Endothelial cell junctional F-actin structures. Human umbilical vein endothelial cells grown as confluent monolayers were fixed and stained for β-catenin to identify cell junctions and phalloidin to label F-actin. (A) Example of cortical actin belts. This cell demonstrates a strong cortical enrichment of F-actin, arranged parallel to cell junctions. Bars, 15 µm. (B) Example of inserted junctional SFs. Another cell exhibits several discontinuous junctions (indicated by asterisks in enlarged merged image), where the insertion of SF ends can be observed. These junctions appear to physically connect SFs between two adjacent endothelial cells. Boxed areas show the area enlarged below. Bars, 25 µm.