Quantification of cell surface–exposed PAR1. Confluent EA.hy926 cells were incubated for 3 hours with the indicated agonists. Apical expression of PAR1 was analyzed in a cell-surface ELISA using monoclonal anti-PAR1 antibodies SPAN11, ATAP2, and WEDE15. Results are shown relative to control (means ± SEM, n = 9, **P < .005).