Kinetic parameters of the uptake of H2 receptor antagonists by organic cation transporters Km and Vmax were determined by nonlinear regression analysis as described under Materials and Methods. Data are taken from Figs. 3 and 4. Each value represents the mean ± computer-calculated S.D. The value in parentheses represents the relative transport activity with regard to cimetidine transport.
Isoform | Cimetidine | Famotidine | Ranitidine | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Km | Vmax | Vmax/Km | Km | Vmax | Vmax/Km | Km | Vmax | Vmax/Km | |||||||
| μM | pmol / min / mg protein | μl / min / mg protein | μM | pmol / min / mg protein | μl / min / mg protein | μM | pmol / min / mg protein | μl / min / mg protein | |||||||
| hOCT2 | 72.6 ± 13.9 | 2170 ± 240 | 29.9 (1) | 56.1 ± 4.0 | 204 ± 8 | 3.63 (0.12) | 65.2 ± 8.1 | 265 ± 20 | 4.06 (0.14) | ||||||
| rOct1 | 71.5 ± 10.7 | 2210 ± 190 | 30.9 (1) | 86.7 ± 6.2 | 2020 ± 90 | 23.3 (0.75) | 39.2 ± 1.9 | 1050 ± 30 | 26.8 (0.87) | ||||||
| rOct2 | 68.8 ± 8.0 | 1490 ± 100 | 21.7 (1) | 60.6 ± 4.1 | 117 ± 4 | 1.93 (0.09) | N.D. | N.D. | 0.50 (0.02) | ||||||
N.D., not determined.