The localization of mercury and metallothionein in the cerebellum of rats experimentally exposed to methylmercury.

Rats were dosed with methylmercuric chloride, either by gastric gavage (5 x 10 mg kg-1 body weight over a 15-day period), or in their drinking water (20 mg methylmercuric chloride l-1 for 14 or 42 days). Localization of mercury within the cerebellum was performed with a silver physical development technique, and metallothionein with dinitrophenyl hapten-sandwich immunohistochemistry. Mercury was detected in structurally undamaged Purkinje neurones and adjacent Bergmann glial cells; no mercury was detected in granule cells even though these small cells nearest the Purkinje layer had a high incidence of pyknotic nuclei. In general, metallothionein was detected mainly in Bergmann glial cells, Purkinje cells, astrocytes and glial cells of white matter; no metallothionein was detected in granule cells. We hypothesized that the resistance of Purkinje cells to methylmercuric chloride reflects their ability to transform organic mercurials to inorganic mercury that, in turn, induces the synthesis of radical-scavenging metallothionein molecules.

The ultrastructural localization of metallothionein in cadmium exposed rat liver.

The ultrastructural localization of metallothionein (MT) was investigated in the liver of male Wistar rats by a cryo-immunocytochemical technique. The liver parenchymal and sinusoidal cells were studied in both cadmium-exposed (3 x 1.2 mg kg-1 as cadmium chloride) and non-treated animals. Treatment with cadmium induced the synthesis of MT yet differences in the distribution were evident amongst the various types of liver cell. MT was found most abundantly in the parenchymal and endothelial cells, yet was absent in the stellate cell and sparsely distributed in the Kupffer cell. In the cells where MT gene expression was induced, the metalloprotein was distributed within both the nuclear and cytoplasmic compartments. The significance of the nuclear localization of MT is discussed.

Metallothionein: a protein conferring resistance in vitro to tumor necrosis factor.

The role of metallothionein (MT) in the cytotoxicity of tumor necrosis factor (TNF) was investigated in vitro. A human epithelial cell line (HE100) and a mouse fibroblast line (CI 1D100) had previously been cultured to become resistant to 100 microns CdCl2 and were cultured routinely in cadmium-containing medium. The MT content of these cells and the nonresistant parent cell lines (HE and CI 1D) was determined both qualitatively and quantitatively by immunochemical techniques. Immunofluorescence microscopy revealed the cadmium-resistant cell lines to be intensely rich in MT in both the nuclear and cytoplasmic compartments. This finding was confirmed by immuno-electron microscopy which also showed the labeling to be freely distributed and not membrane-bound. In comparison, a very weak labeling of the parent cell lines was observed. MT concentration, as determined by enzyme-linked immunosorbant assay, was found to be 4.05 +/- 1.13% and 3.91 +/- 0.7% of the total protein for HE100 and CI 1D100 cells, respectively. We were unable to detect MT in the parent cell lines by this technique. Dose-survival curves obtained after 3 days treatment of the cells with TNF (0.125-500 ng/ml) revealed that the MT-rich substrains were significantly resistant compared to the parent strains (P < 0.001; t tests). In growth rate studies, where cells were exposed to TNF over a dose range of 0.25-250 ng/ml for 6 days, the resistance of the MT-rich cell lines was confirmed (P < 0.002). These data indicate that MT confers resistance to the cytotoxic effects of TNF in vitro and that sensitivity to TNF may be related to the MT content of the cell.