Inhibition of multixenobiotic resistance mechanism in aquatic organisms: ecotoxic consequences

Recent evidence indicates that inherent presence of multixenobiotic resistance (MXR) mechanism in sponges, mussel and fish represents a general biological defence mechanism for their protection against both endogenous and environmental toxins. In aquatic organisms exposed to polluted waters, this P170 glycoprotein pump removes out of cells also ‘new’, man-made toxic chemicals. Many chemical agents, the ‘chemosensitizers’, may alter the function of this fragile mechanism. The knowledge that the presence of one xenobiotic may block the pumping out of other xenobiotic(s), and hence accelerate their accumulation, may have important implications on environmental parameters like exposure, uptake, bioaccumulation, and toxicity. In this report we present the results of measurements of MXR-phenotype expression using the ‘accumulation’ technique and the modulators of MXR, verapamil and staurosporine, demonstrating (1) the interpopulation differences in the level of MXR expression in a marine snail Monodonta turbinata and its induction in specimens exposed to polluted waters, (2) the characteristics of the MXR-expression in a mussel Mytilus galloprovincialis, and (3) how model- or natural-inhibitors of MXR can modulate the no observed effect concentrations (NOEC) of xenobiotics in a fresh water clam Corbicula fluminea and a carp Cyprinus carpio to the observed effect concentrations (OEC).