title: Claudin-2 expression induces cation-selective channels in tight junctions of epithelial cells.
abstract: Tight junctions seal the paracellular pathway of epithelia but, in leaky tissues, also exhibit specific permeability. In order to characterize the contribution of claudin-2 to barrier and permeability properties of the tight junction in detail, we studied two strains of Madin-Darby canine kidney cells (MDCK-C7 and MDCK-C11) with different tight junctional permeabilities. Monolayers of C7 cells exhibited a high transepithelial resistance (>1 kOhms cm(2)), compared with C11 cells (<100 Ohms cm(2)). Genuine expression of claudin-1 and claudin-2, but not of occludin or claudin-3, was reciprocal to transepithelial resistance. However, confocal microscopy revealed a marked subjunctional localization of claudin-1 in C11 cells, indicating that claudin-1 is not functionally related to the low tight junctional resistance of C11 cells. Strain MDCK-C7, which endogenously does not express junctional claudin-2, was transfected with claudin-2 cDNA. In transfected cells, but not in vector controls, the protein was detected in colocalization with junctional occludin by means of immunohistochemical analyses. Overexpression of claudin-2 in the originally tight epithelium with claudin-2 cDNA resulted in a 5.6-fold higher paracellular conductivity and relative ion permeabilities of Na(+) identical with 1, K(+)=1.02, NMDG(+)=0.79, choline(+)=0.71, Cl(-)=0.12, Br(-)=0.10 (vector control, 1:1.04:0.95:0.94:0.85:0.83). By contrast, fluxes of (radioactively labeled) mannitol and lactulose and (fluorescence labeled) 4 kDa dextran were not changed. Hence, with regular Ringer's, Na(+) conductivity was 0.2 mS cm(-2) in vector controls and 1.7 mS cm(-2) in claudin-2-transfected cells, while Cl(-) conductivity was 0.2 mS cm(-2) in both cells. Thus, presence of junctional claudin-2 causes the formation of cation-selective channels sufficient to transform a 'tight' tight junction into a leaky one.
authors.affiliation: Department of Clinical Physiology, Benjamin Franklin Medical School, Freie Universität Berlin, Hindenburgdamm 30, 12200 Berlin, Germany.
authors.forename: Salah
authors.initials: S
authors.lastname: Amasheh
authors.forename: Noga
authors.initials: N
authors.lastname: Meiri
authors.forename: Alfred H
authors.initials: AH
authors.lastname: Gitter
authors.forename: Torsten
authors.initials: T
authors.lastname: Schöneberg
authors.forename: Joachim
authors.initials: J
authors.lastname: Mankertz
authors.forename: Jörg D
authors.initials: JD
authors.lastname: Schulzke
authors.forename: Michael
authors.initials: M
authors.lastname: Fromm
mesh_terms: D000818:Animals; D001483:Base Sequence; D002412:Cations; D002460:Cell Line; D057167:Claudins; D017931:DNA Primers; D004285:Dogs; D005455:Fluorescent Antibody Technique; D007473:Ion Channels / Q000096:biosynthesis*; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D014162:Transfection
chemical_list: D002412:Cations; D057167:Claudins; C113371:Cldn2 protein, mouse; D017931:DNA Primers; D007473:Ion Channels; D008565:Membrane Proteins