Tri-n-Butyltin Affects Lipid and Protein Interactions in Mussel Gill Mitochondrial Membranes

Organotins, due to their past widespread use as biocides in antifouling paints, are widely diffused organic pollutants in the aquatic environment. Filter-feeding molluscs efficiently concentrate these xenobiotics in their tissues and metabolize them scarcely. Because of their strong lipophilicity, organotins easily interact with cellular membranes, producing serious toxic effects, especially on mitochondria. In this work, the Tri-n-Butyltin (TBT) in vivo influence on fatty acid composition, on Mg-ATPase activity and on membrane physico-chemical state has been investigated in gill mitochondrial membranes of the bivalve mollusc Mytilus galloprovincialis, an organism largely used in human diet. Experiments were carried out in a confined environment, by exposing animals to 0.5 and 1.0 μg/L TBT doses for 24 and 120 hours. After the exposure time of 120 hours, the higher TBT dose induced a decrease in the total and n-3 polyunsaturated fatty acids, especially 22:6 n-3, and an activation of the hydrolytic capability of the oligomycin-sensitive Mg-ATPase, the enzymatic core of energy production and a well recognized triorganotin target. Laurdan steady-state fluorescence spectroscopy have been used to detect membrane physico-chemical perturbations around the fluorescent moiety, such as a decreased mitochondrial membrane polarity, for both TBT concentrations and the exposure time of 120 hours. Our findings are consistent with the TBT incorporation into the gill mitochondrial membrane and the consequent perturbation of the microenvironmental lipids, well known to modulate the activity of membrane-bound enzymes. The increased functionality of the mitochondrial enzymatic complex could affect energy saving mechanisms and mediate some of the toxic effects.