Regulation of copper uptake and transport in intestinal cell monolayers by acute and chronic copper exposure

Adaptation to high and low copper intake in mammals depends on the cellular control of influx, efflux and storage mechanisms of cellular copper concentrations. In the present study, we used an intestinal cell line (Caco-2), grown in bicameral chambers to study the effect of equilibrium loading with copper. We analyzed (64)Cu uptake from the apical surface, intracellular metal (Cu, Zn, Fe) content, (64)Cu transport into the basal chamber, and total copper, zinc and iron in the basal chamber. We found that the (64)Cu uptake is saturable, shows a linear response phase up to 1.5 microM reaching a plateau at 4-6 microM extracellular Cu. Intracellular copper increased 21.6-fold, from 1.5 to 32.4 mM (at 0.2-20.2 microM extracellular copper respectively). The time course for (64)Cu uptake and transport was linear when the cells were incubated with different copper concentrations. Uptake increased 10-fold when intracellular copper concentration was raised. Fluxes were lowest at 1.5 mM and highest at 32.4 mM Cu intracellular copper (2.03 and 20. 98 pmole (64)Cu insert(-1) h(-1), respectively). The apical-to-basolateral copper transfer rate was lower at 32.4 mM as compared to 1.5 mM intracellular copper (0.55-1.95 pmole (64)Cu insert(-1) h(-1), respectively). The total copper in the basal chamber increased 4.2-fold (from 3.04 to 12.85 pmole Cu insert(-1) h(-1)) when the intracellular copper concentration was raised. If cells are preincubated in a low copper medium most of the newly incorporated copper (64%) is transferred to the basolateral compartment. In contrast, under preloading with high copper concentration, only 4% of the fresh copper is transferred to the basal chamber; however, the intracellular copper contribution to this chamber increases by 4.2-fold. Thus, the process results in an increase in both storage and intracellular-to-basolateral flux of copper. In summary, our results indicate that copper fluxes from apical-to-cell and apical-to-basolateral domains are affected by intracellular copper concentration suggesting that mechanisms of copper transport involved in cellular adaptation to low and high copper exposure are different.