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Functional characterization & physiology of NBCe1 from a marine teleost
Author(s) -
Chang MinHwang,
Babcock Gerald T.,
Hirose Shigehisa,
Romero Michael F.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a1233-b
Marine fish are in constant danger of dehydration from osmotic water loss via the gills living in a high‐salt environment. To restore body water, they drink sea water, but must eliminate excess salt. However, the teleost kidney cannot produce urine more concentrated than blood. The gills and intestine therefore eliminate excess Na + , Cl − and HCO 3 − by active salt transport across gill and gut epithelia. Euryhaline Fugu (Takifugu.obscurus, pufferfish) form a “white‐cake” (CaCO 3 ) precipitate on the luminal gut surface after moving from fresh to sea water. We hypothesized that the Na + /HCO 3 − cotransporter (NBCe1) from marine teleosts would have different Na + affinities than human/fresh‐water NBCe1 orthologs. Using T. obscurus , we made a subtraction gut library to see which transporter mRNAs increased in sea‐water. NBCe1 was identified. We subcloned Fugu ‐NBCe1 (fNBCe1) into a Xenopus expression vector and assayed its activity in oocytes. Our experiments revealed (1) fNBCe1 is an electrogenic Na + /HCO 3 − cotransporter; (2) fNBCe1 has lower Na + affinity, yet higher transport capacity/turnover than hkNBCe1. (3) fNBCe1 steady‐state current and IV relationships differ after Na + manipulation than those of hkNBCe1. These results imply that the fNBCe1 and hkNBCe1 Na + affinities differ significantly. Our results with human S427L‐hkNBCe1 mutation indicate that HCO 3 − affinity & Na + handling are associated with TM1. We have made and expressed 3 fNBCe1/hkNBCe1 chimeras which maintain or exchange TM1‐TM5 region. These TM chimeras will allow us to define the TM area(s) important for Na + “binding”/transport. DK56218, AHA.