Inhibition of apoptosis by rwt APC and APC variants requires PAR-1 and EPCR. PAR-1 and EPCR dependence for inhibition of staurosporine-induced endothelial cell apoptosis by rwt APC and anticoagulantly impaired APC variants was studied using blocking antibodies against PAR-1 (□; combination of WEDE-15 at 20 μg/mL and ATAP-2 at 15 μg/mL) or EPCR (; rabbit anti-EPCR at 20 μg/mL). ▪ represents no antibodies added. Cells were incubated with rwt APC or APC variants (5 nM) 5 hours prior to induction of apoptosis by staurosporine (10 μM, 1 hour). Apoptosis was analyzed by the uptake of Apopercentage dye and expressed as a percentage relative to the percentage of apoptotic cells observed in the absence of added APC (20% of all cells), which was set as 100%. ▥ represents relative apoptosis in the absence of APC and staurosporine. Each bar represents the mean ± SEM from at least 3 independent experiments.