Regulation of copper uptake and transport in intestinal cell monolayers byacute 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 concen trations. In the present study, we used an intestinal cell line (Caco-2), g rown in bicameral chambers to study the effect of equilibrium loading with copper. We analyzed Cu-64 uptake from the apical surface, intracellular met al (Cu, Zn, Fe) content, Cu-64 transport into the basal chamber, and total copper, zinc and iron in the basal chamber. We found that the Cu-64 uptake is saturable, shows a linear response phase up to 1.5 mu M reaching a plate au at 4-6 mu M extracellular Cu. Intracellular copper increased 21.6-fold, from 1.5 to 32.4 mM (at 0.2-20.2 mu M extracellular copper respectively). T he time course for Cu-64 uptake and transport was linear when the cells wer e 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 Cu-64 insert(-1) h(-1), respectively). The apical-to-basolateral copper tra nsfer rate was lower at 32.4 mM as compared to 1.5 mM intracellular copper (0.55-1.95 pmole Cu-64 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 copp er (64%) is transferred to the basolateral compartment. In contrast, under preloading with high copper concentration, only 4% of the fresh copper is t ransferred to the basal chamber; however, the intracellular copper contribu tion 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 concent ration suggesting that mechanisms of copper transport involved in cellular adaptation to low and high copper exposure are different. (C) 2000 Elsevier Science B.V. All rights reserved.