Relative potencies of various opioid agonists to inhibit forskolin-stimulated production of intracellular cAMP in HEK293 cells expressing the wild-type and third intracellular loop deletion mutant μ-opioid receptors
| The ability of various concentrations of DAMGO, morphine, or PL017 to inhibit 10 μM forskolin-stimulated intracellular cAMP production in HEK293 cells stably expressing the wild-type and the third intracellular loop deletion mutant μ-opioid receptor was determined as described under Materials and Methods. K1 represents the concentration of agonist that produced 50% of the maximal inhibition. Data represent mean ± S.E.M. of two (when minimal inhibition was observed) to eight separate dose response experiments in triplicates. | ||||||||||||||||||
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| Receptor | DAMGO | Morphine | PL017 | |||||||||||||||
| KI | Max. Inh. | KI/KH | KI | Max. Inh. % | KI/KH | KI | Max. Inh. | KI/KH | ||||||||||
| nM | % | nM | % | nM | % | |||||||||||||
| WT | 8.3 ± 2.6 | 87 ± 2 | 5.9 | 13 ± 2.8 | 85 ± 2 | 5.3 | 11 ± 2.1 | 85 ± 2 | 1.0 | |||||||||
| i3-1 | >10,000 | >10,000 | >10,000 | |||||||||||||||
| i3-2 | 6.4 ± 1.3 | 72 ± 3 | 2.8 | 83 ± 43 | 49 ± 6* | 14 | 120 ± 21* | 67 ± 8* | 15 | |||||||||
| i3-3 | 5.6 ± 2.4 | 73 ± 5 | 5.1 | 6.0 ± 2.1* | 75 ± 2 | 6.5 | 1.8 ± 0.4* | 82 ± 4 | 0.12 | |||||||||
| i3-4 | 12 ± 5.3 | 72 ± 4 | 45 | 29 ± 12 | 80 ± 2 | 11 | 13 ± 4.9 | 84 ± 3 | 5.4 | |||||||||
| i3-5 | >10,000 | >10,000 | >10,00 | |||||||||||||||
| 5A | >10,000 |
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| >10,000 |
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| >10,000 |
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WT, wild-type.
↵* Signifies statistical significant differences (p < 0.05) as determined by comparing the values of the mutant receptors to that of wild-type receptor using student unpaired t test.