Pharmacological characterization of human recombinant melatonin mt(1) and MT(2) receptors

Br J Pharmacol. 2000 Mar;129(5):877-86. doi: 10.1038/sj.bjp.0703130.


We have pharmacologically characterized recombinant human mt(1) and MT(2) receptors, stably expressed in Chinese hamster ovary cells (CHO-mt(1) and CHO-MT(2)), by measurement of [(3)H]-melatonin binding and forskolin-stimulated cyclic AMP (cAMP) production. [3H]-melatonin bound to mt(1) and MT(2) receptors with pK(D) values of 9.89 and 9.56 and B(max) values of 1.20 and 0.82 pmol mg(-1) protein, respectively. Whilst most melatonin receptor agonists had similar affinities for mt(1) and MT(2) receptors, a number of putative antagonists had substantially higher affinities for MT(2) receptors, including luzindole (11 fold), GR128107 (23 fold) and 4-P-PDOT (61 fold). In both CHO-mt(1) and CHO-MT(2) cells, melatonin inhibited forskolin-stimulated accumulation of cyclic AMP in a concentration-dependent manner (pIC(50) 9.53 and 9.74, respectively) causing 83 and 64% inhibition of cyclic AMP production at 100 nM, respectively. The potencies of a range of melatonin receptor agonists were determined. At MT(2) receptors, melatonin, 2-iodomelatonin and 6-chloromelatonin were essentially equipotent, whilst at the mt(1) receptor these agonists gave the rank order of potency of 2-iodomelatonin>melatonin>6-chloromelatonin. In both CHO-mt(1) and CHO-MT(2) cells, melatonin-induced inhibition of forskolin-stimulated cyclic AMP production was antagonized in a concentration-dependent manner by the melatonin receptor antagonist luzindole, with pA(2) values of 5.75 and 7.64, respectively. Melatonin-mediated responses were abolished by pre-treatment of cells with pertussis toxin, consistent with activation of G(i)/G(o) G-proteins. This is the first report of the use of [(3)H]-melatonin for the characterization of recombinant mt(1) and MT(2) receptors. Our results demonstrate that these receptor subtypes have distinct pharmacological profiles.

MeSH terms

  • Animals
  • Binding, Competitive / drug effects
  • CHO Cells
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Colforsin / antagonists & inhibitors
  • Colforsin / pharmacology
  • Cricetinae
  • Cyclic AMP / biosynthesis
  • Humans
  • Isotope Labeling
  • Kinetics
  • Melatonin / analogs & derivatives
  • Melatonin / metabolism
  • Pertussis Toxin
  • Radioligand Assay
  • Receptors, Cell Surface / agonists
  • Receptors, Cell Surface / antagonists & inhibitors
  • Receptors, Cell Surface / metabolism*
  • Receptors, Cytoplasmic and Nuclear / agonists
  • Receptors, Cytoplasmic and Nuclear / antagonists & inhibitors
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Receptors, Melatonin
  • Recombinant Proteins
  • Virulence Factors, Bordetella / pharmacology


  • Receptors, Cell Surface
  • Receptors, Cytoplasmic and Nuclear
  • Receptors, Melatonin
  • Recombinant Proteins
  • Virulence Factors, Bordetella
  • Colforsin
  • 2-iodomelatonin
  • Cyclic AMP
  • Pertussis Toxin
  • Melatonin