NAADP is essential for VWF release specifically activated through H1R. Measurement of secreted VWF by ELISA assay in HUVECs. Cells were treated either with vehicle alone or with 100μM Ned-19 or with 100μM cimetidine (H2R antagonist), or with 100μM Ned-19 and 100μM cimetidine for 30 minutes before stimulation with agonists as indicated in panels A and B. cime indicates cimetidine. Error bars represent SEM; n = 3 independent experiments; *P < .05 by Student t test.