Cytosolic redistribution and enhanced accumulation of Cu in gill tissue of Littorina littorea as a result of Cd exposure

Metallothionein (MT) binds Cd and Cu with differential affinity. The stability constant of Cu-thioneine is approximately two orders of magnitude greater than that of Cd-thioneine. Thus, it may be expected that MT, induced by Cd exposure, may sequester cytosolic Cu in preference to Cd, resulting in a concomitant redistribution of the metal. In this study, two groups of the marine gastropod, Littorina littorea, were exposed to NTA-buffered seawater solutions, which contained equal free-ion activities of Cu but either low or high Cd free-ion activities. ICP-MS analyses of gill-tissue cytosols show an increase in the concentrations of both Cd and Cu upon exposure to high concentrations of Cd. SE-HPLC profiles indicate that Cd is accumulated in a Cd and Cu metal-binding-ligand pool that may contain MT. Furthermore, a redistribution of Cu to this pool from two low-molecular-weight ligand pools is evident. If these results are reflective of the in-vivo situation and Cu is being sequestered from essential Cu-containing enzymes, then MT induction by Cd intoxication may ultimately result in metal-induced toxicity brought about by cellular Cu deficiency.