Effect of cocaine on kinetic parameters determined from saturation analysis of the initial rate ofm-tyramine-induced dopamine efflux
| Dopamine | m-Tyramine | ||||
|---|---|---|---|---|---|
| [Cocaine] (μm) | Km obs(μm) | Vmax obs(pmol/sec/mg) | [Cocaine] (μm) | Km obs (μm) | Vmax obs(pmol/sec/mg) |
| 0 | 364 ± 31 | 23 ± 3 | 0 | 2.0 ± 0.5 | 7.8 ± 0.8 |
| 3 | 356 ± 47 | 18 ± 3 | 3 | 4.8 ± 0.9* | 7.4 ± 0.8 |
| 10 | 378 ± 35 | 13 ± 1** | 6 | 6.7 ± 0.7** | 7.0 ± 0.8 |
| 30 | 401 ± 81 | 8 ± 2** | 10 | 10.6 ± 1.2** | 7.2 ± 1.0 |
m-Tyramine (10 μm) and cocaine were added at the same time. For DA dependence, the DA efflux was initiated by 10 μmm-tyramine at various concentrations of intracellular DA (44–321 μm). Form-tyramine dependence, the DA efflux was initiated by various concentrations of m-tyramine (1–100 μm) at 84 μm [DA]i. The competitive Ki of cocaine in the latter experiment was 2.36 ± 0.43 μm, estimated as described in Table 1. The values are means ± SE of three independent experiments.
*p < 0.05.
**p < 0.01 vs [cocaine] = 0 (Newman–Keuls test).