title: ClC-2 in guinea pig colon: mRNA, immunolabeling, and functional evidence for surface epithelium localization.
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.
authors.affiliation: Centro de Estudios Científicos, Valdivia, Chile.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Catalán
authors.forename: Isabel
authors.initials: I
authors.lastname: Cornejo
authors.forename: Carlos D
authors.initials: CD
authors.lastname: Figueroa
authors.forename: María Isabel
authors.initials: MI
authors.lastname: Niemeyer
authors.forename: Francisco V
authors.initials: FV
authors.lastname: Sepúlveda
authors.forename: L Pablo
authors.initials: LP
authors.lastname: Cid
mesh_terms: D000818:Animals; D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels / Q000032:analysis / Q000235:genetics* / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism; D003106:Colon / Q000737:chemistry*; D004553:Electric Conductivity; D004848:Epithelium / Q000737:chemistry; D006168:Guinea Pigs; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007408:Intestinal Absorption; D008297:Male; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000032:analysis*; D011994:Recombinant Proteins; D012965:Sodium Chloride / Q000378:metabolism
chemical_list: D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels; D002712:Chlorides; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012965:Sodium Chloride