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Human endothelial cells are target for platelet-activating factor. I. Platelet-activating factor induces changes in cytoskeleton structures.

Platelet-activating factor (PAF), but not its deacetylated and biologically inactive metabolite lyso-PAF, in a dose dependent-manner (0.1 to 10 nM), induces human endothelial cells (EC) in culture to change their shape. EC retract and tend to lose reciprocal contact, whereas the distribution of stress fibers is changed and the cells tend to assume a migratory phenotype. The normal localization of vinculin at streaks corresponding to adhesion plaques and located at stress fiber endings is mostly lost and replaced by diffuse distribution of this protein related to the cell-substratum adhesion complex. The effects of PAF are appreciable after 10 min, become maximal after 30 min, and are fully reversible. The disappearance of F-actin in stimulated EC was analyzed by measuring the fluorescence of the cells after staining with fluorosceinated phalloidin, PAF, but not lyso-PAF and the enantiomer of PAF ([S] form), decreases in a time- and concentration-dependent fashion the fluorescence of the cells stained with fluoresceinated phalloidin. EC grown on fibronectin-coated polycarbonate filters restrict the diffusion of 125I-albumin; PAF promotes 125I-albumin diffusion with a concentration dependency similar to that for the PAF-induced cytoskeleton changes. Four different PAF-receptor antagonists belonging to four different series, CV-3988 (PAF-related framework), BN52021 (a natural terpenoid), BN53013 (a natural lignan) and 48740 RP (a synthetic antagonist) prevent the alteration induced by PAF. These findings, coupled to the lack of effect of the enantiomer of PAF ([S] form), support the existence of a specific mechanism of PAF-mediated activation of EC, most probably mediated by a putative receptor. These results explain part of the PAF mechanism of action in inducing the increase of vascular permeability in vivo.