Zinc uptake and transcellular movement by CACO-2 cells: Studies with media containing fetal bovine serum

Abstract

A series of experiments using CACO-2 cells, have been conducted to describe the cellular events occurring during Zn uptake and transcellular movement in the presence of media containing fetal bovine serum (FBS). CACO-2 cells were grown for 21 days on either T-25 cell culture flasks or semipermeable membrane inserts maintained in six-well culture plates. Experiments were then conducted using normal growth medium containing FBS, to which 65Zn was added. The rate of Zn transport in an apical to basolateral direction was much greater than the rate in the opposite direction. To study whether uptake and movement exhibited saturation kinetics, different concentrations of Zn (1–200 μ m ) were added with 65Zn. Uptake at the basolateral membrane was saturable; apical to basolateral movement, basolateral to apical movement, and uptake at the apical membrane were not. 65Zn moved apically to basolaterally at a small but constant rate regardless of the basolateral concentration of Zn. The binding ligands for Zn in the cytosol differed depending on the prior Zn status of the cell and the time postlabeling. Endogenous 65Zn was released to the apical and basolateral sides at different rates. These data confirm a previous report that uptake and transcellular movement of Zn is different at the apical and basolateral membrane, and they further show that the presence of Zn-binding ligands alters these processes.