Dynamics of (Cd,Zn)-metallothioneins in gills, liver and kidney of common carp Cyprinus carpio during cadmium exposure.
Résumé
Cadmium concns., (Cd,Zn)-metallothionein (MT) concns., MT synthesis, and the relative amts. of cadmium bound to (Cd,Zn)-MTs were detd. in gills, liver, and kidney of common carp C. carpio exposed to 0, 0.5 μM (0.06 mg·L-1), 2.5 μM (0.28 mg·L-1), and 7 μM (0.79 mg·L-1) Cd for up to 29 days. Cadmium accumulation was in the order kidney\textgreaterliver\textgreatergills. Control levels of hepatic (Cd,Zn)-MT were 4 times higher compared to those of gills and kidney. No increases in (Cd,Zn)-MT concns. were obsd. in the liver during the exposure period. In comparison with control carp, (Cd,Zn)-MT concns. increased up to 4.5 times in kidney and 2 times in gills. In both these organs, (Cd,Zn)-MT concns. were linearly related with cadmium tissue levels and with the de novo synthesis of MTs. Hepatic cadmium was almost completely bound to (Cd,Zn)-MT, while percentages of non-MT-bound cadmium were at least 40% in gills and 25% in kidney. This corresponded with a total satn. of (Cd,Zn)-MT by cadmium in kidney and a satn. of ∼50 and 60% in gills and liver, resp. The final order of non-MT-bound cadmium was kidney\textgreatergills\textgreaterliver. The results indicate that cadmium exposure causes toxic effects, which cannot be correlated with the accumulated levels of the metal in tissues. Although cadmium clearly leads to the de novo synthesis of MT and higher (Cd,Zn)-MT concns., the role of this protein in the detoxification process is clearly organ-specific and its synthesis does not keep track with cadmium accumulation. [on SciFinder(R)]