Table 1: Pharmacological characterization of naturally occurring δ-OR peptides.
Affinity of peptide agonists for the δ-OR is depicted as the pKi, which is a negative log value of the Ki, which is the concentration at which 50% of the δ-OR are occupied by the peptide. Potency and efficacy (α, normalized to leu-enkephalin) for the δ-OR peptide agonists to inhibit cAMP production is depicted as concentration of 50% inhibition (pIC50) and the SEM. Potency (pEC50) and efficacy (α, normalized to leu-enkephalin) of δ-OR agonists to recruit β-arrestin 1 and 2 are depicted with SEM. The number of repetitions for each drug is indicated in parentheses.
| Affinity | cAMP | β-arrestin1 | β-arrestin2 | ||||
|---|---|---|---|---|---|---|---|
| Compounds | pKi | pIC50 | α | pEC50 | α | pEC50 | α |
| Leu-enkephalin | 8.8±0.1 (4) | 9.0±0.1 (9) | 100 | 7.5±0.1 (11) | 100 | 7.5±0.1 (10) | 100 |
| Deltorphin II | 9.5±0.3 (5) | 9.4±0.1 (4) | 95±2 | 8.3±0.1 (5) | 94±6 | 8.7±0.2 (6) | 103±4 |
| Rubiscolin-5 | 5.5±0.1 (4) | 5.2±0.1 (6) | 85±9 | ND (9) | ND | 4.1±0.3 (7) | 15±4 |
| Rubsicolin-6 | 6.0±0.1 (3) | 5.8±0.2 (4) | 77±8 | ND (7) | ND | 5.1±0.3 (6) | 20±3 |