HUMAN ENDOTHELIAL-CELLS ARE TARGETS FOR PLATELET-ACTIVATING-FACTOR (PAF) .3. ACTIVATION OF ALPHA-PROTEIN AND BETA-PROTEIN KINASE-C ISOZYMESIN ENDOTHELIAL-CELLS STIMULATED BY PAF

We evaluated the role of the protein kinase C (PKC) and its isozymes i n the activation of human endothelial cells (EC) stimulated by platele t-activating factor (PAF). Exposure of confluent EC to PAF resulted in a rapid and concentration-dependent redistribution of PKC from cytoso l to plasma-membrane, rearrangement of cytoskeleton (i.e. decrease in F-actin content and redistribution of vinculin), and finally increase in the transendothelial flux of I-125-albumin. Stimulation of EC with oleylacetylglycerol or phorbol 12-myristate 13-acetate induced the mod ification of the cytoskeletal structures and the increase of I-125-alb umin clearance. Inhibitors of PKC prevented the effects induced by PAF on the cytoskeleton and on the barrier function of the EC monolayer. Confluent EC expressed only alpha, beta, and epsilon PKC isoforms. Bio chemical and immunochemical analysis showed that the time course of th e PKC isozymes translocation from cytosol to the membrane fraction of EC stimulated by PAF was different: beta isoform was redistributed mor e quickly than alpha isoform. PAF did not induce translocation of PKC epsilon. These results suggest that activation of PKC alpha and beta i s an important signal transduction pathway by which PAF activates endo thelial monolayer and modify its function of barrier to macromolecules .