Physiologic concentrations of zinc affect the kinetics of copper uptake and transport in the human intestinal cell model, Caco-2

Copper uptake was enhanced and copper transport was reduced in Caco-2 cells cultured in media containing high concentrations of zinc. Here we show that physiologic zinc concentrations also affect copper movement into and out of Caco-2 cells. Cells were seeded onto Falcon membranes with high pore density and maintained in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum, nonessential amino acids, glucose and glutamine. In one experiment, the cells were exposed to media containing either 5 or 25 micromol zinc/L from d 14 to 21 after seeding. Then, copper uptake and transport, in both apical and basolateral directions, were measured by using 64Cu. Cells exposed to 25 micromol zinc/L had a 25% higher (P < 0.05) uptake of 64Cu from the apical side than those exposed to 5 micromol zinc/L. There was no effect of zinc on 64Cu uptake from the basolateral side, even though the amount of label taken up was as much as threefold higher (P > 0.05) than from the apical side. Transport of 64Cu across the cell layer in both directions was 50% less (P < 0.05) in cells exposed to 25 micromol zinc/L vs. 5 micromol zinc/L. In another experiment, zinc-exposed cells were labeled with 64Cu and efflux of the label to the apical and basolateral sides was measured over time. The rate of efflux to the apical side was linear and not affected by zinc. However, there was a 37% reduction (P < 0.05) in 64Cu efflux to the basolateral side by the higher zinc concentration. Curve-fit analysis showed that the basolateral efflux was made up of an exponential and a linear component. Cellular zinc concentrations were proportional to the zinc concentrations in the media. Although the data suggest that high media zinc inhibited the copper efflux transporter and enhanced the influx transporter, copper did not accumulate in the cell.