Melatonin binding sites in the brain of European sea bass (Dicentrarchus labrax).
Characteristics, day-night changes, guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) modulation, and localization of melatonin binding sites in the brain of a marine teleost, European sea bass Dicentrarchus labrax, were studied by radioreceptor assay using 2-[(125)I]iodomelatonin as a radioligand. The specific binding to the sea bass brain membranes was rapid, stable, saturable and reversible. The radioligand binds to a single class of receptor site with the affinity (Kd) of 9.3 +/-0.6 pM and total binding capacity (Bmax) of 39.08 +/-0.86 fmol/mg protein (mean+/-SEM, n=4) at mid-light under light-dark (LD) cycles of 12:12. Day-night changes were observed neither in the Kd nor in the Bmax under LD 12:12. Treatment with GTPgammaS significantly increased the Kd and decreased the Bmax both at mid-light and mid-dark. The binding sites were highly specific for 2-phenylmelatonin, 2-iodomelatonin, melatonin, and 6-chloromelatonin. Distribution of melatonin binding sites in the sea bass brain was uneven: The Bmax was determined to be highest in mesencephalic optic tectum-tegmentum and hypothalamus, intermediate in telencephalon, cerebellum-vestibulolateral lobe and medulla oblongata-spinal cord, and lowest in olfactory bulbs with the Kd in the low picomolar range. These results indicate that melatonin released from the pineal organ and/or retina plays neuromodulatory roles in the sea bass brain via G protein-coupled melatonin receptors.
Bayarri
María José
MJ
Department of Physiology and Pharmacology, Faculty of Biology, University of Murcia, 30100 Espinardo, Murcia, Spain.
Garcia-Allegue
Rosa
R
Muñoz-Cueto
José Antonio
JA
Madrid
Juan Antonio
JA
Tabata
Mitsuo
M
Sánchez-Vázquez
F Javier
FJ
Iigo
Masayuki
M
D000818:Animals; D001492:Bass / Q000378:metabolism* / Q000502:physiology; D001665:Binding Sites / Q000502:physiology; D001921:Brain / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D007457:Iodine Radioisotopes; D007700:Kinetics; D008550:Melatonin / Q000378:metabolism*; D017440:Photoperiod; D011869:Radioligand Assay
D007457:Iodine Radioisotopes; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D008550:Melatonin