Subcutaneous NaAs3+ exposure increases metallothionein mRNA and protein expression in juvenile winter flounder

We investigated the effect of NaAs3+ exposure on liver metallothionein (MT) mRNA and protein expression in juvenile winter flounder (Pleuronectes americanus). Sexually immature flounder (age 18 months) were subcutaneously implanted with silastic tubing containing 0 (vector control), 1.5, 3.0, 6.0 and 16.0 mu mol g-1 fish wt. NaAs3+. Liver MT mRNA and protein were significantly elevated within 24 h of exposure at the 1.5 mu mol g-1 dose before there was significant liver As accumulation or mortality. All four NaAs3+ treatments caused a significant rise in MT mRNA and protein and the mRNA demonstrated the clearest dose ressponse and greatest fold change (19 fold at 16.0 mu mol g-1 dose). MT protein reached its maximum (1.8 times the control) at the 1.5 mu mol g-1 dose. This maximum was maintained across all four treatments and decreased slightly at the 16.0 mu mol g-1 dose where there was 40% mortality. The level of liver As content among fish with maximal MT expression was similar to that of fish which recently succumbed to NaAs3+ toxicity.