The activity of multixenobiotic resistance mechanism determined by rhodamine B-efflux method as a biomarker of exposure

An important characteristic of multixenobiotic resistance (MXR) is its inducibility. The level of MXR-expression in field populations of aquatic organisms is directly proportional to the level of pollution. This property offered the possibility to use the MXR-activity as a biomarker of exposure. However, before application of MXR-activity as a relevant biomarker, direct demonstration of the dynamic of MXR-activity response to exposure to xenobiotics, as well as its response to cessation of exposure, are required to make plausible that idea. For these reasons we examined the dynamics of the rate of induction of MXR-activity in marine mussel Mytilus galloprovincialis during either experimental exposure to seawater spiked with 1 μM rhodamine 123 or with Diesel-2 oil (equivalent to 100 ppb of Kuwait oil), or in-the-field exposure to pollution. The rate of deinduction was followed in field-specimens during the recovery period after their transfer from the polluted to the unpolluted site. The level of expression of MXR-transporter in these experiments was assessed by measurement of the rate of accumulation, or the rate of release, of rhodamine B. The induction of MXR-activity was completed within four days, and its deinduction was completed within the same time. However, despite this promptness in response, it remains to explore in future research whether the high natural level of the MXR-activity in combination with a relatively weak rate of induction allows its plausible use as a biomarker of exposure to xenobiotics.