Agonist/antagonist interactions with cloned human 5-HT1A receptors: variations in intrinsic activity studied in transfected HeLa cells.
The characteristics of 5-HT1A-recognition sites and receptor-mediated release of intracellular calcium were established in two transfected HeLa cell lines (HA 6 and HA 7) expressing different levels of human 5-HT1A receptors (about 3000 and 500 fmol/mg protein, Fargin et al. 1989; 1991; Raymond et al. 1989). The pharmacological profiles of the binding (determined with [3H]8-OH-DPAT) and the calcium response (measured using Fura-2) were clearly of the 5-HT1A type. Compounds such as 5-HT, 5-CT and 8-OH-DPAT acted as full agonists on the calcium response in both HeLa cell lines. In addition, methiothepin, pindolol, NAN 190 and SDZ 216-525 (Seiler et al. 1991) acted as silent and potent antagonists. Marked differences were observed in the responses mediated in the two cell lines. EC50 values of agonists (particularly 5-HT, 5-CT, flesinoxan and 8-OH-DPAT) were higher in HA 7 cells (up to 80-fold) than in other 5-HT1A receptor models (e.g. inhibition of adenylate cyclase in calf hippocampus). Further, a variety of compounds (ipsapirone, buspirone, spiroxatrine, MDL 73005) acted as agonists in HA 6 cells, whereas they behaved as silent antagonists in HA 7 cells (which express fewer receptors). By contrast, KB values for antagonists were comparable in HA 6 and HA 7 cells. The present data show that EC50 values and intrinsic activity for a given drug are subject to large variations depending on the number of receptors expressed in the target tissue.(ABSTRACT TRUNCATED AT 250 WORDS)
Boddeke
H W
HW
Preclinical Research, SANDOZ Pharma Ltd, Basel, Switzerland.
Fargin
A
A
Raymond
J R
JR
Schoeffter
P
P
Hoyer
D
D
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003001:Cloning, Molecular; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D016257:Fura-2; D014644:Genetic Variation / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008297:Male; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000502:physiology; D012702:Serotonin Antagonists; D013552:Swine; D013764:Tetrahydronaphthalenes / Q000378:metabolism / Q000494:pharmacology; D014162:Transfection; D014316:Tritium; D010738:Type C Phospholipases / Q000378:metabolism
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D013764:Tetrahydronaphthalenes; D014316:Tritium; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D010738:Type C Phospholipases; D002118:Calcium; D016257:Fura-2