The 5-hydroxytryptamine6 receptor-selective radioligand [3H]Ro 63-0563 labels 5-hydroxytryptamine receptor binding sites in rat and porcine striatum.
Ro 63-0563 [4-amino-N-(2,6 bis-methylamino-pyridin-4-yl)-benzene sulfonamide] is a high affinity 5-hydroxytryptamine6 (HT6) receptor antagonist with more than 100-fold selectivity for the 5-HT6 receptor compared with 69 other receptors and binding sites. The present study describes the properties of [3H]Ro 63-0563, the first selective 5-HT6 receptor radioligand. Specific binding of [3H]Ro 63-0563 (nonspecific binding defined in the presence of 10 microM methiothepin) to recombinant rat and human 5-HT6 receptors was saturable, rapid, and reversible with equilibrium dissociation constants (Kd) of 6.8 nM and 4.96 nM, respectively. The pharmacological profile of the rat 5-HT6 receptor labeled with [3H]Ro 63-0563 (methiothepin > D-lysergic acid diethylamide > clozapine approximately Ro 63-0563 > lisuride > ergotamine approximately Ro 04-6790 > 5-HT > amitriptyline approximately metergoline approximately mianserin approximately ritanserin > methysergide > mesulergine) was similar to that obtained by using either [3H]D-lysergic acide diethylamide or [3H]5-HT as radioligand. In equilibrium binding studies with rat striatal membranes, [3H]Ro 63-0563 labeled a single binding site with Kd and Bmax values of 11. 7 nM and 175 fmol/mg protein, respectively. In porcine striatal membranes, [3H]Ro 63-0563 also labeled a single binding site with Kd and Bmax values of 8.0 nM and 130 fmol/mg protein, respectively. The affinities of 14 5-HT6 receptor ligands at this binding site were similar to those found for the recombinant rat and human 5-HT6 receptor, which suggested the presence of 5-HT6 receptors in porcine striatum.
Boess
F G
FG
Pharma Division, Preclinical Research, F. Hoffmann-La Roche, Ltd., 4070 Basel, Switzerland.
Riemer
C
C
Bös
M
M
Bentley
J
J
Bourson
A
A
Sleight
A J
AJ
D000631:Aminopyridines / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D003342:Corpus Striatum / Q000378:metabolism / Q000648:ultrastructure*; D006367:HeLa Cells; D006801:Humans; D011869:Radioligand Assay; D051381:Rats; D011985:Receptors, Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000378:metabolism* / Q000494:pharmacology; D013045:Species Specificity; D013552:Swine; D014316:Tritium; D000096926:Benzenesulfonamides
D000631:Aminopyridines; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D014316:Tritium; C114164:4-amino-N-(2,6 bis-methylamino-pyridin-4-yl)-benzene sulfonamide; D000096926:Benzenesulfonamides; C097216:serotonin 6 receptor