Phosphoinositide hydrolysis in endothelial cells from neonatal skin and lung. Endothelial cells were isolated from mice of the indicated genotype, labeled with [³H]-myoinositol, then incubated with vehicle, scrambled PAR4 agonist (YAPGKF; 500 μM), PAR4 agonist (AYPGKF; 500 μM), or α-thrombin (10 nM) for 2 hours. Data shown are mean fold increases (± SD) in [³H]-inositol phosphate accumulation normalized to vehicle control (n = 4). Each experiment was reproduced at least 3 times except for that using Par1–/–;Par4–/– lung endothelial cells (Par1,4–/–), which was performed only once because of the difficulty of generating adequate numbers of Par1,4–/– mice. Responses to the PAR2 agonist SLIGRL (100 μM) were also measured in each of the experiments shown; all endothelial cell preparations, regardless of genotype, showed robust responses (A) 10- to 20-fold in endothelial cell preparations from skin and (B) 8- to 10-fold in preparations from lung.