Re. Rosenstein et Ml. Dubocovich, Characterization of 2-[I-125]-iodomelatonin binding sites in the golden hamster retina by autoradiography, BIOL RH RES, 32(2), 2001, pp. 191-200
The characterization of 2-[I-125]-iodomelatonin binding sites was performed
in the golden hamster retina using in vitro quantitative autoradiography.
The specific binding of the radioligand fulfills all the criteria for bindi
ng to a receptor site, being stable, reversible, saturable and of high affi
nity. 2-[I-125]-iodomelatonin labels a single class of sites in the section
s of whole eyes as well as in isolated retinas with a similar affinity, whe
reas the total number of receptors was higher in sections of whole eyes tha
n in isolated retinas. Melatonin and related analogues competed for 2-[I-12
5]-iodomelatonin binding with the following order of affinities: 2-iodomela
tonin > 6-hydroxymelatonin > melatonin > 6-chloromelatonin > > > N-acetyl-5
-hydroxytryptamine (NAS) > 5-methoxytryptamine > 5-hydroxytryptamine (serot
onin). Micromolar concentrations of GTP and GDP dose-dependently and specif
ically inhibited agonist binding, suggesting coupling of the binding sites
to a Gi protein. These results suggest the participation of melatonin in th
e regulation of retinal physiology trough activation of melatonin receptor
subtypes.