Analysis of the detoxification of heavy metal ions by mouse metallothionein.

A mouse hepatoma cell line selected for resistance to Cd (Cdr 80 hepa) was compared to the unselected parental hepatoma cell line (Cds hepa) in terms of its sensitivity to a variety of metal ions. The Cdr 80 hepa cells have double minute chromosomes which carry amplified copies of the MT-I and MT-II genes and can accumulate approximately 20-fold more MT mRNA than Cds hepa cells when stimulated with an optimal dose of Cd. The metals Zn, Cu, Ag, Hg, Co, Ni, and Bi also induce higher levels of MT mRNA in the resistant cells than in the unselected cells, yet the Cdr 80 hepa cells only show increased resistance to the toxic effects of Zn, Cu, Hg, and Bi. These results indicate that not all metals which induce MT mRNA are detoxified by the protein.