TABLE 1

Effect of pHo on Oatp1a1-, OATP1B1-, and OATP1B3-mediated TCA, E₂17βG, and E3S uptake by transfected CHO cells

Stably transfected CHO cells were incubated in uptake medium (96 mM choline chloride, 5.3 mM KCl, 1.1 mM KH₂PO₄, 0.8 mM MgSO₄, 1.8 mM CaCl₂, 11 mM glucose, and 50 mM HEPES) containing the desired substrate (10 μM [³H]TCA, 10 μM [³H]E₂17βG, or 50 μM [³H]E3S) at 37°C for 15 min. Net uptake values are means ± S.D. from at least nine determinations per data point, obtained using cells from three different cultures.

	Oatp1a1	OATP1B1	OATP1B3
	pmol · mg protein⁻¹ · 15 min⁻¹
10 μM TCA
pH 7.4	11 ± 2	38 ± 4	35 ± 3
pH 6.5	22 ± 2^{^a}	28 ± 5^{^a}	55 ± 7^{^a}
10 μM E₂17βG
pH 7.4	274 ± 20	203 ± 37	63 ± 8
pH 6.5	393 ± 15^{^a}	135 ± 17^{^a}	132 ± 19^{^a}
50 μM E3S
pH 7.4	1446 ± 71	456 ± 51	325 ± 35
pH 6.5	2212 ± 187^{^a}	573 ± 73	479 ± 26^{^a}

↵a P < 0.05, on comparing pH 6.5 with pH 7.4 by paired t test.