Fig. (6) Effect of progesterone on OATP1B1- and OATP1B3-mediated FMTX uptake. Concentration dependent inhibition of OATP1B1-mediated and stimulation of OATP1B3-mediated 5 µM FMTX uptake was measured for 30 min at room temperature on 96-well plates with wild-type and OATP-expressing CHO cells. Values obtained with wild-type CHO cells were subtracted from values obtained with OATP-expressing cells and are given as percent of control. Means ± SE of two combined independent experiments each performed in quadruplicates are shown and were used to calculate IC₅₀ and EC₅₀ values, respectively.