Specific binding of 2-[125I]iodomelatonin by rat spleen crude membranes: Day-night variations and effect of pinealectomy and continuous light exposure

Authors

  • Mohammed Rafii-EI-ldrissi,

    1. Department of Medical Biochemistry and Molecular Biology, The University of Seville School of Medicine and Virgen Hospital, Seville, Spain
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  • Juan R. Calvo,

    1. Department of Medical Biochemistry and Molecular Biology, The University of Seville School of Medicine and Virgen Hospital, Seville, Spain
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  • Mirta Giordano,

    1. Laboratory of Immunology, Institute of Hematologic Research, National Academy of Medicine, Buenos Aires, Argentina
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  • Juan M. Guerrero

    Corresponding author
    1. Department of Medical Biochemistry and Molecular Biology, The University of Seville School of Medicine and Virgen Hospital, Seville, Spain
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Address reprint requests to Juan M. Guerrero, The University of Seville School, of Medicine, Department of Medical Biochemistry and Molecular Biology, Avda Sanchez Pizjuan 4, 41009-Seville, Spain.

Abstract

Abstract: Melatonin binding sites were characterized in rat spleen crude membranes. The specific binding of 2-[125I]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-[125I]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 Kd of 0.53 nM and a binding capacity of 2.52 pM, and a low-affinity site with a Kd of 374 nM and binding capacity of 820 pM. Moreover, binding of 2-[l25I]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-[125I]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.

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