Uptake of cadmium and metallothionein by rat everted intestinal sacs

The gastrointestinal uptake and transport of cadmium (Cd) and the role of metallothionein (MT) were studied in everted sacs of rat intestine (ESRI). When ESRI were incubated for 30 min in a medium containing various Cd concentrations (1-5 x 10(-4) M) as CdCl2, Cd-cysteine (Cd-Cyst) or rat liver Cd-MT-II (Cd-MT), a dose-dependent tissue uptake of Cd was observed. In ESRI incubated with Cd-MT, total Cd uptake was lower than that of CdCl2 (25% of CdCl2). Fractionation of the tissue showed that about 80% of Cd in the tissue was recovered in the particulate fraction after CdCl2 and Cd-Cyst incubation, while that after Cd-MT incubation was present mainly in the cytosol fraction (about 80%). Most of the Cd in the cytosol fraction of Cd-MT-incubated ESRI was associated with a 10,000 molecular weight protein on Sephadex G-75 column fractionation. Similar results were obtained after incubation of ESRI from Zn-pretreated rats with 109CdCl2 solution. In addition to the Cd-MT peak, there was a small peak of Cd associated with a high molecular weight fraction. Only a small percentage of Cd was leaked to serosal fluid in the everted sacs incubated at a low concentration of CdCl2 (0.8%) but this leakage of cadmium was increased at higher concentration and was higher after incubation with Cd-MT. The results suggest that the uptake of Cd from CdCl2 and Cd-MT is different. Although Cd-MT was taken up intact by everted sacs, the uptake was slow as compared to Cd salts. The intracellular presence of MT had little effect on the uptake of CdCl2 but the Cd was sequestered by MT in the intestine.