Interspecies differences in P-glycoprotein mediated activity of multixenobiotic resistance mechanism in several marine and freshwater invertebrates

The presence and function of the P-glycoprotein mediated multixenobiotic re sistance (MXR) mechanism was demonstrated in numerous aquatic organisms. Th e aim of this study was to investigate whether in aquatic organisms exists the inherent, species-specific basal level of MXR activity. Here the result s of the direct comparison of the basal (noninduced) level of MXR activity measured in several marine (Mytilus galloprovincinlis, Monodonta turbinata, Patella lusitanica) and freshwater (Dreissena polymorpha, Viviparus vivipa rus, Anodonta cygnea) molluscs species are presented. The primary criterion for the assessment and quantification of the basal level of MXR activity w as the ratio (R) between the accumulation or efflux of the fluorescent mode l MXR substrates (rhodamine B or rhodamine 123) in or from the gills, measu red with and in the absence of model MXR inhibitors verapamil or cyclospori n A. Significantly different levels of MXR activity were found ill the spec ies investigated. These levels generally show a relatively good correlation with the level of pollution present in their natural habitats. Considering these results a conclusion was reached that in aquatic organisms indeed ex ist the different inherent, species-specific levels of MXR activity. The id entified levels might be, at least paltry, responsible either for the resis tance to, or for the sensitivity of a particular species to organic polluti on. (C) 2000 Elsevier Science Inc. All rights reserved.