Fig. 8.

Dixon plots of inhibitory effects of estradiol (a), testosterone (b), progesterone (c) and androstenedione (d) on BCRP-mediated E₁S uptake. Membrane vesicles were incubated with indicated concentrations of [³H]-E₁S and increasing concentrations of the steroid. The reciprocal of transport velocity (1/V) was calculated and the mode of inhibition was determined using Dixon’s method combined with linear regression analysis to estimate the inhibitory constant (K _i) values; a 5.0 ± 0.2 μM; b 36 ± 14 μM; c 14.7 ± 1.3 μM; d 217 ± 13 μM). A representative of one experiment, out of three independent measurements, is depicted