The apical uptake of 64CuCl2 was investigated in human differentiated intestinal Caco-2 cells grown on permeable supports. At pH 6.0 in the apical compartment, the uptake of copper was linear over the first 6 min and between 10 and 80 microM CuCl2 exhibited non-saturable transport kinetics. In addition, copper uptake was energy-independent, affected by the valency state of copper, preferring Cu(II) over Cu(I), and not influenced by high (10 mM) extracellular calcium. The intracellular distribution of copper was investigated by FPLC at different times of uptake ('pulse') and of 'chase'. Intracellular copper initially bound predominantly to low molecular weight components (i.e., glutathione). and subsequently shifted to higher molecular weight components such as metallothionein and Cu,Zn superoxide dismutase.