The potency and efficacy of ligands at D2L receptor-G protein fusions
[35S]GTPγS binding studies were performed, as described under Materials and Methods, on membranes of HEK293T cells transfected to transiently express each of the fusion proteins. Estimates of pEC50 for each ligand as well as agonist efficacy measurements relative to dopamine (± S.E.M.) are provided. %DA, Emax value of [35S]GTPγS binding compared with maximal dopamine stimulation. The values of potency or efficacy for each ligand at the four different D2L-fusion proteins were compared using one-way ANOVA with a Bonferroni post-test using Prism version 4 (GraphPad Software Inc.). A significant difference was observed in pEC50 between D2L receptor fusion proteins for dopamine: D2LGαo1 > D2LGα i1 = D2LGα i3 = D2LGα i2 (p < 0.05).
D2LGαi1 | D2L Gαi2 | D2L Gαi3 | D2L Gαo1 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| pEC50 (±S.E.M.) | Emax | pEC50 (±S.E.M.) | Emax | pEC50 (±S.E.M.) | Emax | pEC50 (±S.E.M.) | Emax | |||||
| %DA (±S.E.M.) | %DA (±S.E.M.) | %DA (±S.E.M.) | %DA (±S.E.M.) | |||||||||
| Dopamine | 5.6 (0.05) | 100 | 5.3 (0.15) | 100 | 4.9 (0.15) | 100 | 6.2 (0.15) | 100 | ||||
| m-Tyramine | 4.8 (0.14) | 50 (2) | 4.9 (0.32) | 40 (13) | 4.9 (0.30) | 34 (2) | 5.4 (0.03) | 74 (3) | ||||
| p-Tyramine | N.A. | N.A. | N.A. | 3.9 (0.20) | 53 (4) | |||||||
| R-(+)-3-PPP | 4.8 (0.06) | 61 (2) | 4.7 (0.30) | 33 (2) | 4.6 (0.23) | 41 (10) | 5.2 (0.02) | 82 (1) | ||||
| S-(-)-3-PPP | N.A. | N.A. | N.A. | 6.3 (0.09) | 21 (2) | |||||||
| Quinpirole | 5.5 (0.06) | 99 (1) | 4.7 (0.76) | 59 (27) | 5.6 (0.42) | 55 (15) | 6.1 (0.03) | 100 (4) | ||||
| NPA | 7.8 (0.45) | 140 (6) | 7.6 (0.23) | 96 (18) | 7.5 (0.31) | 100 (17) | 7.9 (0.58) | 110 (5) | ||||
| 7-OH-DPAT | 8.1 (0.13) | 34 (1) | N.A. |
| 7.8 (0.30) | 21 (2) | 8.0 (0.21) | 51 (1) | ||||
N.A., no detectable stimulation.