Quantification of the cell-surface endoglin and TβRII using cell ELISA. HAECs and HUVECs were stimulated with thrombin (3 U/mL) for indicated time periods. Cell-surface receptors were measured by using cell ELISA with antibodies against the NH₂-terminus of endoglin, PAR1, ALK5, and TβRII. (A) ○ indicates HUVEC-endoglin; •, HAEC-endoglin; ▴, HAEC-PAR1. (B) • indicates HAEC-ALK5; ○, HAEC-TβRII; ▾, HUVEC-TβRII. Results shown are representative of 3 independent experiments. *P < .05. Error bars indicate standard deviation.