Table 3.
Kinetic parameters for substrates transported by OCT3 and its nonsynonymous variants
| A | ||||
|---|---|---|---|---|
| Substrates | OCT3-Ref (Km/Vmax) | T44M (Km/Vmax) | T400I (Km/Vmax) | V423F (Km/Vmax) |
| MPP+ | 85 ± 10 /1783 ± 98 | 94 ± 16 / 2126 ± 162* | 65 ± 18 / 1865 ± 125 | 62 ± 13 / 1914 ± 125 |
| Tyramine | 281 ± 36 / 641± 61 | 242 ± 62 / 628± 85 | 303 ± 87 / 592 ± 43 | 259± 53 / 574± 82 |
| Histamine | 131 ± 57 / 1498± 104 | 164 ± 174 / 1822 ± 113* | 115± 26 / 1469 ± 164 | 129 ± 26 / 1413 ± 114 |
| Serotonin | 236 ± 31 / 889 ± 69 | 252 ± 51 / 964 ± 128 | 219 ± 21 / 997 ± 107 | 195 ± 21 / 843 ± 92 |
| Dopamine | 443± 56 / 658 ± 152 | 456 ± 140 / 507 ± 22 | 1292 ± 54* / 572 ± 44 | 1037 ± 83* / 472 ± 61 |
| Norepinephrine | 305 ± 42 / 1051 ± 183 | 445 ± 111 / 965 ± 65 | 908 ± 138* / 1080 ± 87 | 832 ± 138* / 1027 ± 103 |
| Epinephrine | 480 ± 65 / 597 ± 72 | 397 ± 85 / 507 ± 41 | 850 ± 110 */ 541 ± 56 | 712 ± 153* / 518 ± 53 |
| B | |||||||
|---|---|---|---|---|---|---|---|
| Kinetic parameter | OCT3-Ref. | T44M | A116S | L186F | V388M | T400I | V423F |
| Vmax (nmol/mg protein/min) | 4.72 ± 0.54 | 6.43 ± 0.39 * | 4.36 ± 0.37 | 4.56 ± 0.73 | 4.94 ± 0.47 | 3.36 ± 0.54 | 3.52 ± 0.53 |
| Km(mM) | 1.09 ± 0.21 | 1.15 ± 0.43 | 1.02 ± 0.23 | 1.04 ± 0.15 | 1.13 ± 0.36 | 3.81 ± 0.42* | 2.95 ± 0.21* |
For the kinetic studies, uptake rates were determined at 1 minute except metformin which was determined at 5 minutes. OCT3-Ref., OCT3-reference;
*
p <0.05 versus the reference. Values represent the mean ± SD calculated from 3 separate experiments and experiment was performed in triplicate. A, Kinetic parameters of MPP+ and monoamines by reference OCT3 and its nonsynonymous variants. The unit of Vmax, pmol/mg protein/min; the unit of Km, nM; B, Kinetic parameters of metformin of OCT3 and its variants.