Induction of metallothionein synthesis in rainbow trout,Salmo gairdneri, during long-term exposure to waterborne cadmium

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Abstract
Rainbow trout were exposed to 200 μg cadmium/l in the water during four months at 6–10°C. The liver, kidney and gills were analyzed for cadmium, copper, zinc, metallothionein and metallothionein mRNA. Cadmium accumulated in all three organs and reached the highest concentration in the kidney. The tissue zine and copper concentrations showed no major alterations during the experiment. The cytosolic distribution of cadmium, copper and zinc was followed during four months of exposure by Sephadex G-75 chromatography. It was found that cadmium was predominantly associated with proteins of an apparent molecular vieght of 10,000 daltons. These proteins were further identified as metallothioneins after fast protein liquid chromatography on a Mono-Q column. The metallothionein concentration was significantly higher in liver of exposed fish than in control fish after only one month. The kidneys reached significantly elevated levels of metallothionein in the exposed group after three months. In the gills, elevated metallothionein concentrations were observed after four months of exposure. After four months of exposure, the metallothionein mRNA content of liver and kidney was analyzed using a rainbow trout anti-sense RNA probe. Elevated MT mRNA levels were observed in both kidney and liver. These results demonstrate thatde novo synthesis of metallothionein is induced by cadmium in rainbow trout after exposure to the metalvia water.