To determine the affinity of
new opioid receptor ligands to cloned μ opioid receptors stably expressed in CHO cell and measurement
of the ligands inhibition of intracellular cAMP level. The binding characteristics of the opioid ligand diprenorphine were studied by radioligands binding in cloned δ opioid receptors stably expressed in Chinese hamster ovary cells in saturation binding experiments, and then followed by competition binding experiments with a variety of
new opioid receptor ligands A, B, C, D, E, F, G, DAMGO (
enkephalin and Morphine. The opioid ligands inhibition of intracellular cAMP production was determined. diprenorphine bound to a larger population of mu receptors (Kd, 1.06; Bmax 930 fmol/mg protein ). Competition binding experiments revealed that IC 50 values of the new ligands, DAMGO and Morphine were 13.33 ±3.73, 14.36 ±1.58, 0.62 ±0.03, 56.38±2.33, 65.72±26.44, 33.10±11.33, 0.55±0.06, 3.69±1.59 and 1.83±0.50 respectively. Ligand C, G displayed much higher affinity than DAMGO and Morphine( P <0.05). However, the affinity of ligand A, B,D, E,F were lower than that of DAMGO and Morphine. IC 50 values of the new ligands, that of DAMGO and Morphine in inhibiting forskolin-stimulated production of intracellular cAMP were 6.49 ±1.59, 1390 ±61.10, 0.84 ±0.11, 2.33±1.24, 25.00±17.20, 1.42±1.21, 0.01±0.01, 0.10±0.05 and 0.04±0.01 respectively. Ligand G possesses the highest potency in inhibiting forsklin stimulated conversion to cAMP, higher than Morphine. Ligand A,C,D and E were similar to DAMGO and Morphine. The results suggest that the new ligands have good affinity to μ opioid receptors and inhibit intracellular cAMP production.