ClC-2 in guinea pig colon: mRNA, immunolabeling, and functional evidence for surface epithelium localization

Am J Physiol Gastrointest Liver Physiol. 2002 Oct;283(4):G1004-13. doi: 10.1152/ajpgi.00158.2002.

Abstract

The principal function of the colon in fluid homeostasis is the absorption of NaCl and water. Apical membrane Na(+) channels, Na(+)/H(+) and Cl(-)/HCO exchangers, have all been postulated to mediate NaCl entry into colonocytes. The identity of the basolateral exit pathway for Cl(-) is unknown. We have previously demonstrated the presence of the ClC-2 transcript in the guinea pig intestine. Now we explore in more detail, the tissue and cellular distribution of chloride channel ClC-2 in the distal colon by in situ hybridization and immunohistochemistry. The patch-clamp technique was used to characterize Cl(-) currents in isolated surface epithelial cells from guinea pig distal colon and these were compared with those mediated by recombinant guinea pig (gp)ClC-2. ClC-2 mRNA and protein were found in the surface epithelium of the distal colon. Immunolocalization revealed that, in addition to some intracellular labeling, ClC-2 was present in the basolateral membranes but absent from the apical pole of colonocytes. Isolated surface epithelial cells exhibited hyperpolarization-activated chloride currents showing a Cl(-) > I(-) permeability and Cd(2+) sensitivity. These characteristics, as well as some details of the kinetics of activation and deactivation, were very similar to those of recombinant gpClC-2 measured in parallel experiments. The presence of active ClC-2 type currents in surface colonic epithelium, coupled to a basolateral location for ClC-2 in the distal colon, suggests a role for ClC-2 channel in mediating basolateral membrane exit of Cl(-) as an essential step in a NaCl absorption process.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chloride Channels / analysis
  • Chloride Channels / genetics*
  • Chloride Channels / physiology*
  • Chlorides / metabolism
  • Colon / chemistry*
  • Electric Conductivity
  • Epithelium / chemistry
  • Guinea Pigs
  • Immunohistochemistry
  • In Situ Hybridization
  • Intestinal Absorption
  • Male
  • Patch-Clamp Techniques
  • RNA, Messenger / analysis*
  • Recombinant Proteins
  • Sodium Chloride / metabolism

Substances

  • Chloride Channels
  • Chlorides
  • ClC-2 chloride channels
  • RNA, Messenger
  • Recombinant Proteins
  • Sodium Chloride