title: Effects of temperature on 2-[125I]-iodomelatonin binding to melatonin receptors in the neural retina of the frog Rana perezi.
abstract: The present study analyzes the effect of temperature-dependent modifications on the binding of the analog 2-[125I]-melatonin to melatonin receptors in isolated neural retina membranes from the greenfrog Rana perezi. Association and dissociation rate constants (K+1, K-1) were exponentially increased by the assay temperature. At 15 degrees C, association and dissociation required several hours; meanwhile, at 35 degrees C, rate constants were 100- and 34-fold faster, respectively. However, the Kd constant calculated as K-1/K+1 was unmodified by the assay temperature. When frogs were acclimated at either 5 or 22 degrees C for 1 month, K+1, and K-1 constants determined at 15 and 25 degrees C were identical in both cold- and warm-acclimated groups. Thus, the binding kinetics of melatonin receptors in frog retinas did not shown any thermal compensation. Results from saturation curves and pharmacological profiles of melatonin binding sites support a lack of effect of assay temperature on the affinity of melatonin receptors in the frog retina. The inhibition of [125I]Mel binding by GTPgammaS showed clearly that the coupling of melatonin receptors to G proteins is temperature-dependent. Higher concentrations of the GTP analog were needed to inhibit specific binding when temperature decreased. The temperature effect on binding kinetics and on the G protein coupling to melatonin receptors suggests that the melatonin signal could be transduced distinctly depending on the temperature. Thus, temperature plays a major role, not only on melatonin synthesis, but also in the transduction of melatonin signal in ectotherms.
authors.affiliation: Departamento de Fisiología (Fisiología Animal II), Facultad de Biología, Universidad Complutense, Madrid, España.
authors.forename: Esther
authors.initials: E
authors.lastname: Isorna
authors.forename: Ana
authors.initials: A
authors.lastname: Guijarro
authors.forename: Marcos A
authors.initials: MA
authors.lastname: López-Patiño
authors.forename: María Jesús
authors.initials: MJ
authors.lastname: Delgado
authors.forename: Mercedes
authors.initials: M
authors.lastname: Alonso-Bedate
authors.forename: Angel L
authors.initials: AL
authors.lastname: Alonso-Gómez
mesh_terms: D000064:Acclimatization; D000818:Animals; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008550:Melatonin / Q000031:analogs & derivatives* / Q000378:metabolism*; D011898:Ranidae / Q000378:metabolism*; D044094:Receptors, Melatonin / Q000378:metabolism*; D012160:Retina / Q000187:drug effects / Q000378:metabolism*; D012621:Seasons; D015398:Signal Transduction; D013696:Temperature
chemical_list: D044094:Receptors, Melatonin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C044556:2-iodomelatonin; D019204:GTP-Binding Proteins; D008550:Melatonin