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 pho rbol myristate acetate (PMA) can stimulate endocytosis in bovine aorti c endothelial cells. Moreover, we have found that redistribution of fi lamentous actin (F-actin) in a low concentration of cytochalasin B als o increases such endocytic activity. In the present study, the effects of H2O2 and PMA on endothelial transport and F-actin distribution wer e studied in bovine aortic endothelial monolayers. A low concentration of H2O2 (10(-5) M) had no effect on permeability, but did cause redis tribution of F-actin, i.e., the diffuse arrangement of filaments chang ed 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 eff ect on F-actin structure either, whereas 5 X 10(-7) M PMA caused decre ased permeability during the first 1 to 1.5 h and thereafter increased permeability for up to 6 h. There was also a time-dependent reorganiz ation of F-actin structure after the treatment with 5 X 10(-7) PMA: th e number of dense peripheral bands increased after 1 h of exposure; th ese 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 c ontrols the paracellular pathway of vascular permeability. (C) 1995 Ac ademic Press, Inc.