High affinity specific binding of 2-[125I]iodomelatonin by spleen membrane preparations of chicken.
The binding sites for 2-[125I]iodomelatonin in chicken spleens were characterized. The binding was rapid, stable, saturable, reversible, and of high affinity. Both melatonin and 6-chloromelatonin strongly inhibited the binding. The dissociation constant (Kd) obtained from the Scatchard analysis was 31.4 +/- 5.19 pmol/l (3-weeks old, n = 4), which was in good agreement with the Kd (50.6 pmol/l) calculated from the kinetic study. The maximum number of binding sites (Bmax) was 1.09 +/- 0.11 fmol/mg protein (3-weeks old, n = 4). Twelve 11-week-old chicks were killed in two groups at mid-light or mid-dark. Saturation studies indicated no significant difference (P greater than 0.05) in the Kd between mid-light (42.1 +/- 3.9 pmol/l) and mid-dark (31.6 +/- 4.9 pmol/l). The maximum number of binding sites (Bmax) at mid-light and mid-dark were 1.52 +/- 0.16 and 1.35 +/- 0.08 fmol/mg protein, respectively, with no significant variation (P greater than 0.05) recorded. However, when the whole spleen was taken into consideration, the Bmax per spleen protein of the mid-light samples (253 +/- 36 fmol/spleen protein) was significantly greater than that (129 +/- 16 fmol/spleen protein) of the mid-dark samples (P less than 0.05). This indicated that in our study a diurnal rhythm of the total number of 2-[125I]iodomelatonin binding sites might exist in the chicken spleen.
Pang
C S
CS
Clarke Institute of Psychiatry, Toronto, Ontario, Canada.
Pang
S F
SF
D000818:Animals; D002645:Chickens; D002940:Circadian Rhythm; D007457:Iodine Radioisotopes; D007700:Kinetics; D008550:Melatonin / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D011897:Random Allocation; D044094:Receptors, Melatonin; D017981:Receptors, Neurotransmitter / Q000378:metabolism; D013154:Spleen / Q000187:drug effects / Q000378:metabolism*
D007457:Iodine Radioisotopes; D044094:Receptors, Melatonin; D017981:Receptors, Neurotransmitter; C024100:6-chloromelatonin; C044556:2-iodomelatonin; D008550:Melatonin