The European Eel (Anguilla Anguilla) is a euryhaline teleost, which can survive in a wide range of salinities. During adaptation to a saltwater environment there are changes in the expression levels of a number of aquaporin water channels, including eAQP1 and eAQP3 (Lignot et al., 2002; Martinez et al., 2005). Recently we demonstrated that eAQP3 has a limited permeability to H₂O, but causes significant increases in both urea and methylammonium uptake (Walton et al., 2008). Over the last 30 years there have been dramatic falls in worldwide populations of eels. This decrease in eel population coincides with an increase in the levels of environmental brominated flame-retardants (BFRs). In the current study we investigated the effect of the BFR pentabromophenylether (PDBE) on the function of eAQP3. eAQP3 was subcloned into the eGFP expression plasmid pEGFP-C2. MDCK II cells were grown on permeable filters and transiently transfected with 1µg of cDNA encoding either eGFP-AQP3 or the eGFP control plasmid. To determine the cellular localization of eAQP3 the cells were fixed and viewed using confocal microscopy. Urea uptake experiments were performed on single monolayers. The cells were exposed to an uptake solution (in mM, Mannitol 280, Urea 1, CaCl₂ 1.8, MgCl₂, 1, KCl 2, HEPES 5, pH7.4 supplemented with 2µCi/ml ¹⁴C-Urea) for 90s, followed by several washes in an ice-cold stop solution (in mM Mannitol, 270, Urea 10, CaCl₂ 1.8, MgCl₂ 1, KCl 2, HEPES 5, pH 7.4). The cells were dissolved in 10% SDS and ¹⁴C-urea measured by scintillation counting. All uptake values are quoted as mean ± SEM and the units are pMol urea.cm².90s^-1. Statistical analysis has been performed using paired or unpaired t-tests as appropriate and significance is assumed at the 5% level. PDBE was prepared as a 1mM stock in DMSO. When expressed in MDCK cells, eAQP3 was delivered to both the apical and basolateral membranes. In monolayers transiently transfected with eGFP-eAQP3 there was a significant increase in urea uptake compared to monolayers transfected with the control plasmid (eAQP3, 973.0±229.3; control 537.8±223.9 p=0.01, n=3). A 1hr incubation in 1µM PDBE caused a significant reduction in urea uptake in eAQP3 expressing cells (eAQP3, 1276.0 ± 224.3, n=8; eAQP3 + PDBE, 630.8 ± 79.5, n=8, p=0.02) but was without effect on control cells (eGFP, 379.4 ± 48.3, n=8; eGFP + PDBE, 302.1 ± 48.1, n=8, p=0.28). In addition we found that treatment with PDBE caused a redistribution of eGFP-eAQP3 fluorescence from the cell membrane into a cytoplasmic compartment. In summary we have shown that eGFP-tagging at the N-terminal does not the affect the ability of the eAQP3 to transport urea. In addition exposure to PDBE inhibits eAQP3. This effect of PDBE is most likely due to an internalization of eAQP3.