Abstract
Tight junction (TJ) is an important adhesion system in epithelial cells, and also plays a role for regulation of paracellular flux across epithelial sheets. Claudins, a component of TJ, comprise a large family consisting of more than 20 members in mammals, and contribute to regulation of barrier function. We have compared expression of claudins in culture and intact duct cells of the rat submandibular gland with that in MDCK cells, a typical epithelial cell line. SMIE cells derived from rat submandibular duct were kindly provided by Dr. B. J. Baum (NIDCR). Duct cells were isolated from rat submandibular gland. TJ proteins were detected by western blotting. Immunofluorecence strain of TJ proteins was observed by a confocal laser scanning microscope. SMIE cells formed TJ as well as MDCK cells, which was confirmed by immunofluorecence strain of the TJ proteins occludin and ZO-1. Claudin-3 protein was detected in both cells. Claudin-1 and claudin-4 proteins were detected in MDCK cells, but not in SMIE cells, which was confirmed by immunofluorecence strain of claudins. However, in rat submandibular duct cells, claudin-4 was detected by western blotting and immunofluorecence strain. In SMIE cells, the transepithelial electrical resistance was lower and the flux of FITC-dextran was higher than in MDCK cells, indicating that SMIE cells are more permeable than MDCK cells. These results suggest that claudin-4 expression contributes to barrier function of intact salivary gland duct cells. [J Physiol Sci. 2006;56 Suppl:S122]
