Effect of heparin on aPC generation on TM-K293 cells. (A) Effect of heparin on aPC generation on TM-K293 cells in the presence of 3 different concentrations of PF4: below (0.4μM), near (1.6μM), or above (12.8μM) maximal aPC stimulation activity. Data are mean ± SD of 3 or 4 experiments, each performed in duplicate. *P < .01 vs no heparin. (B) Various amounts of heparin were added to TM cells in the presence of 4μM PRT, a concentration above peak aPC stimulation. Graphs represent the mean ± SD of 3 experiments, each performed in duplicate. *P < .01 vs no heparin. Heparin activity was 196 U/mg, which corresponds to 3 U/mL for 1μM of heparin in the assay mix.