Localization of renal Cu-binding metallothionein induced by Au injection into rats

The localization of Au-induced metallothionein (MT) in kidneys is reported. Au, Cu and Zn contents in kidneys and liver increased after Au injection. Especially the Cu content in the kidney increased in comparison with the Zn content. The yellow-orange autofluorescent signals which are a marker of Cu-MT were observed predominantly in the outer stripe of the outer medulla with a ring shape in the kidneys of Au-injected rats. MT mRNA was also located in only the outer stripe of the outer medulla. Neither autofluorescence nor MT mRNA was found in the kidneys of control rats. These results indicate that MT was biosynthesized in only the outer stripe of the outer medulla and the biosynthesized MT was bound to Cu. Representative Sephadex G-75 elution profiles of the renal cytosol of rats injected with Au showed that Au, Cu and Zn contents in MT fractions increased after Au injection. Interestingly, Cu in MT fractions dramatically increased in comparison with Zn in the MT fractions in spite of Au injection into rats. Only the Cu-containing MT fractions emitted a yellow-orange autofluorescence. The accumulated Cu in the kidneys of Au-injected rat was thought to be associated with renal toxicity.