[3H]-5-carboxamidotryptamine labels 5-HT1D binding sites in bovine substantia nigra.
1. [3H]-5-hydroxytryptamine (5-HT) has been shown to radiolabel at least five types of 5-HT binding sites in mammalian brain tissue, 5-HT1A, 5-HT1C, 5-HT1D and 5-HT1D and 5-HT1E (Frazer et al., 1990). Selective masking of 5-HT1A and 5-HT1C receptors, has uncovered binding sites which display both high (5-HT1D) and low (5-HT1E) affinity for 5-carboxamidotryptamine (5-CT). By utilizing [3H]-5-CT we have eliminated a portion of the complex binding (5-HT1E) seen when [3H]-5-HT is used as a radioligand. 2. [3H]-5-CT binding to 5-HT1D sites in bovine substantia nigra was rapid, reversible and saturable, displaying high affinity (Kd = 0.38 +/- 0.04 nM) and low non-specific binding (> 90% specific binding). 3. In bovine substantia nigra, [3H]-5-CT labelled an equivalent number of binding sites to [3H]-5-CT (403 +/- 18 and 362 +/- 20 fmol mg-1 protein, respectively) and binding was sensitive to guanine nucleotides. 4. A linear correlation (r2 = 0.99) existed between the potency of compounds to displace [3H]-5-HT and [3H]-5-CT in bovine substantia nigra. 5. Therefore, [3H]-5-CT is a novel radioligand for the examination of 5-HT1-like binding sites, which under proper experimental conditions can be used to radiolabel selectively 5-HT-1D-like binding sites.
Nowak
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Bristol-Myers Squibb Pharmaceutical Research Institute, Neuropharmacology/Department 404, Wallingford, CT 06492.
Mahle
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Yocca
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D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002417:Cattle; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D007553:Isotope Labeling; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D011869:Radioligand Assay; D011985:Receptors, Serotonin / Q000187:drug effects*; D012044:Regression Analysis; D012701:Serotonin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000493:pharmacokinetics / Q000494:pharmacology*; D013378:Substantia Nigra / Q000187:drug effects / Q000378:metabolism*
D011985:Receptors, Serotonin; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D006165:Guanylyl Imidodiphosphate; C047087:5-carboxamidotryptamine