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Claudin‐2 Mediates Sodium and Water Transport through a Common Pore
Author(s) -
Rosenthal Rita,
Günzel Dorothee,
Schulzke Joerg,
Fromm Michael,
Yu Alan
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.970.14
Subject(s) - claudin , paracellular transport , chemistry , sodium , biophysics , extracellular , tight junction , permeability (electromagnetism) , sodium channel , cysteine , amino acid , biochemistry , membrane , biology , enzyme , organic chemistry
Background The tight junction protein Claudin‐2 is mostly expressed in leaky epithelia like proximal kidney tubule and small intestine. Claudin‐2 protein abundance is increased in inflammatory bowel diseases like Crohn's disease, ulcerative colitis, and celiac disease. Former studies of our group revealed that claudin‐2 forms paracellular channels for small cations like sodium and potassium and also paracellular channels for water. Aim of this study was to analyze whether the diffusive transport of sodium and water occurs through a common pore of the claudin‐2 channel. Methods Wild‐type claudin‐2 and claudin‐2 mutants with substituted amino acids of the first extracellular loop were expressed in the tight epithelial cell line MDCK I, using a TetOff inducible system. Sodium and water permeability were measured in modified Ussing chambers. Results Neutralization of the negatively charged cation interaction site in the pore with the mutation D65N caused a reduction of both, sodium and water permeability. Steric blocking of the claudin‐2 pore by thiol‐reactive reagents was performed after substitution of the pore‐lining amino acids, isoleucine‐66 and serine‐68 with cysteine. Thiol‐reactive reagents caused a decrease in both, ion conductance and water permeability in these claudin‐2 cysteine mutants whereas wild‐type claudin‐2 was not affected. Plotting all data yielded a strong correlation of claudin‐2‐mediated sodium and water permeability. Conclusion Claudin‐2‐mediated sodium and water transport are loosely coupled and share a common pore lined by the amino acids of the first extracellular loop of claudin‐2.