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Specific binding of 2‐[ 125 I]iodomelatonin by rat spleen crude membranes: Day‐night variations and effect of pinealectomy and continuous light exposure
Author(s) -
RafiiEIldrissi Mohammed,
Calvo Juan R.,
Giordano Mirta,
Guerrero Juan M.
Publication year - 1996
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1996.tb00236.x
Subject(s) - pinealectomy , melatonin , binding site , membrane , melatonin receptor , binding constant , biology , spleen , medicine , ligand binding assay , endocrinology , chemistry , biochemistry , receptor , pineal gland , immunology
Melatonin binding sites were characterized in rat spleen crude membranes. The specific binding of 2‐[ 125 I]iodomelatonin by spleen crude membranes fulfills all the criteria for binding to a receptor site. Thus, binding was dependent on time and temperature, stable, specific, and increased under constant light exposure and after pinealectomy. In competition studies, the specific binding of 2‐[ 125 I]iodomelatonin to spleen crude membranes was inhibited by increasing concentrations of native melatonin. Scatchard analysis showed that the data were compatible with the existence of two classes of binding sites: a high affinity site with a K d of 0.53 nM and a binding capacity of 2.52 pM, and a low‐affinity site with a K d of 374 nM and binding capacity of 820 pM. Moreover, binding of 2‐[ l25 I]iodomelatonin exhibited day‐night variations with the highest binding observed late during the light period, and the lowest binding was observed late at night. However, binding of 2‐[ 125 I]iodomelatonin to membranes remained high when animals were kept under light exposure at night. Results support the hypothesis of a regulatory role of melatonin on the immune system in which melatonin downregulates its own binding site.