Competition of [3H]DAMGO binding in cells stabling expressing mMOR-1 variants
[3H]DAMGO binding was performed in membranes from CHO cells stably transfected with the indicated variant constructs. Ki values were determined from at least three independent determinations of IC50 values (Cheng and Prusoff, 1973). Comparisons of the Ki values for each drug were then compared among the variants using A NOVA. Of the compounds, only DADLE (P < 0.0001), DSLET (P < 0.04), and endomorphin 2 (P < 0.01) showed significant differences. Tu key post hoc analysis for DADLE revealed that the Ki value for mMOR-1B1 differed significantly from mMOR-1, mMOR-1B3, and mMOR-1B5 (P < 0.001) as well as mMOR-1B2 (P < 0.05). With DSLET, mMOR-1B2 differed significantly from both mMOR-1B1 and mMOR-1B3 (P < 0.05), whereas mMOR-1B1 differed from both mMOR-1 and mMOR-1B3.
| Ligand | Ki Value | ANOVA | ||||
|---|---|---|---|---|---|---|
| mMOR-1 | mMOR-1B1 | mMOR-1B2 | mMOR-1B3 | mMOR-1B5 | ||
| nM | ||||||
| Morphine | 5.3 ± 2.0 | 5.3 ± 1.0 | 3.9 ± 0.4 | 1.5 ± 0.5 | 1.4 ± 0.6 | N.S. |
| M6G | 5.2 ± 1.8 | 10.1 ± 1.6 | 8.4 ± 1.3 | 3.9 ± 1.3 | 5.2 ± 0.1 | N.S. |
| DAMGO | 1.8 ± 0.5 | 1.4 ± 0.2 | 1.3 ± 0.1 | 1.8 ± 0.9 | 1.0 ± 0.3 | N.S. |
| DADLE | 2.1 ± 0.3 | 9.0 ± 1.1 | 4.9 ± 0.7 | 1.9 ± 0.4 | 2.4 ± 0.4 | P < 0.001 |
| DSLET | 12.5 ± 3.6 | 8.9 ± 1.1 | 22.1 ± 1.5 | 8.7 ± 1.8 | 11.5 ± 5.2 | P < 0.04 |
| Naloxone | 4.3 ± 0.9 | 0.5 ± 0.3 | 1.3 ± 0.1 | 1.4 ± 0.5 | 0.6 ± 0.3 | N.S. |
| Dynorphin A | 10.9 ± 0.5 | 14.6 ± 7.1 | 34.3 ± 18.4 | 8.7 ± 1.8 | 8.9 ± 2.3 | N.S. |
| β-Endorphin | 10.8 ± 2.9 | 6.8 ± 3.2 | 4.9 ± 1.7 | 3.1 ± 1.4 | 5.7 ± 1.2 | N.S. |
| Endomorphin 1 | 2.1 ± 0.8 | 10.8 ± 5.6 | 5.0 ± 1.8 | 3.2 ± 0.6 | 4.3 ± 0.8 | N.S. |
| Endomorphin 2 | 4.2 ± 1.8 | 12.4 ± 1.5 | 8.4 ± 1.1 | 3.2 ± 0.8 | 10.6 ± 1.8 | P < 0.01 |
| U50,488H | >500 | >500 | >500 | >500 | >500 | |
| DPDPE | >500 | >500 | >500 | >500 | >500 | |
N.S., not significant; DSLET, [D-Ser2, Leu5]enkephalin-Thr6.