Tissue-specific cadmium accumulation and metallothionein-like protein levels during acclimation process in the Chinese crab Eriocheir sinensis.
Aquatic organisms chronically exposed to cadmium can increase their resistance to a subsequent elevated exposure. In order to investigate mechanisms involved in acclimation process in the Chinese crab Eriocheir sinensis, we compared Cd level as well as metallothionein-like protein (MTLP) content in different tissues after direct acute exposure (i.e. 500 microg Cd L(-1) for 3 days), and after acute following chronic (i.e. 10 or 50 microg Cd L(-1) for 30 days) exposure. Cadmium accumulation occurred in the following order: anterior gill>hepatopancreas>posterior gill>carapace>hemolymph>muscle. As high concentrations as 188 microg Cd g(-1) w.w. were reported in anterior gills and seem to reach a saturation level. In these gills, the highest MTLP induction was observed after a direct acute exposure, for which a correlation with Cd content occurred. However, the Cd-binding potential by MTLPs was exceeded for any exposure condition. In hepatopancreas, the highest Cd level was reported for crabs acclimated during 30 days to 50 microg Cd L(-1) before challenging with an acute exposure. Moreover, we showed that MTLPs were induced during the acclimation process. In this organ, MTLPs are theoretically sufficient to bind all Cd. These results suggest that during a chronic exposure to 50 microg Cd L(-1), Chinese crabs acquire the capacity to hold more cadmium in hepatopancreas where it can be sequestrated by MTLPs. On the contrary, MTLP induction seems to be a rapid response to acute exposure in anterior gill, but is not sufficient to sequester all Cd. Other sequestration and/or detoxification mechanisms must take place in anterior gill to cope with high Cd levels.