Endothelial monolayer integrity. Perturbation of F-actin filaments and the dense peripheral band-vinculin network.

The role of the actin microfilaments in maintaining the integrity of the monolayer and activating endothelial repair processes is not well understood. This study was designed to characterize the prominent changes in F-actin distribution in endothelial cells that are associated with shape changes in the cells after perturbation of a confluent monolayer. F-actin was localized by using rhodamine phalloidin and fluorescence microscopy. The dense peripheral band (DPB) and vinculin cell-cell junctions were co-localized by using double fluorescence and immunofluorescence microscopy. Thrombin and 12-o-tetradecanoyl-myristyl-13-acetate (TPA) caused loss of the DPB and an increase in the central microfilament bundles, while agents that caused rounding of the cells (including plasmin, trypsin, and chymotrypsin) did not cause loss of the DPB although large gaps were formed between cells. The thrombin and TPA effects were rapid and reversible and were associated with an accompanying loss of vinculin cell-cell plaques. The mechanisms of the effects were not studied. It was postulated that thrombin and TPA were activating endothelial repair processes.