EFFECTS OF HYDROGEN-PEROXIDE AND PHORBOL-MYRISTATE ACETATE ON ENDOTHELIAL TRANSPORT AND F-ACTIN DISTRIBUTION

We have previously reported that both hydrogen peroxide (H2O2) and phorbol myristate acetate (PMA) can stimulate endocytosis in bovine aortic endothelial cells. Moreover, we have found that redistribution of filamentous actin (F-actin) in a low concentration of cytochalasin B also increases such endocytic activity. In the present study, the effects of H2O2 and PMA on endothelial transport and F-actin distribution were studied in bovine aortic endothelial monolayers. A low concentration of H2O2 (10(-5) M) had no effect on permeability, but did cause redistribution of F-actin, i.e., the diffuse arrangement of filaments changed to a clear stress-fiber pattern, but the dense peripheral filament bands were not affected. A 10-fold higher concentration of H2O2 (10(-4) M), which increases permeability as we reported previously, caused a disruption of F-actin dense peripheral bands. PMA had a concentration-dependent effect on endothelial permeability and F-actin distribution, i.e., 10(-7) M PMA had no observed effect on permeability and no effect on F-actin structure either, whereas 5 X 10(-7) M PMA caused decreased permeability during the first 1 to 1.5 h and thereafter increased permeability for up to 6 h. There was also a time-dependent reorganization of F-actin structure after the treatment with 5 X 10(-7) PMA: the number of dense peripheral bands increased after 1 h of exposure; these bands had a ruffled appearance after 2 h and were disrupted after 6 h. These results suggest that, in endothelial cells, F-actin plays a role in regulating the width of intercellular junctions and thereby controls the paracellular pathway of vascular permeability. (C) 1995 Academic Press, Inc.