Fig. 1. Effects of shear stress and receptor-dependent agonists on the tyrosine phosphorylation of PECAM-1. Primary cultures of human umbilical vein endothelial cells were either maintained under static conditions, exposed to fluid shear stress (Shear; 12 dynes cm^–2, 2-120 minutes) or stimulated with either solvent (CTL), VEGF (100 ng ml^–1, 5-30 minutes), histamine (Hist; 1 µmol l^–1, 10-30 minutes), or ionomycin (Iono; 0.1 µmol l^–1, 10-30 minutes). PECAM-1 was immunoprecipitated and the tyrosine phosphorylation was assessed by western blotting. To verify equal amounts of immunoprecipitated protein the blot was reprobed with an antibody raised against PECAM-1. The western blots shown are representative of data obtained in three independent experiments and the bar graph summarizes data obtained in three independent experiments; ^**P<0.01, ^***P<0.001 versus static conditions.