title: Natural organic matter (NOM) has the potential to modify the multixenobiotic resistance (MXR) activity in freshwater amphipods Eulimnogammarus cyaneus and E. verrucosus.
abstract: Based on the chemical features of natural organic matter (NOM) with its variety of functional groups, we hypothesized that NOM will modify the multixenobiotic-resistance (MXR) of an organism as xenobiotic chemicals do. The MXR system is a general first rather non-specific line of defense against environmental contaminants. The aim of this study was to compare the impacts on MXR activity in amphipod species (Eulimnogammarus cyaneus and E. verrucosus, from Lake Baikal) stressed by cadmium chloride or dissolved NOM for 24 h. NOM exposure concentrations were environmentally realistic. MXR activity was assessed based on rhodamine B efflux; its specificity was proven by a verapamil inhibition assay. It was shown that both NOM and CdCl(2) lead to substantial reduction of the rhodamine B efflux. This suggests that NOM may be regarded as a chemosensor which is able to reduce the efficiency of the MXR system. Possible mechanisms of direct NOM impact on MXR processes are discussed, such as peroxidation of the membranes (including P-glycoproteins) or internal blockage of the MXR pump by bioconcentrated NOM. In general, our results show that well-developed depuration pathways of freshwater organisms in contaminated environments may be impaired by strong chemical stressors and, more important, by natural biogeochemical matrices such as humic substances--humic substances are present in all freshwater systems.
authors.affiliation: Irkutsk State University, 664003, Irkutsk, Russia. mtim@irk.ru
authors.forename: M A
authors.initials: MA
authors.lastname: Timofeyev
authors.forename: Z M
authors.initials: ZM
authors.lastname: Shatilina
authors.forename: D S
authors.initials: DS
authors.lastname: Bedulina
authors.forename: R
authors.initials: R
authors.lastname: Menzel
authors.forename: C E W
authors.initials: CE
authors.lastname: Steinberg
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000187:drug effects / Q000378:metabolism; D033304:Amphipoda / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D019256:Cadmium Chloride / Q000633:toxicity; D045424:Complex Mixtures; D018432:Drug Resistance, Multiple / Q000502:physiology*; D004777:Environment; D005618:Fresh Water; D012235:Rhodamines / Q000493:pharmacokinetics; D012800:Siberia; D014700:Verapamil / Q000633:toxicity; D014874:Water Pollutants, Chemical / Q000633:toxicity; D015262:Xenobiotics / Q000633:toxicity
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D045424:Complex Mixtures; D012235:Rhodamines; D014874:Water Pollutants, Chemical; D015262:Xenobiotics; D014700:Verapamil; D019256:Cadmium Chloride; C029773:rhodamine B