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Claudins create charge-selective channels in the paracellular pathway between epithelial cells
Oscar R Colegio1, Christina M Van Itallie, Heather J McCrea
1Department of Medicine, Yale University School of Medicine, New Haven, Connecticut 06520, USA. oscar.colegio@yale.edu
American Journal of Physiology. Cell Physiology
|June 11, 2002
Summary
Researchers investigated how claudin proteins in tight junctions control what passes between cells. Modifying claudin charges altered ion selectivity, demonstrating their role in creating charge-selective channels for paracellular transport.
Area of Science:
- Cell Biology
- Biophysics
- Physiology
Background:
- Epithelia maintain tissue separation via regulated ion, solute, and water passage.
- Paracellular permeability is governed by intercellular tight junctions, exhibiting diverse properties.
- Claudins, a family of tight junction proteins, are hypothesized to confer charge selectivity.
Purpose of the Study:
- To test if claudin proteins generate charge selectivity in paracellular pathways.
- To investigate the impact of altering amino acid charges within claudin extracellular domains.
Main Methods:
- Site-directed mutagenesis was used to modify charge at specific amino acid positions in claudins.
- Claudins were expressed in Madin-Darby canine kidney cell monolayers.
- Transmonolayer electrical resistance and dilution potentials were measured.
- Protein expression, localization, and ultrastructure were assessed via immunoblotting, immunofluorescence, and electron microscopy.
Main Results:
- Mutating claudin-4 to introduce a negative charge increased paracellular sodium (Na+) permeability.
- Mutating claudin-15 to introduce positive charges reversed selectivity from Na+ preference to chloride (Cl-) preference.
- These charge alterations directly impacted ion flux across epithelial monolayers.
Conclusions:
- Claudin proteins play a critical role in establishing charge selectivity within tight junctions.
- The extracellular domains of claudins act as determinants for ion channel function.
- These findings support a model where claudins form charge-selective channels in the paracellular space.