APC cleaved PAR1 remains on the cell surface. (A) Cells were incubated with agonists for 3 hours in the absence or presence of brefeldin A followed by analysis of ATAP2 or WEDE15 binding by surface ELISA as indicated. Means plus or minus SEM are shown (n = 9). (B) Cells were incubated for 3.5 hours with 100 pM hirudin without or with additional 20 nM of APC. For the final 30 minutes of incubation either control or 500 pM of thrombin was added and cell surface–expressed PAR1 was quantified by analysis of ATAP2 and WEDE15 binding. Means plus or minus SEM are shown (n = 9, **P < .005 comparing results without and with thrombin for final 30 minutes).