Claudins are proteins located in the tight junctions (TJ) of epithelial cells where they regulate paracellular permeability. We investigated expression, localisation, and physiological function of the predominantly renal claudin-10. Six mouse claudin-10 isoforms were identified by cloning homologous genes based on human and mouse whole genome sequences and stably transfected into high-resistance MDCK-C7 cells. Vector-only transfected cells served as controls.

Results: Investigation of subcellular distribution by confocal laser scanning microscopy showed that only the isoforms a, b, and a-19 were localized in the plasma membrane, while 3 other isoforms were found in the ER or in vesicles beneath the membrane. Measurements of ion selectivity in the Ussing chamber revealed that claudin-10 isoform b expressing cell layers had a clearly higher paracellular permeability for cations than for anions. Within the monovalent cations, these cell layers exhibited a preference for Na+ > Li+ > K+ > Rb+ > Cs+ , corresponding to the Eisenman sequence X for alkali metals, while relative permeabilities for these ions in control cells followed Eisenman sequence III: Rb+ > K+ > Cs+ > Na+ > Li+ .

Conclusion: While the tight junctions of vector control cells exhibit weak field-strength binding sites for monovalent cations, expression of claudin-10 isoform b causes a cation permeability characterized by strong field-strength binding sites.