Heavy metals and glutathione metabolism in mussel tissues

Data are presented on the tissue glutathione content and on the activity of two of the main enzymes involved in GSH metabolism (gamma-glutamyl-cystein e synthetase (GCS), GSH transferase (GST)) in the gills and digestive gland of mussels (Mytilus galloprovincialis Lam.) exposed for 1, 4 and 7 days to sublethal concentrations of copper and of mercury, both in the inorganic f orm of HgCl2 and in the organic form of CH3HgCl. The results indicate that Cu2+. (0.6 mu M) and CH3Hg+ (0.2 mu M) can affect, although to a different extent, glutathione metabolism in mussel tissues; common traits were a decr ease in tissue glutathione content, stimulation of GST activity and inhibit ion of GSH synthesis rate; on the other hand, inorganic Hg2+ (0.2 mu M) did not significantly affect glutathione content and metabolism in mussel tiss ues. Exposure to copper (0.6 mu M) resulted in a decrease in total glutathi one content in both gills and the digestive gland that was maximal after th e first day, followed by a tendency to recover at longer exposure times. Su ch a decrease seemed to be mainly related to a stimulation of GST activity, which was transient in gills and persistent in the digestive gland. The ti ssue glutathione content was also decreased in mussel exposed to methylmerc ury (0.2 mu M); however, such a decrease seemed to be mainly due to inhibit ion of the GSH synthesis rate and, to a (0.2 mu M) did not significantly af fect lesser extent, to an increased GST activity. On the contrary, inorgani c Hg2+ (0.2 mu M) did not significantly affect glutathione metabolism, alth ough mussel exposure to the same concentration of organic and inorganic Hg2 + resulted in similar total metal tissue load in mussel tissues. The role o f glutathione as a potential defense against heavy metals is discussed in r elation to different routes of metal toxicity and homeostasis in mussel tis sues. (C) 1999 Elsevier Science B.V. All rights reserved.