Metallothionein synthesis and mRNA levels in cultured hepatocytes from lethal milk mutant mice.

Primary hepatocyte cultures from adult lethal milk (lm) mutant mice displayed approximately a 2.5-fold increased metallothionein (MT) synthesis compared to wild-type cells in uninduced as well as zinc-treated cells, over a 0- to 160-microM zinc dose-response range. Mutant hepatocytes also exhibited a greater level of MT-1 mRNA in both untreated and zinc-treated cultures compared to wild-type. Despite these measures of MT synthesis, untreated lm/lm hepatocytes exhibited twofold-reduced 6-h uptake of 65Zn compared to wild-type, zinc and copper levels in soluble fractions of lm/lm hepatocytes were equivalent to wild-type levels and lm/lm hepatocytes showed increased susceptibility to zinc toxicity as measured by zinc-induced detachment of cells from the culture dishes. These results suggest that the elevated MT synthesis observed in lethal milk mice does not, as previously reported in wild-type hepatocytes (1-3), increase zinc uptake or protect against heavy-metal toxicity (4, 5). Taken together with studies in vivo, our results suggest that an alteration in MT synthesis is probably a secondary affect of the lethal milk mutation.