Agonist (10−6M) pretreatment (3 hr) effects on opioid inhibition of forskolin-stimulated cAMP levels for mu-TRUNC mutant opioid receptor expressed in HEK 293 cells
| Ligand | μ-TRUNC Untreated Cells | μ-TRUNC Agonist Pretreated Cells | ||
|---|---|---|---|---|
| EC50 (nM) | Max. inhibition (%) | EC50(nM) | Max. inhibition (%) | |
| Fentanyl | 0.53 ± 0.14 | 87.3 ± 0.3 | 9.8 ± 1.34-a | 91.3 ± 0.34-a |
| Lofentanil | 0.08 ± 0.1 | 84.7 ± 2.1 | 36.9 ± 12.24-b | 18.0 ± 6.84-c |
| Sufentanil | 0.002 ± 0.001 | 81.7 ± 2.6 | 10.7 ± 2.24-a | 27.3 ± 2.74-c |
| Nalbuphine | 14.4 ± 3.0 | 42.7 ± 6.4 | 8.3 ± 1.3 | 48.3 ± 5.2 |
Effects of agonist pretreatment on opioid inhibition of cAMP accumulation for the mu-TRUNC mutant receptor. HEK 293 cell monolayers were either untreated (control) or treated (pretreated) for 3 hr at 37°C with 1 μM of appropriate ligand (fentanyl, lofentanil, sufentanil or nalbuphine). After 30 min incubation with 0.5 mM IBMX at 37°C, cells were then incubated with 10 μM forskolin and 1 μM of appropriate ligand for 5 min at 37°C and then assayed for intracellular cAMP levels as described in “Methods.” Both treated and untreated results represent the mean ± S.E. of at least three separate experiments, each performed and assayed in duplicate. Statistical significance (P < .05) was determined by a paired Student’s t test.
↵4-a P < .01 (Student’s t test, compared to untreated).
↵4-b P < .05.
↵4-c P < .001.