Characterization of melatonin binding sites in chicken and human intestines.
The radioligand 2-[125I]iodomelatonin was used to study melatonin binding sites in chicken and human intestines. In the chicken duodenum, 2-[125I]iodomelatonin binding sites were enriched in the musculosa layer (Bmax approximately 1 fmol/mg protein) as compared to the mucosa/submucosa layer (Bmax approximately 0.2 fmol/mg protein). 2-[125I]iodomelatonin bound with a Kd of 68 +/- 18 pM (mean +/- S.E.M., n = 13) and was displaced by melatonin with a Ki of 0.3 nM. The Kd value for 2-[125I]iodomelatonin was increased 2- to 4-fold by a GTP analog, suggesting that the binding sites might be coupled to a G-protein. The affinity order of nine melatonin analogs at the enteric binding sites was in agreement with the pharmacological profile of melatonin receptors described in other tissues. In the human jejunum, 2-[125I]iodomelatonin binding could be observed in the mucosa/submucosa layer (Kd = 150-200 pM, Bmax = 0.7 fmol/mg protein). The radioligand was efficiently displaced by melatonin (Ki = 0.6 nM) but only marginally by N-acetyltryptamine (Ki = 22 microM) and serotonin (Ki = 14 microM).
Pontoire
C
C
Laboratoire de Neuroendocrinologie Cellulaire, URA CNRS 290, France.
Bernard
M
M
Silvain
C
C
Collin
J P
JP
Voisin
P
P
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002645:Chickens; D004386:Duodenum / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives / Q000378:metabolism; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D008875:Middle Aged; D011402:Pronase; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D044094:Receptors, Melatonin
D006150:Guanine Nucleotides; D007457:Iodine Radioisotopes; D011956:Receptors, Cell Surface; D044094:Receptors, Melatonin; C044556:2-iodomelatonin; D011402:Pronase; D019204:GTP-Binding Proteins; D008550:Melatonin