Functional and radioligand binding characterization of rat 5-HT6 receptors stably expressed in HEK293 cells.
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.
Boess
F G
FG
Pharma Division, F. Hoffmann-La Roche Ltd., Basel, Switzerland.
Monsma
F J
FJ
Carolo
C
C
Meyer
V
V
Rudler
A
A
Zwingelstein
C
C
Sleight
A J
AJ
D000262:Adenylyl Cyclases / Q000096:biosynthesis; D000818:Animals; D002460:Cell Line; D018076:DNA, Complementary / Q000096:biosynthesis; D007700:Kinetics; D008238:Lysergic Acid Diethylamide / Q000378:metabolism / Q000494:pharmacology; D008566:Membranes / Q000378:metabolism; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis; D011869:Radioligand Assay; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D012702:Serotonin Antagonists / Q000378:metabolism / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000378:metabolism / Q000494:pharmacology; D014162:Transfection; D014363:Tryptamines / Q000378:metabolism / Q000494:pharmacology
D018076:DNA, Complementary; D012333:RNA, Messenger; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D014363:Tryptamines; D008238:Lysergic Acid Diethylamide; D000262:Adenylyl Cyclases