Functional characterization of four aquaporins (AQPs) cloned from the European eel, Anguilla anguilla

The eel is a euryhaline teleost which exhibits remarkable adaptation in moving between fresh (FW) and sea water (SW) environments. We are investigating how the eel osmoregulates by functionally characterizing four eel aquaporins (AQP1, AQP1dup [a gene duplication of AQP1], AQP3 and AQPe [possibly an AQP10 homolog]) using the Xenopus oocyte expression system. Water fluxes were measured by exposing oocytes to hypotonic solutions and quantitating cross‐sectional area. Urea and glycerol fluxes were measured by isotope uptake. AQP1, expressed in intestine (up in SW), oesophagus and kidney (down in SW) showed high Hg 2+ ‐inhibitable water fluxes, but no urea or glycerol transport. AQP1dup found in the same tissues but with high variability in expression, exhibited the same transport specificities but water permeability was ~50% of AQP1. AQP3 in the gill is dramatically downregulated in SW and exhibited high water, urea and glycerol permeabilities. These permeabilities were >90% inhibited at pH6.5. None of the other AQPs were inhibited by pH. AQPe was also an aquaglyceroporin which could transport glycerol and urea as well as water at high rates. It is found in intestine and kidney and exhibits little change in SW or FW. Eel AQPs have similar transport specificities to their human orthologs but are uniquely regulated by environmental salinity. This work supported by a New Investigator Award from the MDIBL and NIH DK43955