Differential effect of organotins on two Na+-dependent-ATPase activities in Mytilus galloprovincialis.

The widespread occurrence of organotin compounds in the aquatic environment, due to their large use in the past in antifouling paints, still represents a harmful environmental threat, especially in coastal waters, due to their persistency and bioaccomulation. Filter-feeding molluscs efficiently incorporate organotins in their tissues and exhibit a wide range of responses at different levels. As organotin effects on Na-dependent ATPase activities involved in ionic regulation in bivalve molluscs have been quite unexplored by the literature, we investigated the in vitro effect of different organotins on the Na,K-ATPase and the ouabain-insensitive Na-ATPase in cultivated mussels (Mytilus galloprovincialis) from the Adriatic sea. ATPase activities were spectrophotometrically evaluated on gill and mantle microsomal fractions in the presence of increasing concentrations of the contaminants tributyltin (TBT), monobutyltin (MBT), dibutyltin (DBT) and tetraethyltin (TET), as representative of completely apolar organotins, added to the reaction medium immediately before starting the ATPase reaction. While the Na- ATPase showed an overall organotin refractoriness, the Na, K-ATPase, especially in the gills, was confirmed as a possible target of organotins, being progressively inhibited by increasing TBT and DBT concentrations. The effect followed the order TBT > DBT >> MBT = TET (both uneffective). A 20% inhibition of the Na-ATPase activity by DBT in the range 1–40 lMwas surprisingly detected. Organotin effect seem to be related to the polarity of the molecule and to the possible interaction with membrane structures. Moreover, as other contaminants, organotins act differently on the two Na-dependent ATPase activities in bivalve molluscs.