Day-night specific binding of 2-[125I]Iodomelatonin and melatonin content in gill, small intestine and kidney of three fish species

Ewa Kulczykowska, Hanna Kalamarz, Justin M. Warne, Richard J. Balment

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Some of melatonin's (Mel) well-established physiological effects are mediated via high-affinity cell-membrane receptors belonging to the superfamily of G-protein-coupled receptors. Specific binding of ligand 2-[ 125I]iodomelatonin, using membrane preparations from osmoregulatory tissues of flounder, rainbow trout and sea bream, together with Mel concentrations in the tissues and plasma were studied. The kidney, gill and small intestine samples were collected during the day and at night. The dissociation constants (Kd) and maximal binding densities (B max) were calculated for each tissue at 11:00 and 23:00 h. The binding sites with Kd values in the tissues in the picomolar range indicated the high affinity. Kd and Bmax values were tissue- and species-dependent. The GTP analogue [Guanosine 5′-O-(3- thiotriphosphate)] treatment significantly reduced the Bmax value, indicating that the 2-[125I]iodomelatonin-binding sites are probably coupled to a G-protein. No daily variations in Kd and Bmax values were observed. These are the first studies of the presence of 2-[ 125I]iodomelatonin-binding sites in the small intestine, kidney tubule and gill of fish. The data strongly suggest new potential targets for Mel action and the influence of Mel on water/ion balance in fish. The intestine seems to be a site of Mel synthesis and/or an active accumulation of the hormone. © Springer-Verlag 2005.
    Original languageEnglish
    Pages (from-to)277-285
    Number of pages8
    JournalJournal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology
    Volume176
    Issue number4
    DOIs
    Publication statusPublished - May 2006

    Keywords

    • Fish [125I]Iodomelatonin binding
    • Melatonin
    • Osmoregulation
    • Osmoregulatory tissues

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