Table 2. Inhibition constants for different agonists at the cloned guinea pig mu opioid receptor.
| Agonist | Ki[nM] |
|---|---|
| DAMGO | 3.4±0.6 |
| U50,488 | 930±90 |
| DPDPE | 3300±500 |
|
| |
| Methadone | 7.2±1.1 |
| (−)-Methadone | 3.4±0.9 |
| (+)-Methadone | 105±30 |
|
| |
| Morphine | 5.5±0.5 |
| Morphine-6-β-D-glucuronide | 30±6 |
| Morphine-3-β-D-glucuronide | 560±50 |
|
| |
| Levorphanol | 1.2±0.2 |
| Dextrorphan | 1740±360 |
Competition binding was performed with CHO membrane preparations. The Ki values reflect the potency of each unlabeled competitor to displace 0.3 nM [3H]-diprenorphine. One site analysis was the best fit model for all compounds tested. Non-specific (NSB) and total binding (TB) was determined in the absence of competitor. Data are mean ± S.E.M of three separate experiments conducted in triplicates.