Expression of Zonula Occludens and Adherens Junctional Proteins in Human Venous and Arterial Endothelian Cells: Role of Occludin in Endothelial Solute Barriers

ABSTRACT Objective : The purpose of this study was to correlate the expression of occludin and VE‐cadherin with the solute barrier properties of arterial and venous endothelial monolayers. Methods : Immunofluorescent confocal and traditional microscopy were used to determine junctional protein localization in endothelium in vivo and in vitro respectively, and western and northern analysis used to determine protein and gene expression levels. Permeability of endothelial monolayers was examined under normal, low calcium, and cytochalasin‐D treatment conditions. Antisense oligonucleotide experiments for occludin were performed to determine the contribution of occluding to solute barrier. Results : Occludin protein in endothelial monolayers in more concentrated in arterial junctions than in venous junctions both in vivo and in vitro . Arterial endothelial cells express 18‐fold more occluding protein and nine times more occluding mRNA compared to venous endothelial cells. In vivo , both endothelial cells demonstrate VE‐cadherin staining; in vitro, only venous endothelial cells express VE‐cadherin protein and mRNA. Occludin antisense experiments suggest that both arterial and venous barrier properties are due to these different amounts of occluding expression. Venous barrier was remarkably sensitive to low extracellular calcium, while arterial barrier was more sensitive to cytochalasin‐D. Conclusions : These findings suggest strongly that arterial and venous endothelial barrier reflects the level of expression of different adhesion molecules and that modulation of these proteins, especially occluding, may regulate the level of endothelial solute barrier.