title: An alternate pathway of cAMP-stimulated Cl secretion across the NKCC1-null murine duodenum.
abstract: OBJECTIVE
  Adenosine 3',5'-cyclic monophosphate (cAMP)-stimulated anion secretion across the duodenal epithelium requires the cystic fibrosis transmembrane conductance regulator (CFTR) in the apical membrane and anion uptake proteins in the basolateral membrane. NKCC1, the epithelial Na(+)/K(+)/2Cl(-) cotransporter, is the major protein responsible for Cl(-) uptake. In this study, we evaluate the role of NKCC1 in determining the relative rates of transepithelial Cl(-) and HCO(3)(-) secretion during cAMP stimulation of the duodenum.
  
  
  METHODS
  Bicarbonate and chloride secretion across duodenal mucosa was measured in Ussing chambers by pH stat and (36)Cl flux methods using mice with either gene-targeted deletion of NKCC1 (NKCC1-/-) or bumetanide blockade of NKCC1.
  
  
  RESULTS
  Total anion secretion stimulated by forskolin treatment of NKCC1-null duodenum resulted from approximately equivalent rates of electrogenic chloride, electrogenic bicarbonate, and electroneutral bicarbonate secretion. Evaluation of the alternate chloride secretory pathway indicated chloride uptake by a basolateral membrane anion exchange process with characteristics consistent with the anion exchanger isoform AE2.
  
  
  CONCLUSIONS
  Chloride uptake by basolateral anion exchanger activity (AE2) supports intracellular cAMP-stimulated chloride secretion in the NKCC1-null duodenum. A model for the alternate chloride secretion pathway is proposed whereby chloride uptake via AE2 is coupled to basolateral NaHCO(3) cotransport to support CFTR-mediated chloride and bicarbonate secretion.
authors.affiliation: Dalton Cardiovascular Research Center and the Department of Biomedical Sciences, University of Missouri-Columbia, Columbia, Missouri 65211, USA.
authors.forename: Nancy M
authors.initials: NM
authors.lastname: Walker
authors.forename: Michael
authors.initials: M
authors.lastname: Flagella
authors.forename: Lara R
authors.initials: LR
authors.lastname: Gawenis
authors.forename: Gary E
authors.initials: GE
authors.lastname: Shull
authors.forename: Lane L
authors.initials: LL
authors.lastname: Clarke
mesh_terms: D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000502:physiology; D004386:Duodenum / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D051379:Mice; D018345:Mice, Knockout; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology; D028021:Sodium-Potassium-Chloride Symporters / Q000235:genetics / Q000502:physiology*
chemical_list: D002712:Chlorides; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D000242:Cyclic AMP