F9CH γ-carboxylation in HEK-C3 cells is differentially inhibited by warfarin enantiomers and metabolites. (A) Doxycycline-induced, vitamin K1–supplemented HEK-C3 cells cultured in increasing concentrations of S warfarin, R warfarin or R,S-warfarin were assayed by flow cytometry for γ-carboxylated F9CH and DsRed fluorescence as described. Log-transformed data from individual experiments (n = 4) were plotted. (B) Doxycycline-induced, vitamin K1–supplemented HEK-C3 cells cultured in increasing concentrations of racemic warfarin metabolites were assayed by flow cytometry for F9CH Gla and DsRed fluorescence as described. Curves represent log-transformed data from multiple experiments (n = 3-4).