Hyperoxia causes increased albumin permeability of cultured endothelial monolayers

When confluent calf pulmonary arterial endothelial monolayers cultured on polycarbonate micropore membranes were exposed to hyperoxia (95% O2) for 3 days, endothelial cells became enlarged, and their permeability to 125I-labeled albumin was markedly increased. Similar changes were not observed when endothelial monolayers were exposed to hyperoxia for 1 or 2 days. Cell counting and acridine orange staining of endothelial monolayers revealed that the hyperoxia-induced increase in albumin permeability was not associated with a denuding injury or loss of cells from the monolayers. Vimentin filament staining of O2-exposed monolayers showed thickening of the perinuclear vimentin coil in some cells. Rhodamine-phalloidin staining demonstrated that hyperoxia caused a progressive alteration in the actin distribution. Two days after O2 exposure, peripheral actin bands became thinner, whereas the number of cytoplasmic stress fibers was increased. Three days after O2 exposure, peripheral actin bands of most cells were disrupted or absent. Because peripheral actin bands play an important role in maintaining the integrity of endothelial monolayers, disruption of peripheral bands by hyperoxia may in part be responsible for the observed change in permeability.