Comparison of catecholamine transport kinetics for frog catecholamine (fET) and human norepinephrine transporter (hNET)
| Substrate | fET | hNET | ||||
|---|---|---|---|---|---|---|
| Km(nm) | Vmax (× 1018mol/ cell per min) | Vmax /Km (× 107 l/min) | Km(nm) | Vmax (× 1018mol/ cell per min) | Vmax /Km (× 107l/min) | |
| l-Epinephrine | 1527 ± 1521-a | 5.94 ± 0.97 | 3.87 ± 0.511-c | 2872 ± 24 | 3.16 ± 0.081-d | 0.90 ± 0.1 |
| l-Norepinephrine | 560 ± 92 | 5.45 ± 0.69 | 10.63 ± 2.2 | 737 ± 77 | 6.01 ± 0.23 | 8.4 ± 0.8 |
| Dopamine | 47 ± 91-a | 0.74 ± 0.071-b | 17.38 ± 3.31-c | 91 ± 6 | 3.55 ± 0.611-d | 38.9 ± 6.8 |
| l-Epi >l-NE >> DA | l-NE >l-Epi > DA | |||||
Transport of [3H]-l-epinephrine, [3H]-l-norepinephrine, and [3H]-dopamine were determined in HeLa cells transfected with expression vector containing either the fET or hNET cDNA, as described in Materials and Methods. Data are presented as mean ± SEM of three to four separate experiments. Statistical comparisons were performed using Student’s unpaired t test.
↵F1-a p < 0.05 as compared withKm of substrates tested on hNET.
↵F1-b p < 0.05 as compared withVmax of l-Epi and l-NE in fET.
↵F1-c p < 0.05 as compared withVmax /Km of substrates tested on hNET.
↵F1-d p < 0.05 as compared withVmax of l-NE in hNET.