Characterisation of melatonin binding sites in the eye of the Japanese quail (Coturnix japonica).
Melatonin binding sites were examined in the quail eye using 2-[125]iodomelatonin. Radioreceptor assays indicated similar binding sites in membrane preparations of neural retina (NR) and choroid-retinal pigment epithelium (C-RPE) eye components. In both tissues binding of the radioligand was specific, saturable, and of high affinity [Kd values NR 50.8 +/- 19.5 pM, C-RPE 98.2 +/- 35.4 pM, mean +/- SEM (n = 4)] and low capacity (Bmax values NR 12.4 +/- 2.7 fmol/mg protein, C-RPE 21.5 +/- 3.2 fmol/mg protein). Kinetic studies demonstrated that association of 2-[125I]iodomelatonin was rapid and further that this binding was reversible upon the addition of 1 microM melatonin. The order of pharmacological potencies of various indoles tested in 2-[125I]iodomelatonin displacement studies was melatonin > 6-chloromelatonin > 6-hydroxymelatonin > N-acetylserotonin >> 5-methoxytryptophol > 5-hydroxytryptamine > 5-methoxytryptamine (5-hydroxytryptamine > 5-methoxytryptophol for C-RPE). Studies with guanine nucleotides indicated that the signal transduction mechanism of the binding site may involve a G-protein linkage. This melatonin binding site displays several pharmacological similarities with those investigated in the retina of other species and with those previously characterised in the quail brain.
James
K
K
School of Biological Sciences, University of Surrey, Guildford, United Kingdom.
Skene
D J
DJ
Lucini
V
V
Stankov
B
B
Arendt
J
J
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002829:Choroid / Q000187:drug effects / Q000378:metabolism*; D003370:Coturnix; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives / Q000378:metabolism*; D009711:Nucleotides / Q000494:pharmacology; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D011869:Radioligand Assay; D011956:Receptors, Cell Surface / Q000378:metabolism*; D044094:Receptors, Melatonin; D012160:Retina / Q000378:metabolism*
D007211:Indoles; D007457:Iodine Radioisotopes; D009711:Nucleotides; D011956:Receptors, Cell Surface; D044094:Receptors, Melatonin; D008550:Melatonin