The paracellular barrier of epi- and endothelia is established by the particular arrangement of claudins, a protein family located within the tight junction. We analyzed the expression of claudins in human umbilical vein endothelial cells (HUVEC) and compared the effect of physiological shear stress as occurring during normal blood flow with that of zero shear stress as occurring after obliteration.

HUVEC were cultured on Petri dishes. After reaching confluence, monolayers were exposed for 24 h to a shear stress in a cone-and- plate device. Transcription and expression of tight junction proteins were analyzed by Western blotting, confocal laser- scanning microscopy, and TaqMan PCR.

In HUVEC, occludin and claudin-5 were detected within the tight junction. As a main result, at zero shear stress transcription and expression of claudin-5 were increased as compared to 6 dyn/cm2 shear stress.

We demonstrate that claudin-5, the main barrier-forming protein of endothelial tight junctions, is down-regulated in HUVEC by shear stress. Increased claudin-5 expression at zero shear stress would indicate that after stasis of blood flow solute transfer into surrounding tissues would be counter acted by this mechanism.