The effect of copper on ion content (Na+, K+, Ca2+, and Cl−) was evaluated in isolated mantle gills of the marine clam Mesodesma mactroides. Clams were collected at the Mar Grosso Beach (São José do Norte, Rio Grande do Sul [RS], southern Brazil), cryoanesthetized, and had their mantles dissected. Mantle cells were isolated and incubated in a calcium-free phosphate solution without (control) or with Cu (CuCl2). Cells were exposed to Cu for 1 h (5 µM) or 3 h (2.5 and 5 µM). In cells incubated with 2.5 µM Cu, a significant decrease in intracellular Cl− content was observed. However, in cells incubated with 5.0 µM Cu, significant reductions in Na+, K+, and Cl− intracellular content were observed. Given the mechanisms involved in ion transport in mantle cells of the marine clam M. mactroides, the findings described here suggest that Cu exposure inhibits carbonic anhydrase and Na+/K+-ATPase activity. Also, it can be suggested that Cu is competing with Na+ for the same mechanisms of ion transport in the cell membrane, such as the Na+ channels and the Na+/K+/2Cl− cotransporter. Results from the present study also clearly indicate that processes involved in cellular anion regulation are more sensitive to Cu exposure than those associated with the cellular cation regulation. Characterization of sites for Cu accumulation and toxicity in aquatic animals is important for derivation of metal binding constants at the biotic ligand. Also, identification of the mechanism of metal toxicity is needed for modeling metal accumulation in the biotic ligand and its consequent toxicity. Therefore, the findings reported here are extremely valuable for the development of a biotic ligand model version for marine and estuarine waters. Environ. Toxicol. Chem. 2011; 30:1582–1585. © 2011 SETAC
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