Bicarbonate secretion by rat bile duct brush cells indicated by immunohistochemical localization of CFTR, anion exchanger AE2, Na+/HCO3 -cotransporter, carbonic anhydrase II, Na+/H+ exchangers NHE1 and NHE3, H+/K+-ATPase, and Na+/K+-ATPase.
The function of brush cells (BCs) is unknown. In a previous study, the rat common bile duct was examined by ultrastructural cytochemical methods for localizing HCO(3) (-), Cl(-), and Na(+) ions. All ion precipitates increased in or on BCs after secretin or meal stimulation, and it was proposed that BCs may secrete NaHCO(3). In this study, immunohistochemical localization of proteins known to be important in HCO(3) (-) secretion was investigated in the rat common bile duct. Immunoreactivity of proteins involved in Cl(-)/HCO(3) (-) exchange reaction, cystic fibrosis transmembrane conductance regulator (CFTR) and Cl(-)/HCO(3) (-) exchanger (AE2), was found on the microvilli (MV) and along the basolateral membrane (BLM) of BCs. The proteins involved in HCO(3) (-) production, Na(+)/HCO(3) (-) cotransporter (NBC), was found along the BLM but was absent on the MV, whereas carbonic anhydrase II (CA II) was observed on the MV and along the BLM. Of proteins responsible for the extrusion of H(+), Na(+)/H(+) exchanger 1 (NHE1) was localized along the BLM whereas Na(+)/H(+) exchanger 3 (NHE3) was found on the MV and BLM. Activity of H(+)/K(+)-ATPase was found along the BLM and on the MV, and Na(+)/K(+)-ATPase was localized along the BLM. The immunoreactivity of most of these proteins was absent or weak in principal cells. These results strongly suggest that BCs are a significant source of HCO(3) (-) secretion.
Department of Surgery and Physiology, Kochi Medical School, Kohasu, Nankoku, Japan. ogatat@kochi-ms.ac.jp
Takuro
T
Ogata
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D027321:Anion Transport Proteins / Q000378:metabolism; D017920:Antiporters / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D001652:Bile Ducts / Q000166:cytology / Q000378:metabolism*; D024402:Carbonic Anhydrase II / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism; D007150:Immunohistochemistry; D008871:Microvilli / Q000378:metabolism*; D021381:Protein Transport; D051381:Rats; D064606:SLC4A Proteins; D027982:Sodium-Bicarbonate Symporters / Q000378:metabolism; D000074082:Sodium-Hydrogen Exchanger 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D027321:Anion Transport Proteins; D017920:Antiporters; D001639:Bicarbonates; D064606:SLC4A Proteins; C452850:Slc9a1 protein, rat; C000613387:Slc9a3 protein, rat; D027982:Sodium-Bicarbonate Symporters; D000074082:Sodium-Hydrogen Exchanger 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D024402:Carbonic Anhydrase II; D000254:Sodium-Potassium-Exchanging ATPase