High-affinity [3H]6-nitroquipazine binding sites in rat brain.
6-Nitroquipazine is a very potent and selective inhibitor of neuronal 5-hydroxytryptamine (5-HT; serotonin) uptake. We have characterized the specific binding of [3H]6-nitroquipazine to rat brain membranes at 22 degrees C. The present results indicate the presence of a single saturable high-affinity binding component for [3H]6-nitroquipazine. Scatchard analysis revealed an apparent equilibrium dissociation constant (Kd) of 93.0 +/- 2.23 pM, and a maximal number of binding sites (Bmax) of 831.7 +/- 18.7 fmol/mg protein (mean +/- S.D., n = 4). The kinetically derived dissociation constant was 74.5 pM. [3H]6-Nitroquipazine binding was inhibited selectively by 5-HT uptake inhibitors, and a good correlation was demonstrated between the potency of various drugs to inhibit [3H]6-nitroquipazine binding and [3H]5-HT uptake. The highest densities of [3H]6-nitroquipazine binding were obtained in the hypothalamus and midbrain, intermediate binding was observed in the striatum, hippocampus, medulla oblongata and cortex, and the lowest binding was observed in the cerebellum. Lesioning of 5-HT neurons with p-chloroamphetamine resulted in a 72% reduction in [3H]6-nitroquipazine binding compared to controls. These results indicate that the binding site specifically labelled by [3H]6-nitroquipazine is associated with the neuronal 5-HT transporter complex. [3H]6-Nitroquipazine is an excellent radioligand for the study of the 5-HT uptake system.
Department of Radiopharmaceutical Chemistry, Faculty of Pharmacy, University of Fukuyama, Japan.
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Hashimoto
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Goromaru
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects*; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism; D011804:Quinolines; D011814:Quipazine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism; D012702:Serotonin Antagonists / Q000378:metabolism*; D010133:p-Chloroamphetamine / Q000494:pharmacology
D011804:Quinolines; D012702:Serotonin Antagonists; D012701:Serotonin; D011814:Quipazine; D006897:Hydroxyindoleacetic Acid; D010133:p-Chloroamphetamine; C031227:6-nitroquipazine