pH Dependence on SN-38 uptake by OATP2B1 in Xenopus oocytes
For evaluation of lactone and carboxylate forms of SN-38, SN-38 (0.1 μM) was preincubated in phosphate buffer at pH 3.0 or 9.0, respectively, overnight before the uptake measurement. Then uptake by Xenopus oocytes was measured at pH 6.5 or 8.0 for 10 minutes. Uptake by water-injected oocytes, OATP2B1-expressing oocytes, and the OATP2B1-mediated uptake (shown as “Difference” in the table) was obtained subtraction of the former from the latter and are each shown as the mean ± S.E.M. (n = 7–10).
| Uptake (μl/10 min·oocyte) | ||||||
|---|---|---|---|---|---|---|
| Water-Injected Oocytes | OATP2B1-Expressing Oocytes | Difference (OATP2B1-Mediated) | ||||
| Uptake pH | ||||||
| Preincubation pH | 6.5 | 8.0 | 6.5 | 8.0 | 6.5 | 8.0 |
| 3.0 | 0.605 ± 0.04 | 0.459 ± 0.07 | 0.931 ± 0.08 | 0.590 ± 0.06 | 0.327 ± 0.080 | 0.140 ± 0.065 |
| 9.0 | 0.267 ± 0.04 | 0.159 ± 0.01 | 0.420 ± 0.06 | 0.281 ± 0.04 | 0.174 ± 0.043 | 0.132 ± 0.041 |