Cadmium uptake and metabolism in cultured cells

Cultured cells have been made resistant to otherwise lethal concentrations of the toxic Cd ion, probably by induction of metallothionein (MT) synthesis and binding of Cd to the MT. One human epithelial cell line (HE) and two enzyme-deficient mutants of mouse fibroblasts (L-cells) (Cl 1D and A9) and their Cd-resistant substrains with a high content of MT, have been used to study cellular Cd uptake and metabolism. For cell survival of "wild type" cells, the critical level of intracellular Cd is determined to be around 6 nmole Cd/mg cell protein. Resistant cells can tolerate Cd levels several times above this concentration, if the major part of Cd is bound to MT. The technique of perturbed angular correlation spectroscopy (PAC) has been applied to living Cd-resistant cells. It was shown that greater than 66% of Cd in the resistant strains was bound to MT, and that MT is apparently freely suspended in the cell cytoplasm. Chelating agents differ in toxicity and Cd-releasing effect on the cells, but apparently remove the non-MT-bound Cd pool. After various periods of Cd omission, either in vitro or in vivo, growing the cells as tumors in athymic nude mice, the stability of Cd resistance in these cells seems to be dependent on the capacity of cells for de novo synthesis of MT shortly after re-exposure to the metal.