Effect of warfarin on FIXgla-PC carboxylation in HEK293 cells. (A) Cells grown in culture medium with either 11μM vitamin K (○) or 5μM KO (●) were incubated for 48 hours with increasing concentrations of warfarin. The concentration of carboxylated FIXgla-PC in the medium was measured by ELISA. The data are presented as percentages to make the first concentration points of vitamin K and KO coincide. (B) Cells were grown with (○) or without (●) 2μM warfarin in increasing concentrations of vitamin K for 48 hours. The concentration of carboxylated FIXgla-PC in the culture medium was measured by ELISA.