Detection of a Novel Serotonin Receptor Subtype (5‐HT_1E) in Human Brain: Interaction with a GTP‐Binding Protein

Abstract

[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)

[3H]‐5‐carboxamidotryptamine labels 5‐HT1D binding sites in bovine substantia nigra

“…(Pedigo et al, 1981;Heuring & Peroutka, 1987 Hoyer et al, 1985;Heuring & Peroutka, 1987;Leonhardt et al, 1989), which increases the complexity of binding curves and data analysis.…”

“…The hypothesis that 5-HTIB receptors represent the species homologue of the 5-HTID receptor (Adham et al, 1992) (Leonhardt et al, 1989;Weisberg & Teitler, 1992;Beer et al, 1992 (Hamblin & Metcalf, 1991) and a 5-HTIE receptor (McAllister et al, 1992). Also as predicted on the basis of radioligand binding assays performed in brain membrane homogenates from numerous mammalian species (Leonhardt et al, 1989;Beer et al, 1992), the human 5-HTIE receptor as opposed to the 5-HTID receptor, has been shown to have a low affinity for 5-CT, ergotamine and sumatriptan. Recently, based upon sequence homology, another new member of the 5-HT, receptor family has been described (Adham et al, 1993).…”

“…While the endogenous ligand 5-HT activates numerous 5-HT receptor types, 5-HTI-like receptors alone are suggested to display an equally high affinity for the agonist, 5-carboxamidotryptamine (5-CT, Bradley et al, 1986). Pharmacological approaches have suggested that 5-HTI-like receptors are a heterogeneous group consisting of 5-HTIA, c, (El Mestikawy et al, 1991;Middlemiss & Hutson, 1990;Hoyer, 1988;Waeber et al, 1990;Leonhardt et al, 1989).…”

“…However, [3H]-5-HT in the presence of the above masking ligands has been shown to recognize a heterogeneous population of binding sites in porcine caudate (Sumner & Humphrey, 1989) and human cortex (Leonhardt et al, 1989). It has also been demonstrated that in the presence of 100nM cyanopindolol (to mask 5-HTIA and 5-HTIB sites) and 100nM mesulergine, 5-CT and sumatriptan produced biphasic displacement of [3H]-5-HT binding in the cortex and/or caudate of dog, guinea-pig, rabbit, pig, man, hamster, and calf .…”

Meta‐chlorophenylpiperazine attenuates formalin‐induced nociceptive responses through 5‐HT1/2 receptors in both normal and diabetic mice

“…On the other hand, studies using radioligand binding assays and molecular biology techniques have revealed that at least four types of 5-HT receptors exist in the vertebrate CNS, i.e., 5-HT1, 5-HT2, 5-HT3 and 5-HT4 (Peroutka & Snyder, 1979;Kilpatrick et al, 1987;Bockaert et al, 1992). The 5-HT, receptor site has been further divided into six distinct receptor subtypes: 5-HTIA, 5-HTIB, 5-HTc, 5-HTID, 5-HTlE and 5-HTIF (Pedigo et al, 1981;Pazos et al, 1985;Heuring & Peroutka, 1987;Leonhardt et al, 1989;Adham et al, 1993). The 5-HTc receptor shares homology with the 5-HT2 receptor subtype and has recently been termed the 5-HT2c receptor while the 5-HT2 receptor has been renamed the 5-HT2A receptor (Humphrey et al, 1993).…”