TABLE 4

Binding affinities (Ki) measured in HEK 293 cells coexpressing MT1 and MT2 receptors and EC50 values of ligand-induced BRET for MT1/MT2 heterodimers

MT1-Rluc and MT2-YFP receptors were expressed at a 1:3 ratio (∼80 fmol/mg of protein) and 125I-MLT competition binding experiments and BRET measurements were performed as described under Materials and Methods and in Fig. 4. Data are means ± S.E. of at least three independent experiments each performed in triplicate.

Ligands Ki EC50Emax EC50 Ratio of MT2 Homodimer/Heterodimer
nM nM %
Melatonin 0.40 ± 0.16 16.8 ± 9.7 142 ± 9 1.5
S20098 0.23 ± 0.17 7.7 ± 4.6 136 ± 6 1.8
S22153 8.87 ± 2.34 6.4 ± 5.6 132 ± 10 7.3
S20928 116.6 ± 1.75 14 ± 9.5 136 ± 7 26.3
4P-PDOT 8.60 ± 7.40 211 ± 159 141 ± 4 0.2
Luzindole 32.4 ± 9.20 1.0 ± 0.1 134 ± 13 126
S24773 4.5 ± 1.0 4.1 ± 2.2 137 ± 4 8