Caco-2 cells on Snapwell® membranes and the Ussing chamber system as a model for cadmium transport in vitro

The transport of cadmium across Caco-2 monolayers in vertical alignment, in combination with the Ussing chamber technique, was investigated. The Caco-2 cells were grown in Dulbecco's Modified Eagle Medium and the cells were seeded on six-well Snapwell(R) polycarbonate inserts (Costar) at a density of 3 x 10(5) cells/cm(2). Accumulation and transport studies were performed after 14 days, when the cells had formed a monolayer. Cells were evaluated for confluence by monitoring of transepithelial electric resistance (TEER) during the whole cell growth phase and by inspection with a confocal laser scanning microscope. Electrophysiological measurements were made on cell monolayers mounted in Ussing chambers. The tissue parameters potential difference (dP0), current (I-C), and short-circuit current (I-SC), as well as TEER, were recorded. There was no significant influence of transport direction (apical-basolateral or basolateral-apical) on cadmium absorption. Exposure of Caco-2 cells to different cadmium concentrations resulted in a reduction of cadmium accumulation in Caco-2 cells from 38% (at 1 muM Cd) to 13% (at 10 muM Cd). At all cadmium concentrations (except 5 muM), the actual cadmium transport was approximately 5%. Time course of cadmium accumulation showed an initial rapid phase followed by a phase of slow cadmium accumulation. Transport from inner cell to receiving side took place at a constant speed. Exposure of Caco-2 cells to high doses of cadmium (>100 muM) resulted in a reduced TEER. It can be concluded that a combination of Caco-2 cell model and Ussing chamber system represents an appropriate model for simulation of cadmium absorption and probably for investigations of transport processes of other heavy metals.