Differentiation between partial and silent 5-HT1D beta receptor antagonists using rat C6-glial and Chinese hamster ovary cell lines permanently transfected with a cloned human 5-HT1D beta receptor gene.
Intrinsic activities of serotonin (5-HT) receptor ligands at cloned human 5-HT1D beta receptor sites were determined by measuring cAMP responses in two permanently transfected cell types: rat C6-glial and Chinese hamster ovary (CHO)-K1 cells. Both transfected cell lines expressed a similar 5-HT1D beta receptor density (361 to 448 fmol/mg protein) and displayed a number of similar cAMP responses: marked inhibition of forskolin-stimulated cAMP formation by 5-HT; a similar agonist potency and efficacy with 5-carboxamidotryptamine (5-CT), 5-methoxytryptamine, bufotenine, sumatriptan, 7-trifluoromethyl-4(4-methyl-1-piperazinyl)-pyrolo-(1,2-a)quinoxal ine (CGS 12066B), 5-methoxy-3(1,2,3,6-tetrahydro-4-pyridinyl)1H-indole (RU 24,969), and tryptamine, their maximal effect being comparable to that of 5-HT; less agonist efficacy with m-trifluoro-phenyl-piperazine (TFMPP) (it inhibited at most 63% of stimulated cAMP formation); and antagonist activity against the 5-CT-mediated agonist response with methiothepin, 2'-methyl-4-(5-methyl-[1,2,4]oxadiazol-3-yl)-biphenyl-4-carboxylic acid [4-methoxy-3-(4-methyl-piperazin-1-yl)-phenyl]-amide (GR 127,935), and ritanserin. Metergoline and 1-naphtylpiperazine showed different intrinsic activities. In contrast to their pronounced antagonist activity in the transfected CHO-K1 cell line, the antagonist effect was only partial and absent for metergoline and 1-naphtylpiperazine in the transfected C6-glial cell line, respectively. In conclusion, these cell lines are useful as a tool to measure with high sensitivity differences in intrinsic activities of 5-HT receptor ligands and, therefore, discriminate between silent antagonists (no intrinsic activity) and antagonists with intrinsic activity (i.e. partial agonists), even though this intrinsic activity may be relatively weak.
Pauwels
P J
PJ
Laboratory of Cellular and Molecular Neurobiology, Centre de Recherche Pierre Fabre, Castres, France.
Colpaert
F C
FC
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D003001:Cloning, Molecular; D006224:Cricetinae; D000242:Cyclic AMP / Q000096:biosynthesis; D006801:Humans; D007700:Kinetics; D008024:Ligands; D009457:Neuroglia / Q000166:cytology; D011869:Radioligand Assay; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013268:Stimulation, Chemical; D014162:Transfection
D008024:Ligands; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; C047087:5-carboxamidotryptamine; D000242:Cyclic AMP