Table of binding affinities and relative inverse agonist efficacies of drugs
| Drug | [3H]Yohimbine Binding | EC50 | [3H]cAMP | ||
|---|---|---|---|---|---|
| Ki | Relative Affinity CAM/WT (n) | Max[3H]cAMP Produced | |||
| WT | CAM | ||||
| nM | nM | % control | |||
| Epinephrine | 460 | 49 | 0.11 (3) | 7.7 | 370 |
| UK-14,304 | 55 | 7.6 | 0.14 (3) | 7.1 | 660 |
| Clonidine | 130 | 40 | 0.30 (3) | N.D. | N.D. |
| Rauwolscine | 5.3 | 11.2 | 2.1 (7) | 52 | 720 |
| Yohimbine | 5.6 | 8.3 | 1.5 (5) | 81 | 640 |
| RX821002 | 2.1 | 3.1 | 1.5 (5) | 160 | 480 |
| MK912 | 2.2 | 3.8 | 1.7 (4) | 87 | 360 |
| Phentolamine | 5.9 | 8.2 | 1.4 (3) | 1700 | 210 |
| Idazoxan | 18.0 | 18.3 | 1.0 (5) | —2-a | ≈100 |
| Phenoxybenzamine | >200 | >500 | N.D. (2) | —2-b | ≈100 |
| Prazosin | >10,000 | >10,000 | N.D. (2) | —2-b | ≈100 |
| Propranolol | >10,000 | >10,000 | N.D. (2) | —2-c | ≈100 |
K i values were calculated from IC50 values determined by competition binding for 10 nM [3H]yohimbine in the presence of 10 μM GppNHp (Fig. 2). Membranes were incubated for 30 min at room temperature in the presence of increasing concentrations of the indicated drugs. Relative affinities are the CAMK i divided by the WT K i for each drug. Data are from two to seven separate experiments performed in duplicate. EC50 values and maximum [3H]cAMP produced were determined from dose-response curves for the indicated drugs using whole cell adenylyl cyclase assays (Fig. 6). CAM cells were incubated for 30 min at 37°C in the presence of 1 mM IBMX, 30 μM forskolin, and increasing concentrations of the indicated drugs. Data are from three to seven separate experiments performed in duplicate except for phenoxybenzamine and prazosin, which are single experiments.