Inhibition of endothelial cell retraction by ATP depletion.

To determine the relationship among endothelial cell (EC) retraction, cell adenosine triphosphate (ATP), and the status of cellular actin, ATP levels, F-actin content, and cytochemical redistribution in bovine pulmonary artery endothelial cells were assessed. EC monolayers 7 days after confluence were exposed to ethchlorvynol (ECV), histamine, or cytochalasin B (cyto B) for time intervals from 5-90 minutes. All 3 agents resulted in endothelial cell retraction without significant effect on cellular ATP content. Sixty-minute incubation of monolayers in glucose-free media containing antimycin A and 2-deoxyglucose depleted cellular ATP to less than 10% of control levels. ATP depleted monolayers failed to retract when incubated with ECV, histamine, or cyto B. ATP depletion resulted in loss of the prominent EC margins but only a rare gap between adjacent cells. When ATP levels were allowed to recover, the ability of EC monolayers to retract was restored. Actin filaments in control monolayers localized to a dense peripheral band of actin, a paranuclear complex, and bundles of microfilaments orientated parallel to the long axis of the cell. ECV induced complete loss of the dense peripheral band and other changes in the actin disposition. Monolayers exposed to histamine showed a retraction of the dense peripheral band of actin to a subcortical position. Cyto B caused loss of the dense peripheral band and the longitudinal microfilament bundles. Monolayers depleted of ATP lost their dense peripheral band and exhibited a disorganized, tangled web of microfilaments. Neither histamine nor ECV modified the actin distribution in ATP-depleted monolayers, whereas exposure to cyto B resulted in substantial change in actin with formation of a rim inside the cell membrane and considerable loss of actin filaments. ECV or histamine induced a small reduction in F-actin content while cyto B resulted in a 50% decline in 15 minutes. ATP depletion resulted in a 19% decrease in F-actin, with no further reduction on subsequent exposure to histamine or ECV. Cyto B treatment of ATP-depleted monolayers caused a drop in F-actin content equivalent to that observed in cells with normal ATP levels. These studies indicate that ATP is essential for changes in actin filament distribution and endothelial cell retraction produced by ECV, histamine or cyto B, and make it unlikely that any of these agents acts simply by depolymerization of actin filaments or modification of the dense peripheral band, although disruption of the dense peripheral band may facilitate retraction in the presence of adequate levels of cell ATP.