Openings through endothelial cells associated with increased microvascularpermeability

Rapid increases in microvascular permeability are associated with the appea rance of openings in microvascular endothelium; which are believed to devel op between the endothelial cells of venules. Reconstruction of these openin gs, from electron micrographs of serial sections of the endothelium reveal that many pass through the periphery of the endothelial cells close to inta ct intercellular junctions. Transcellular pathways are the principal type o f opening induced in microvascular endothelium by the ionophore A23187, by VEGF, and by high transmural pressures. Some mediators induce the fusion of vacuoles with the luminal and abluminal surfaces of the endothelium, and i t is suggested that the transcellular openings may develop from vacuolar ch annels.