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Evidence for Cadmium Uptake through Nramp2: Metal Speciation Studies with Caco-2 Cells

https://doi.org/10.1006/bbrc.2001.5245Get rights and content

Abstract

The specific uptake of 0.3 μM 109Cd by the TC7 clone of the human enterocytic-like Caco-2 cells increased 4-fold as the pHout was lowered from 7.5 to 5.5; the stimulatory effect of acidic media being more pronounced when the level of the free ion 109Cd2+, relative to total 109Cd, was increased. The initial uptake rate was 12-fold higher under conditions, optimizing 109Cd2+ accumulation over that of 109CdCl2−nn (NO3/pHout 5.5); a saturable system of transport has been characterized (Km = 1.1 ± 0.1 μM, Vmax = 87 ± 3 pmol/3 min/mg protein). An excess of Fe2+ failed to affect 109Cd uptake when the pHout was 7.4, whereas a strong inhibition was observed under NO3/pHout 5.5 conditions. In contrast, the maximal inhibitory effect of Zn2+ was observed under Cl/pHout 7.4 conditions. This results strongly suggest that Fe2+ may compete with Cd2+ for Nramp2, whereas Zn and CdCl2−nn compete for another system of transport that has yet to be identified.

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