Functional and radioligand binding characterization of rat 5-HT6 receptors stably expressed in HEK293 cells

• Published in: Neuropharmacology Vol. 36; no. 4-5; pp. 713 - 720
• Main Authors: Boess, F G, Monsma, Jr, F J, Carolo, C, Meyer, V, Rudler, A, Zwingelstein, C, Sleight, A J
• Format: Journal Article
• Language: English
• Published: England 01-04-1997
• Subjects: Adenylyl Cyclases - biosynthesis; Animals; Cell Line; DNA, Complementary - biosynthesis; Kinetics; Lysergic Acid Diethylamide - metabolism; Lysergic Acid Diethylamide - pharmacology; Membranes - metabolism; Molecular Sequence Data; Radioligand Assay; Rats; Receptors, Serotonin - drug effects; Receptors, Serotonin - genetics; Receptors, Serotonin - metabolism; RNA, Messenger - biosynthesis; Serotonin Antagonists - metabolism; Serotonin Antagonists - pharmacology; Serotonin Receptor Agonists - metabolism; Serotonin Receptor Agonists - pharmacology; Transfection; Tryptamines - metabolism; Tryptamines - pharmacology
• ISSN: 0028-3908
• DOI: 10.1016/S0028-3908(97)00019-1

We have stably expressed the rat 5-HT6 receptor in HEK293 cells at a density of > 2 pmol/mg protein, as determined in equilibrium binding studies with [3H]-LSD and [3H]-5-HT and compared the affinity of a range of compounds in competition binding experiments with either [3H]-LSD or [3H]-5-HT as radioligand. A variety of tryptamine derivatives were tested and showed a significantly higher affinity when the 5-HT6 receptor was labelled with [3H]-5-HT, whereas ergoline compounds and several antagonists had higher affinities when [3H]-LSD was used as radioligand. Subsequently we examined the ability of LSD, 5-HT and a number of tryptamine derivatives to stimulate cAMP accumulation in order to determine their agonist potency and efficacy. We observed the following rank order of potency: LSD > omega-N-methyl-5-HT approximately bufotenine approximately 5- methoxytryptamine > 5-HT > 2-methyl-5-HT approximately 5-benzyloxytryptamine approximately tryptamine > 5-carboxamidotryptamine > > 5-HTQ. LSD, lisuride, 2-methyl-5-HT, tryptamine and 5-benzyloxytryptamine behaved as partial agonists relative to 5-HT. The rank order of potency of the tryptamine compounds correlated well with their affinities determined in binding assays. In addition, we have tested a number of antagonists in this system (rank order of potency: methiothepin, clozapine, mianserin and ritanserin). This characterization of the pharmacological properties of recombinant 5-HT6 receptor will facilitate the identification of 5-HT6 receptor-mediated responses in physiological systems.