title: Severe defects in absorptive ion transport in distal colons of mice that lack ClC-2 channels.
abstract: OBJECTIVE
  The fluid secretion model predicts that intestinal obstruction disorders can be alleviated by promoting epithelial Cl(-) secretion. The adenosine 3',5'-cyclic monophosphate (cAMP)-activated anion channel CFTR mediates Cl(-)-dependent fluid secretion in the intestine. Although the role of the ClC-2 channel has not been determined in the intestine, this voltage-gated Cl(-) channel might compensate for the secretory defects observed in patients with cystic fibrosis and other chronic constipation disorders. We investigated whether mice that lack ClC-2 channels (Clcn2(-/-)) have defects in intestinal ion transport.
  
  
  METHODS
  Immunolocalization and immunoblot analyses were used to determine the cellular localization and the amount of ClC-2 expressed in mouse early distal colon (EDC) and late distal colon (LDC). Colon sheets from wild-type and Clcn2(-/-) littermates were mounted in Ussing chambers to determine transepithelial bioelectrical parameters and Na(+), K(+), and Cl(-) fluxes.
  
  
  RESULTS
  Expression of ClC-2 was higher in the basolateral membrane of surface cells in the EDC compared with the LDC, with little expression in crypts. Neither cAMP nor Ca(2+)-induced secretion of Cl(-) was affected in the EDC or LDC of Clcn2(-/-) mice, whereas the amiloride-sensitive short-circuit current was increased approximately 3-fold in Clcn2(-/-) EDC compared with control littermates. Conversely, electroneutral Na(+), K(+), and Cl(-) absorption was dramatically reduced in colons of Clcn2(-/-) mice.
  
  
  CONCLUSIONS
  Basolateral ClC-2 channels are required for colonic electroneutral absorption of NaCl and KCl. The increase in the amiloride-sensitive short-circuit current in Clcn2(-/-) mice revealed a compensatory mechanism that is activated in the colons of mice that lack the ClC-2 channel.
authors.affiliation: Secretory Mechanisms and Dysfunction Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Marcelo A
authors.initials: MA
authors.lastname: Catalán
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Flores
authors.forename: Mireya
authors.initials: M
authors.lastname: González-Begne
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Francisco V
authors.initials: FV
authors.lastname: Sepúlveda
authors.forename: James E
authors.initials: JE
authors.lastname: Melvin
mesh_terms: D000818:Animals; D015153:Blotting, Western; D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels / Q000378:metabolism*; D002713:Chlorine / Q000378:metabolism; D003106:Colon / Q000378:metabolism*; D003248:Constipation / Q000378:metabolism; D005260:Female; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism*; D017136:Ion Transport; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D016133:Polymerase Chain Reaction; D011189:Potassium Chloride / Q000378:metabolism; D012965:Sodium Chloride / Q000378:metabolism
chemical_list: D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels; C000715428:Clcn2 protein, mouse; D012965:Sodium Chloride; D002713:Chlorine; D011189:Potassium Chloride
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