title: Molecular cloning and pharmacological characterization of rat melatonin MT1 and MT2 receptors.
abstract: In order to interpret the effects of melatonin ligands in rats, we need to determine their activity at the receptor subtype level in the corresponding species. Thus, the rat melatonin rMT(1) receptor was cloned using DNA fragments for exon 1 and 2 amplified from rat genomic DNA followed by screening of a rat genomic library for the full length exon sequences. The rat rMT(2) receptor subtype was cloned in a similar manner with the exception of exon 1 which was identified by screening a rat genomic library with exon 1 of the human hMT(2) receptor. The coding region of these receptors translates proteins of 353 and 364 amino acids, respectively, for rMT(1) and rMT(2). A 55% homology was observed between both rat isoforms. The entire contiguous rat MT(1) and MT(2) receptor coding sequences were cloned, stably expressed in CHO cells and characterized in binding assay using 2-[(125)I]-Iodomelatonin. The dissociation constants (K(d)) for rMT(1) and rMT(2) were 42 and 130 pM, respectively. Chemically diverse compounds previously characterized at human MT(1) and MT(2) receptors were evaluated at rMT(1) and rMT(2) receptors, for their binding affinity and functionality in [(35)S]-GTPgammaS binding assay. Some, but not all, compounds shared a similar binding affinity and functionality at both rat and human corresponding subtypes. A different pharmacological profile of the MT(1) subtype has also been observed previously between human and ovine species. These in vitro results obtained with the rat melatonin receptors are thus of importance to understand the physiological roles of each subtype in animal models.
authors.affiliation: Division de Pharmacologie Moléculaire et Cellulaire, Institut de Recherches Servier, 125 chemin de Ronde, 78290 Croissy-sur-Seine, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Audinot
authors.forename: Anne
authors.initials: A
authors.lastname: Bonnaud
authors.forename: Line
authors.initials: L
authors.lastname: Grandcolas
authors.forename: Marianne
authors.initials: M
authors.lastname: Rodriguez
authors.forename: Nadine
authors.initials: N
authors.lastname: Nagel
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Galizzi
authors.forename: Ales
authors.initials: A
authors.lastname: Balik
authors.forename: Sophie
authors.initials: S
authors.lastname: Messager
authors.forename: David G
authors.initials: DG
authors.lastname: Hazlerigg
authors.forename: Perry
authors.initials: P
authors.lastname: Barrett
authors.forename: Philippe
authors.initials: P
authors.lastname: Delagrange
authors.forename: Jean A
authors.initials: JA
authors.lastname: Boutin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D003001:Cloning, Molecular; D006224:Cricetinae; D003412:Cricetulus; D005091:Exons / Q000235:genetics; D006801:Humans; D008550:Melatonin / Q000031:analogs & derivatives / Q000378:metabolism; D008969:Molecular Sequence Data; D051381:Rats; D044122:Receptor, Melatonin, MT1 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D044123:Receptor, Melatonin, MT2 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D017422:Sequence Analysis, DNA
chemical_list: D044122:Receptor, Melatonin, MT1; D044123:Receptor, Melatonin, MT2; C044556:2-iodomelatonin; D008550:Melatonin