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IRBIT binds to and functionally enhances the electroneutral Na + ‐coupled bicarbonate transporters NBCn1, NDCBE and NCBE
Author(s) -
Parker Mark Daniel,
Skelton LaraAnne,
Daly Christopher M,
Boron Walter
Publication year - 2007
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.21.6.a1285-a
Subject(s) - transporter , chemistry , immunoprecipitation , cytoplasm , cotransporter , microbiology and biotechnology , biophysics , hek 293 cells , biochemistry , biology , receptor , gene , organic chemistry , sodium
IRBIT—a soluble protein released from the IP 3 receptor by IP 3 —binds to and functionally enhances the electrogenic Na/HCO 3 cotransporter NBCe1‐B (Shirakabe et al ., PNAS, 103, 2006), a member of the SLC4 family of HCO 3 transporters. Sequence comparisons led us to suspect that IRBIT might also interact with a region in the cytoplasmic N terminus of the electroneutral Na‐coupled HCO 3 transporters NBCn1, NDCBE, and NCBE, all of which play an important role in regulating neuronal pH i . Using an anti‐IRBIT antibody we were able to co‐immunoprecipitate all four transporters‐as well as the brain specific variant NBCe1‐C‐from mouse brain lysate, suggesting an in vivo association. We individually expressed NBCn1, NDCBE, or NCBE with a C‐terminal EGFP tag (collectively described as NBCnX‐EGFP) ± IRBIT with an N‐terminal HA‐tag (HA‐IRBIT) in Xenopus oocytes. While exposing cells to a CO 2 /HCO 3 solution, we monitored the rate of pH i recovery from the CO 2 ‐induced acid‐load using pH‐sensitive microelectrodes. For each NBCnX‐EGFP, co‐expressing HA‐IRBIT doubled the pH i ‐recovery rate. In addition, HA‐IRBIT also doubled the magnitude of the Na conductance associated with NBCn1—evidence that the conductance is intrinsic to the transporter. Our data show that IRBIT is capable of enhancing the activities of all three known electroneutral Na + ‐coupled HCO 3 transporters.