Distribution and retention of mercury in metallothionen-null mice after exposure to mercury vapor

We studied the role of metallothionein (MT) in the distribution and retention of mercury in the brain, lung, liver and kidney of MT-null and wild-type mice after exposure to mercury (Hg0) vapor. Mice were exposed to Hg0 vapor at 5.5-6.7 mg/m3 for 3 h and killed at 1, 24, 72 or 168 h after exposure. One hour after exposure to Hg0 vapor, there were no differences in mercury concentrations in these organs from MT-null and wild-type mice. However, the elimination rate of mercury from the organs, except the brain, were remarkably faster in MT-null mice than in wild-type mice. MT-I and -II levels in the lung and kidney were increased significantly in wild-type mice but not in MT-null mice at 24 h after exposure to Hg0 vapor. At this time point, over 65% of the mercury was retained in the MT fraction of the cytosol of organs from wild-type mice. In contrast, mercury appeared mainly in the high-molecular-weight protein fractions in the cytosol of organs from MT-null mice. In the brain, a large amount of mercury was bound to MT in both strains of mice immediately after exposure. No difference was observed in the elimination rate of mercury from the brain between both strains of mice. Brain MT levels were elevated slightly in wild-type mice at 168 h after exposure but could not be detected in MT-null mice. These data suggest that no detectable MT-I and -II levels were found in the brain of MT-null mice and that mercury was apparently bound to MT-III. Using MT-null mice, we showed also that MT-III may play an important role in the retention of mercury in the brain.