title: Receptor-mediated modulation of avian caecal muscle contraction by melatonin: role of tyrosine protein kinase.
abstract: Abstract: Melatonin receptors in the quail caecum were studied by 2[125I]iodomelatonin binding assay and the involvement of tyrosine protein kinase in the melatonin-induced contraction was explored. The binding of 2[125I]iodomelatonin in the quail caecum membrane preparations was saturable, reversible and of high affinity with an equilibrium dissociation constant (Kd) of 24.6 +/- 1.1 pm (n = 7) and a maximum number of binding sites (Bmax) of 1.95 +/- 0.09 fmol (mg/protein) (n = 7). The relative order of potency of indoles in competing for 2[125I]iodomelatonin binding was: 2-iodomelatonin > melatonin > 2-phenylmelatonin > 6-chloromelatonin > 6-hydroxymelatonin > N-acetylserotonin, indicating that ML(1) receptors are involved. The binding was inhibited by Mel1b melatonin receptor antagonists, luzindole and 4-phenyl-2-propionamidotetralin (4-P-PDOT) as well as by non-hydrolyzable analogs of GTP like GTPgammaS and Gpp(NH)p but not by adenosine nucleotides. The latter suggests that the action of melatonin on the caecum is G-protein linked. Cumulative addition of melatonin (1-300 nM) potentiated both the amplitude and frequency of spontaneous contractions in the quail caecum. The potentiation of rhythmic contractions was blocked by both luzindole and 4-P-PDOT. Antagonists of tyrosine kinase, genistein(2 microM) and erbstatin(4 microM) suppressed the modulation of spontaneous contractions by melatonin, but not inhibitors of protein kinase C (PKC) or protein kinase A (PKA). Melatonin-induced increment in spontaneous contraction was blocked by nifedipine (0.4 nM). Thus, we suggest that melatonin potentiates spontaneous contraction in the quail caecum via interacting with G-protein-coupled Mel(1b) receptor which may activate L-type Ca2+ channels by mobilizing tyrosine kinases.
authors.affiliation: Department of Physiology, Faculty of Medicine, The University of Hong Kong, China. amspoon@hkucc.hku.hk
authors.forename: A M S
authors.initials: AM
authors.lastname: Poon
authors.forename: G M
authors.initials: GM
authors.lastname: Kravtsov
authors.forename: S F
authors.initials: SF
authors.lastname: Pang
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001667:Binding, Competitive; D002432:Cecum / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D007211:Indoles / Q000378:metabolism; D008550:Melatonin / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism; D009281:Naphthalenes / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011784:Quail; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D044094:Receptors, Melatonin; D013764:Tetrahydronaphthalenes / Q000494:pharmacology; D014363:Tryptamines / Q000494:pharmacology
chemical_list: C114459:4-phenyl-2-propionamidotetraline; D004791:Enzyme Inhibitors; D007211:Indoles; D009281:Naphthalenes; D015221:Potassium Channels; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; D013764:Tetrahydronaphthalenes; D014363:Tryptamines; C057154:luzindole; D001030:Apamin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D006160:Guanosine Triphosphate; C044556:2-iodomelatonin; D011505:Protein-Tyrosine Kinases; C058819:calphostin C; D008550:Melatonin