HEAVY-METAL INTRACELLULAR BALANCE AND RELATIONSHIP WITH METALLOTHIONEIN INDUCTION IN THE LIVER OF CARP AFTER CONTAMINATION BY SILVER, CADMIUM AND MERCURY FOLLOWING OR NOT PRETREATMENT BY ZINC

Determination of metal levels (copper, zinc, cadmium, silver and mercu ry) in soluble and insoluble fractions of liver homogenates has been p erformed after 7 days exposure of carps (Cyprinus carpio) to moderate concentrations of cadmium, silver and mercury in water. Metallothionei n (MT) levels have been quantified by a polarographic method before an d after the contamination and a subsequent decontamination phase (7 da ys). The influence of pretreatment by zinc (7 days) has also been eval uated. MT level variations have been interpreted as having regard to i nter-related flows of metal between subcellular fractions. Special int erest has been focused on heat-stable compound (HSC)-bound heavy metal flows within the cytosol, taking in account that MT is the major comp onent of these ligands. Our data showed differences between the abilit y of metals to bind cytosolic ligands and HSCs, and their respective p otency for MT induction in liver. Regardless of pretreatment, mercury gave the highest increase of liver MT, but the MT level decreased duri ng the decontamination step, especially after pretreatment by zinc. Ca dmium and silver gave similar increases, but a significant difference with the control appeared only after the decontamination step with cad mium, while 1 week of contamintion was enough for silver. However, sil ver binding with MT was achieved only by the end of the decontaminatio n step, while cadmium depicted the highest ratio for HSC-bound toxic m etals after the contamination. Our experimental conditions gave the fo llowing order of potency for MT induction in liver: mercury much great er than silver > cadmium > zinc. Results are discussed comparatively w ith data obtained with carp gills.