title: IRBIT coordinates epithelial fluid and HCO3- secretion by stimulating the transporters pNBC1 and CFTR in the murine pancreatic duct.
abstract: Fluid and HCO3- secretion are vital functions of secretory epithelia. In most epithelia, this entails HCO3- entry at the basolateral membrane, mediated by the Na+-HCO3- cotransporter, pNBC1, and exit at the luminal membrane, mediated by a CFTR-SLC26 transporters complex. Here we report that the protein IRBIT (inositol-1,4,5-trisphosphate [IP3] receptors binding protein released with IP3), a previously identified activator of pNBC1, activates both the basolateral pNBC1 and the luminal CFTR to coordinate fluid and HCO3- secretion by the pancreatic duct. We used video microscopy and ion selective microelectrodes to measure fluid secretion and Cl- and HCO3- concentrations in cultured murine sealed intralobular pancreatic ducts. Short interference RNA-mediated knockdown of IRBIT markedly inhibited ductal pNBC1 and CFTR activities, luminal Cl- absorption and HCO3- secretion, and the associated fluid secretion. Single-channel measurements suggested that IRBIT regulated CFTR by reducing channel mean close time. Furthermore, expression of IRBIT constructs in HEK cells revealed that activation of pNBC1 required only the IRBIT PEST domain, while activation of CFTR required multiple IRBIT domains, suggesting that IRBIT activates these transporters by different mechanisms. These findings define IRBIT as a key coordinator of epithelial fluid and HCO3- secretion and may have implications to all CFTR-expressing epithelia and to cystic fibrosis.
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA.
authors.forename: Dongki
authors.initials: D
authors.lastname: Yang
authors.forename: Nikolay
authors.initials: N
authors.lastname: Shcheynikov
authors.forename: Weizhong
authors.initials: W
authors.lastname: Zeng
authors.forename: Ehud
authors.initials: E
authors.lastname: Ohana
authors.forename: Insuk
authors.initials: I
authors.lastname: So
authors.forename: Hideaki
authors.initials: H
authors.lastname: Ando
authors.forename: Akihiro
authors.initials: A
authors.lastname: Mizutani
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Mikoshiba
authors.forename: Shmuel
authors.initials: S
authors.lastname: Muallem
mesh_terms: D043383:Adenosylhomocysteinase / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017920:Antiporters / Q000235:genetics / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism*; D002460:Cell Line; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism*; D045604:Extracellular Fluid / Q000378:metabolism*; D005260:Female; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D010183:Pancreatic Ducts / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics / Q000378:metabolism*; D000076988:Sulfate Transporters
chemical_list: D017920:Antiporters; D001639:Bicarbonates; D034741:RNA, Small Interfering; C498898:SLC4A4 protein, human; C466900:Slc26a6 protein, mouse; D027982:Sodium-Bicarbonate Symporters; D000076988:Sulfate Transporters; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D043383:Adenosylhomocysteinase; C510392:IRBIT protein, mouse