Table 1. The effect of co-expression of GRK2 and subsequent treatment with β-funaltrexamine on the potency and intrinsic activity of µ-opioid receptor agonists in a β-arrestin recruitment assay.
| GFP | GFP | GRK2 | GRK2 | GRK2 | GRK2 | GRK2 | GRK2 | |
| Untreated pEC50±s.e.m (EC50 nM) | Emax | Untreated pEC50±s.e.m (EC50 nM) | Emax | β-fun 1 nM pEC50±s.e.m (EC50 nM) | % decrease in Emax comp to untreated | β-fun 10 nM pEC50±s.e.m (EC50 nM) | % decrease in Emax comp to untreated | |
| DAMGO | 6.16±0.14 (692) | 100% | 7.64±0.15A (22.9) | 100% | 7.50±0.16 (31.6) | 64±12 | 7.48±0.12 (33.1) | 36±4 |
| Pfizer comp 1 | 7.59±0.17 (25.7) | 106±4 | 9.04±0.10A (0.912) | 99±8 | 8.86±0.09 (1.38) | 71±9 | 8.65±0.16 (2.24) | 46±6 |
| Morphine | 6.08±0.09 (832) | 26±2 | 7.29±0.07A (51.2) | 98±5 | 7.12±0.02 (75.6) | 65±8 | 6.95±0.03 (112) | 42±6 |
| Oxycodone | 5.25±0.22 (5620) | 20±3 | 6.28±0.15A (525) | 95±4 | 6.18±0.12 (661) | 61±8 | 6.06±0.12 (871) | 39±3 |
| Endomorphin 1 | 6.87±0.18 (135) | 78±7 | 8.45±0.07A (3.55) | 76±9 | 8.16±0.09 (6.17) | 67±7 | 8.10±0.07 (7.94) | 36±1 |
| Endomorphin 2 | 6.56±0.11 (275) | 69±3 | 8.21±0.07A (6.17) | 74±4 | 8.05±0.12 (8.91) | 59±9 | 8.07±0.07 (8.51) | 31±3 |
Functional properties of agonists in the β-arrestin assay were determined as described in the experimental section. Potency values before and after treatment with β-funaltrexamine are expressed as pEC50±s.e.m (EC50 nM). Emax values before β-funaltrexamine treatment are expressed as % of the maximal response of DAMGO in U2OS µ-opioid receptor β-arrestin cells co-expressing either GFP or GRK2 (mean±s.e.m). The percentage reduction in Emax after treatment is expressed as a percentage of the agonist's Emax before treatment (mean±s.e.m). Data are from four independent experiments.
A
Values are significantly different from those determined in the absence of GRK2 (p<0.05, two-tailed t-test).