title: Differential role of metallothionein on Zn, Cd and Cu accumulation in hepatic cytosol of rats.
abstract: To examine the role of metallothionein (MT) on heavy metal accumulation in hepatic cytosol of rats, this study was carried out to determine the relative Zn, Cd and Cu-binding capacities of MT in hepatic cytosol of Zn, Cd and Cu-injected rats, respectively. The heavy metal contents were detected in the liver and cytosol in the following proportions: 65.2-74.8% of the Zn content, 61.9-65.6% of the Cu content, and approx. 65% of the Cd content. Each rat was given a single intraperitoneal injection of saline, ZnSO4 (1, 5, 10 and 20 mg Zn/kg b.w.), CuSO4 (2, 4 and 6 mg Cu/kg b.w.) or CdCl2 (1, 2 and 3 mg Cd/kg b.w.). The amounts of the increased Zn and Cu were attributable to MT and high molecular weight proteins, while most of the increased Cd was attributable to MT. There was a close relationship between heavy metal content of the cytosol and MT in all heavy metal-injected rats. Our data demonstrated that approx. 60% of the increased Zn or Cu in the hepatic cytosol of Zn or Cu-injected rats was bound to MT, while 83% of the increased Cd in hepatic cytosol of Cd-injected rats was bound to MT. Therefore the order of relative binding capacity in vivo of MT determined for several metals (Cd > Zn > Cu) did not correlate with the published in vitro order of affinity to MT, Cu > Cd > Zn. These results suggested that the role of MT in Zn or Cu accumulation in the liver of Zn or Cu-injected rats was different from that of MT in Cd accumulation in the liver of Cd-injected rats.
authors.affiliation: Department of Environmental Medicine and Informatics, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Saito
authors.forename: Y
authors.initials: Y
authors.lastname: Kojima
mesh_terms: D000818:Animals; D002104:Cadmium / Q000378:metabolism*; D003300:Copper / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D008668:Metallothionein / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015032:Zinc / Q000378:metabolism*
chemical_list: D002104:Cadmium; D003300:Copper; D008668:Metallothionein; D015032:Zinc