25 uM Zn from d 15 to 21. Then Zn uptake and transport were measured in both apical (AP) and basolateral (BL) directions by using 65**Zn in media with Zn concentrations similar to those in which the cells had been previously exposed. In Exp II, Zn exposed cells were labeled with 65**Zn and the release of label to the AP and BL sides were measured. The AP up- take rate of Zn into cells exposed to 25 uM Zn was not different than those exposed to 5 uM Zn; however, the AP to BL transport rate in the 25 uM group pwas reduced to only 34% of that in the 5 uM Zn group. In contrast, the rat of Zn uptake from the BL side was 4-fold greater in the 25 uM Zn group than in the 5 uM group. The transport rate from BL to AP was enhanced in the higher Zn group by about 3-fold. BL uptake was 50 times greater than AP uptake regardless of Zn concentration. The rate of Zn release from the cell was enhanced about 2-fold to the AP side and about 3-fold to the BL side by 25 uM Zn. Zn-induced metallothionine (MT) is thought to play a pivotal role in the regulation of AP to BL Zn transport by binding Zn. However, even though the MT concentration was 5-fold higher in the 25 uM Zn group than in the 5 uM group, the rate of Zn release from the cell was greater in the higher Zn group. Enhancement in the rate of Zn release by high media Zn may involve up-regulation of a Zn export protein such as ZnT-1.