HPLC-purified 2-[125I]iodomelatonin labels multiple binding sites in hamster brain.
Binding of 2-[125I]iodomelatonin in hamster brain synaptosomal membranes at 0 degrees C is rapid, saturable, reversible and sensitive to heat and trypsin treatment. Computer resolution of curvilinear Scatchard plots yielded high- and low-affinity components as follows: Kd1 = 0.32 +/- 0.14 nM, Bmax1 = 5.6 +/- 1.7 fmol/mg protein and Kd2 = 10.5 +/- 3.2 nM, Bmax2 = 123 +/- 33 fmol/mg protein (n = 3). Competition experiments indicated that 2-iodomelatonin and prazosin are the most potent inhibitors of high-affinity binding. Unlike prazosin, several alpha-adrenergic agents and various neurotransmitters were ineffective. These findings suggest that prazosin may be a potent antagonist at a unique, non-alpha-adrenergic, high-affinity binding site for melatonin.
Niles
L P
LP
Department of Neurosciences, McMaster University, Hamilton, Ontario, Canada.
Pickering
D S
DS
Sayer
B G
BG
D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D006224:Cricetinae; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008550:Melatonin / Q000302:isolation & purification / Q000378:metabolism*; D011224:Prazosin / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013574:Synaptosomes / Q000378:metabolism
D007457:Iodine Radioisotopes; D008550:Melatonin; D011224:Prazosin