A coordinated system of transport proteins, channels, receptors and enzymes act as cellular gatekeepers to foreign molecules, critically determining the so-called ADME-Tox (absorption, distribution, metabolism, excretion – toxicity) properties of a molecule. The polyspecific uptake and efflux transmembrane proteins are essential components of this complex cellular defense and detoxification/xenobiotic processing machinery in mammals, highly important and widely recognized in the context of pharmacology and human toxicology. However, they are scarcely investigated in non-mammalian species, and not adequately addressed in the field of environmental toxicology. Consequently, the major goal of the proposed project is identification and detailed functional characterization of new, potentially (eco)toxicologically relevant uptake and efflux transport proteins not addressed so far in the context of environmental toxicology, or in non-mammalian species in general. Our research will be focused on selected polyspecific uptake transport proteins from the SLC21 and SLC22 (Solute Carriers) proteins families, the efflux transporters from the MATE (multidrug and toxic compound extrusion proteins) family, and finally the RLIP76 as the most recently discovered stress-responsive, multi-functional membrane protein. We will use zebrafish (Danio rerio) as a highly relevant vertebrate research model, and our methodological approach will be based on several subsequent research phases: phylogenetic and gene expression analyses; transfection studies in appropriate heterologous expression system(s); transport-activity assays; analyses of the transport mechanism and structural properties; high-throughput-screening identification of chemical interactors of selected transporters among environmental contaminants; and finally in vivo evaluation of the (eco)toxicological relevance of selected transporters using the zebrafish functional genomics tools.