TABLE 2

Saturation kinetics of OATP1B1-mediated uptake of [³H]E₂G, [³H]E₁S, and [³H]BSP in the presence and absence of unlabeled E₂G, E₁S, and BSP

Kinetic parameters were estimated by nonlinear regression analysis based on Eq. 3 or 4 under Materials and Methods, and are shown as mean ± S.D. (n=3).

Inhibitors	Substrates
	[³H]E₂G^{^a}			[³H]E₁S^{^b}		[³H]BSP^{^c}
	K_m	V_max	P_dif	K_m	V_max	K_m	V_max
	μM	pmol/min/mg	µl/min/mg	µM	pmol/min/mg	µM	pmol/min/mg
No inhibitor	8.17 ± 2.28	250 ± 89	NA	0.286 ± 0.054	36.4 ± 10.3	0.280 ± 0.041	20.8 ± 1.0
E₂G	NA	NA	NA	0.488 ± 0.072^*	35.7 ± 8.3	0.361 ± 0.069	18.5 ± 1.9
E₁S	18.7 ± 2.2**	251 ± 22	NA	NA	NA	4.78 ± 0.65**	111 ± 18**
BSP	5.80 ± 2.53	55.8 ± 24.7**	0.667 ± 0.642	0.677 ± 0.112^*	34.3 ± 11.7	NA	NA

NA, not applicable.
↵^a Concentration-dependent uptake of [³H]E₂G (0.003–100 µM) for 5 min was examined in the absence and presence of unlabeled E₁S (0.1 µM) or BSP (0.3 µM).
↵^b Concentration-dependent uptake of [³H]E₁S (0.003–10 µM) for 1 min was examined in the absence and presence of unlabeled E₂G (10 µM) or BSP (0.3 µM).
↵^c Concentration-dependent uptake of [³H]BSP (0.007–10 µM) for 5 min was examined in the absence and presence of unlabeled E₂G (10 µM) or E₁S (10 µM).
↵* P < 0.05; **P < 0.01 compared with parameters determined without any inhibitors.