Inhibition of hENT1-, hENT2-, hCNT1-, hCNT2-, and hCNT3-mediated [3H]uridine transport by uridine, adenosine, and tecadenoson
IC50 values for inhibition of [3H]uridine transport by recombinant hNTs in yeast were derived from computer-generated concentration-effect relationships and represent mean inhibitor concentrations at which initial rates of uptake of 1 µM [3H]uridine were inhibited by 50% (see Fig. 2), and Ki (inhibitory constant) values were calculated using the Cheng-Prusoff equation (Cheng and Prusoff, 1973) as described in the Materials and Methods. Data are presented as means ± S.E.M. (n ≥ 3).
| Uridine | Adenosine | Tecadenoson | |||||||
|---|---|---|---|---|---|---|---|---|---|
| IC50 | Ki | IC50 | Ki | IC50 | Ki | ||||
| μM | n | μM | μM | n | μM | μM | n | μM | |
| hENT1 | 52 ± 5 | 4 | 51 ± 5 | 17 ± 1 | 3 | 12 ± 1 | 12 ± 1 | 4 | 11 ± 1 |
| hENT2 | 234 ± 22 | 6 | 242 ± 22 | 106 ± 5 | 3 | 106 ± 5 | 190 ± 21 | 3 | 189 ± 21 |
| hCNT1 | 5.8 ± 0.7 | 4 | 5.2 ± 0.6 | 2 ± 0.4 | 3 | 1.8 ± 0.4 | 41 ± 6 | 5 | 37 ± 5 |
| hCNT2 | 32 ± 4 | 5 | 31 ± 4 | 5.5 ± 1.6 | 3 | 5.3 ± 1.5 | 239 ± 3 | 4 | 231 ± 29 |
| hCNT3 | 5.4 ± 0.9 | 4 | 3.4 ± 0.6 | 3.3 ± 0.4 | 3 | 2.1 ± 0.3 | 200 ± 24 | 4 | 126 ± 18 |
CNT, concentrative nucleoside transporter; ENT, equilibrative nucleoside transporter; h, human.