Coactivation of the 5-HT2A receptor with 5-HT and the MOP receptor with morphine results in desensitization to morphine
Cells treated with doxycycline (0.01 μg/ml) 24 h express 5-HT2A-eCFP. Cells were pretreated with either DAMGO or morphine for the indicated times, and membranes prepared from the cells were then used to assess the potency (top) and relative efficacy (bottom) of DAMGO or morphine to stimulate binding of [35S]GTPγS. Data are presented as pEC50 or percentage of maximal agonist effect (Emax). Desensitization was assessed by reduction in potency of the ligand following pretreatment. Numbers in parentheses indicate number of independent experiments. Values are presented as mean ± S.E.M.
Not Pretreated | 30 min | 60 min | 120 min | 240 min | Pretreatment | ||
|---|---|---|---|---|---|---|---|
| pEC50 | |||||||
| DAMGO | 8.03 ± 0.16 (5) | 7.23 ± 0.10 (5)* | 7.32 ± 0.06 (5)* | 7.07 ± 0.11 (5)* | 7.28 ± 0.10 (5)* | DAMGO 1 μM | |
| Morphine | 7.64 ± 0.11 (5) | 7.80 ± 0.08 (5) | 7.71 ± 0.11 (5) | 7.78 ± 0.14 (5) | 7.81 ± 0.18 (5) | Morphine 1 μM | |
| DAMGO | 8.00 ± 0.15 (5) | 8.13 ± 0.24 (5) | 7.92 ± 0.22 (5) | 7.96 ± 0.17 (5) | 8.03 ± 0.20 (5) | 5-HT 1 μM | |
| DAMGO | 7.64 ± 0.11 (5) | 8.07 ± 0.13 (5) | 8.20 ± 0.08 (5)* | 8.15 ± 0.07 (5)* | 8.14 ± 0.11 (5)* | 5-HT 1 μM | |
| DAMGO | 8.00 ± 0.02 (3) | 6.98 ± 0.14 (3)* | 7.15 ± 0.08 (3)* | 6.92 ± 0.31 (3)* | 6.99 ± 0.20 (3)* | DAMGO 1 μM | |
| 5-HT 1 μM | |||||||
| Morphine | 7.86 ± 0.14 (3) | 7.25 ± 0.10 (3)* | 7.24 ± 0.10 (3)* | 7.20 ± 0.18 (3)* | 7.22 ± 0.16 (3)* | Morphine 1 μM | |
| 5-HT 1 μM | |||||||
| % Not pretreated Emax | |||||||
| DAMGO | 100 (5) | 87.30 ± 5.53 (5) | 89.99 ± 4.00 (5) | 86.98 ± 3.90 (5) | 85.57 ± 3.05 (5) | DAMGO 1 μM | |
| Morphine | 100 (5) | 102.26 ± 2.06 (5) | 100.73 ± 1.84 (5) | 96.03 ± 5.66 (5) | 98.15 ± 3.80 (5) | Morphine 1 μM | |
| DAMGO | 100 (5) | 94.77 ± 3.42 (5) | 102.89 ± 3.15 (5) | 93.44 ± 3.37 (5) | 92.31 ± 4.71 (5) | 5-HT 1 μM | |
| Morphine | 100 (5) | 101.05 ± 2.43 (5) | 100.09 ± 6.72 (5) | 102.20 ± 7.69 (5) | 103.99 ± 5.71 (5) | 5-HT 1 μM | |
| DAMGO | 100 (3) | 96.27 ± 5.44 (3) | 90.88 ± 5.30 (3) | 74.73 ± 4.41 (3)* | 78.51 ± 1.74 (3)* | DAMGO 1 μM | |
| 5-HT 1 μM | |||||||
| Morphine | 100 (3)* | 79.37 ± 1.26 (3)* | 70.59 ± 3.01 (3)* | 64.10 ± 3.08 (3)* | 72.40 ± 3.15 (3)* | Morphine 1 μM | |
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| 5-HT 1 μM | |
↵* Different from not treated. P < 0.05 by Dunnett's post hoc test analysis of variance.