Expression of zonula occludens and adherens junctional proteins in human venous and arterial endothelial cells: Role of occludin in endothelial solute barriers

Objective: The purpose of this study was to correlate the expression of occ ludin and VE-cadherin with the solute barrier properties of arterial and ve nous endothelial monolayers. Methods: Immunofluorescent confocal and traditional microscopy were used to determine junctional protein localization in endothelium in vivo and in vi tro respectively, and western and northern analysis used to determine prote in and gene expression levels. Permeability of endothelial monolayers was e xamined under normal, low calcium, and cytochalasin-D treatment conditions. Antisense oligonucleotide experiments for occludin were performed to deter mine the contribution of occludin to solute barrier. Results: Occludin protein in endothelial monolayers is more concentrated in arterial junctions than in venous junctions both bn vivo and in vitro. Art erial endothelial cells express 18-fold more occludin protein and nine time s more occludin mRNA compared to venous endothelial cells. In vivo, both en dothelial cells demonstrate VE-cadherin staining; and in vitro, only venous endothelial cells express VE-cadherin protein and mRNA. Occludin antisense experiments suggest that both arterial and venous barrier properties are d ue to these different amounts of occludin expression. Venous barrier was re markably sensitive to low extracellular calcium, while arterial barrier was more sensitive to cytochalasin-D. Conclusions: These findings suggest strongly that arterial and venous endot helial barrier reflects the level of expression of different adhesion molec ules and that modulation of these proteins? especially occludin? may regula te the level of endothelial solute barrier.