Do selenium and glutathione (GSH) detoxify mercury in marine invertebrates? Effects on lysosomal response in the tropical blood clam Anadara granosa

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Abstract
Interactions of mercury, selenium and glutathione (GSH) with the lysosomal enzymes arylsulphatase and acidphosphatase in the digestive cells of the tropical blood clam Anadara granosa (L.) were studied. After 96 h exposure in vivo, mercury and selenium individually activated arylsulphatase to varying degrees. The latency of the enzyme also increased significantly. On exposure to a combination of mercury and selenium, total and free arylsulphatase activity was inhibited but the increase in lysosomal bound activity was significantly greater. Exposure to GSH alone and in the presence of Hg resulted in considerable decreases in arylsulphatase activity. Hg, Se and GSH, either alone or in combination, had no significant effect on acidphosphatase activity. In vitro inhibition of both arylsulphatase and acidphosphatase depended on concentration of mercury. Selenium inhibited acidphosphatase activity, but not that of arylsulphatase. Both arylsulphatase and acidphosphatase previously inhibited by Hg were completely reactivated and latency restored by GSH. Inhibition and reactivation were dependent upon concentration of Hg and GSH. Bioaccumulation of Hg in soft tissues was increased by about 50% in clams exposed to combination of Hg and Se compared to clams exposed to Hg alone. However, uptake of Hg was completely (95%) blocked by GSH. Thus, clams exposed to Hg, Se and GSH individually and in combination showed different effects on lysosomal enzyme activity in vitro and in vivo. Unlike among vertebrate species, Se failed to provide protection against deleterious effects of Hg in the marine clam. Glutathione, on the other hand, unequivocally provided effective protection.

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