Uptake of CCK-8 by HEK293 cells transfected with OATP1B1, 1B3 and chimeras 1B3_T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11 and T12. Uptake of 0.1 μM CCK-8 was measured at 37 °C for 1 min with empty vector and OATP-expressing HEK293 cells. The net uptakes were obtained by subtracting the uptake of cells transfected with empty vector from the uptake of OATP-expressing cells. Final results were obtained by normalizing net uptakes to the surface expression levels of the respective proteins. * p < 0.05 significantly different from OATP1B3.