title: cAMP-dependent and cholinergic regulation of the electrogenic intestinal/pancreatic Na+/HCO3- cotransporter pNBC1 in human embryonic kidney (HEK293) cells.
abstract: BACKGROUND
  The renal (kNBC1) and intestinal (pNBC1) electrogenic Na+/HCO3- cotransporter variants differ in their primary structure, transport direction, and response to secretagogues. Previous studies have suggested that regulatory differences between the two subtypes can be partially explained by unique consensus phosphorylation sites included in the pNBC1, but not the kNBC1 sequence. After having shown activation of NBC by carbachol and forskolin in murine colon, we now investigated these pathways in HEK293 cells transiently expressing a GFP-tagged pNBC1 construct.
  
  
  RESULTS
  Na+- and HCO3-dependent pHi recovery from an acid load (measured with BCECF) was enhanced by 5-fold in GFP-positive cells compared to the control cells in the presence of CO2/HCO3-. Forskolin (10(-5) M) had no effect in untransfected cells, but inhibited the pHi recovery in cells expressing pNBC1 by 62%. After preincubation with carbachol (10(-4) M), the pHi recovery was enhanced to the same degree both in transfected and untransfected cells, indicating activation of endogenous alkalizing ion transporters. Acid-activated Na+/HCO3- cotransport via pNBC1 expressed in renal cells is thus inhibited by cAMP and not affected by cholinergic stimulation, as opposed to the findings in native intestinal tissue.
  
  
  CONCLUSIONS
  Regulation of pNBC1 by secretagogues appears to be not solely dependent on its primary structure, but also on properties of the cell type in which it is expressed.
authors.affiliation: Department of Gastroenterology, Hepatology, and Endocrinology, Hannover Medical School, Hannover, Germany. bachmann.oliver@mh-hannover.de
authors.forename: Oliver
authors.initials: O
authors.lastname: Bachmann
authors.forename: Kristin
authors.initials: K
authors.lastname: Franke
authors.forename: Haoyang
authors.initials: H
authors.lastname: Yu
authors.forename: Brigitte
authors.initials: B
authors.lastname: Riederer
authors.forename: Hong C
authors.initials: HC
authors.lastname: Li
authors.forename: Manoocher
authors.initials: M
authors.lastname: Soleimani
authors.forename: Michael P
authors.initials: MP
authors.lastname: Manns
authors.forename: Ursula
authors.initials: U
authors.lastname: Seidler
mesh_terms: D001639:Bicarbonates / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D018679:Cholinergic Agonists / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D017136:Ion Transport; D012964:Sodium / Q000378:metabolism*; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D018679:Cholinergic Agonists; C498898:SLC4A4 protein, human; D027982:Sodium-Bicarbonate Symporters; D002217:Carbachol; D012964:Sodium; D000242:Cyclic AMP