EVIDENCE FOR A MULTIXENOBIOTIC RESISTANCE MECHANISM IN THE MUSSEL MYTILUS-GALLOPROVINCIALIS

Membrane vesicles isolated from the gills, mantle, and digestive gland of the marine mussel Mytilus galloprovincialis possess a potential similar to that involved in multidrug resistance (MDR) described in resistant tumor cell lines: they bind 2-acetylaminofluorene (AAF) in saturable and trypsin- and verapamil-sensitive manner. Cytosolic fractions from mussel tissue homogenates reveal a relatively high glutathione-S-transferase (GST) and glutathione-peroxidase (GSH-Px) activities with substrate affinities similar to the isoenzyme of anionic GST and its intrinsic GSH-Px involved in MDR. In mussel these biochemical elements of the MDR mechanism seem to be inherent, rather than induced, since they were found in specimens living in the pristine aquarium of Limski Kanal, Northern Adriatic. The enhancement in the accumulation of AAF in laboratory exposure experiments in the presence of verapamil indicates that the MDR-like mechanism functions in mussel also in vivo. The recognition that the MDR-like mechanism is operative in mussel may explain the relative resistance of this species to pollution. The knowledge that the presence of one xenobiotic may block the pumping out, and hence accelerating accumulation, of other(s), may help us to understand and interpret our present and past data on different parameters obtained with this most exploited indicator organism.