Detection of a novel serotonin receptor subtype (5-HT1E) in human brain: interaction with a GTP-binding protein.
[3H]Serotonin (5-hydroxytryptamine, [3H]5-HT) was used as a radioligand probe of brain 5-HT receptors in homogenates of human cortical tissue. Two binding sites were detected in the presence of 1 microM pindolol (to block 5-HT1A and 5-HT1B receptors), and 100 nM mesulergine (to block 5-HT1C and 5-HT2 receptors). One of these sites demonstrated high affinity for 5-carboxyamidotryptamine (5-CT) and ergotamine, consistent with the known pharmacology of the 5-HT1D receptor; the second site demonstrated low affinity for 5-CT and ergotamine. Computer-assisted analyses indicated that both drugs displayed high affinities (Ki values of 1.1 nM and 0.3 nM for 5-CT and ergotamine, respectively) for 55% of the sites and low affinities (Ki values of 910 nM and 155 nM for 5-CT and ergotamine, respectively) for 45% of the sites. To investigate the non-5-HT1D component of the binding, 100 nM 5-CT (to block 5-HT1A, 5-HT1B, and 5-HT1D receptors) was coincubated with [3H]5-HT, membranes, and mesulergine. The remaining [3H]5-HT binding (hereafter referred to as "5-HT1E") displayed high affinity and saturability (KD, 5.3 nM; Bmax, 83 fmol/mg) in human cortical tissue. Competition studies with nonradioactive drugs indicated that, of the drugs tested, 5-CT and ergotamine displayed the highest selectivity for the 5-HT1D site versus the 5-HT1E site.(ABSTRACT TRUNCATED AT 250 WORDS)
Leonhardt
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S
Department of Pharmacology and Toxicology, Albany Medical College, New York 12208.
Herrick-Davis
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K
Titeler
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M
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D004878:Ergotamine / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000378:metabolism*; D006801:Humans; D011985:Receptors, Serotonin / Q000378:metabolism*; D012701:Serotonin / Q000031:analogs & derivatives / Q000378:metabolism; D013873:Thionucleotides / Q000378:metabolism*
D011985:Receptors, Serotonin; D013873:Thionucleotides; D012701:Serotonin; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; C047087:5-carboxamidotryptamine; D004878:Ergotamine