Table 1

Affinity and potency of melatonin at WT and epitope-tagged hMT1 and hMT2 melatonin receptors

Receptor Construct2-[125I]Iodomelatonin Binding (KD)Forskolin-Stimulated cAMP Accumulation
EC50Efficacy
nM nM %
WT MT1 0.15  ± 0.030.6  ± 0.389.1  ± 3.0
MT1 FLAG0.24  ± 0.021.7  ± 0.476.2  ± 7.0
MT1 FLAG/GFP0.18  ± 0.010.7  ± 0.351.5  ± 10.6
WT MT2 0.36  ± 0.061.4  ± 0.378.8  ± 2.5
MT2FLAG0.45  ± 0.095.0  ± 1.571.8  ± 10.3
MT2 FLAG/GFP0.33  ± 0.072.5  ± 0.960.7  ± 12.4

The affinity constants (KD) of 2-[125I]iodomelatonin binding to the WT, FLAG, and FLAG/GFP-tagged MT1 or MT2 receptors were determined using homologous competition with 2-iodomelatonin. The potency and efficacy of melatonin to inhibit forskolin-stimulated cAMP formation were determined in CHO cells stably expressing WT or FLAG-tagged or transiently expressing FLAG/GFP-tagged MT1or MT2 melatonin receptors. The potency of melatonin (0.1–1000 nM) was determined by nonlinear regression analysis and the maximal efficacy determined at a melatonin concentration of 100 nM. Values represent the mean ± S.E.M. of three to five independent experiments.

  • WT, wild-type.