Analysis of molecular determinants of affinity and relative efficacy of a series of R- and S-2-(dipropylamino)tetralins at the 5-HT1A serotonin receptor.
1. Factors influencing agonist affinity and relative efficacy have been studied for the 5-HT(1A) serotonin receptor using membranes of CHO cells expressing the human form of the receptor and a series of R-and S-2-(dipropylamino)tetralins (nonhydroxylated and monohydroxylated (5-OH, 6-OH, 7-OH, 8-OH) species). 2. Ligand binding studies were used to determine dissociation constants for agonist binding to the 5-HT(1A) receptor: (a) K(i) values for agonists were determined in competition versus the binding of the agonist [(3)H]-8-OH DPAT. Competition data were all fitted best by a one-binding site model. (b) K(i) values for agonists were also determined in competition versus the binding of the antagonist [(3)H]-NAD-199. Competition data were all fitted best by a two-binding site model, and agonist affinities for the higher (K(h)) and lower affinity (K(l)) sites were determined. 3. The ability of the agonists to activate the 5-HT(1A) receptor was determined using stimulation of [(35)S]-GTPgammaS binding. Maximal effects of agonists (E(max)) and their potencies (EC(50)) were determined from concentration/response curves for stimulation of [(35)S]-GTPgammaS binding. 4. K(l)/K(h) determined from ligand binding assays correlated with the relative efficacy (relative E(max)) of agonists determined in [(35)S]-GTPgammaS binding assays. There was also a correlation between K(l)/K(h) and K(l)/EC(50) for agonists determined from ligand binding and [(35)S]-GTPgammaS binding assays. 5. Simulations of agonist binding and effect data were performed using the Ternary Complex Model in order to assess the use of K(l)/K(h) for predicting the relative efficacy of agonists.
Alder
J Tracy
JT
School of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading, Berkshire RG6 6AJ U.K.
Hacksell
Uli
U
Strange
Philip G
PG
D000818:Animals; D016466:CHO Cells / Q000187:drug effects / Q000378:metabolism*; D002417:Cattle; D006224:Cricetinae; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D008954:Models, Biological; D015335:Molecular Probes / Q000138:chemical synthesis* / Q000378:metabolism; D044282:Receptor, Serotonin, 5-HT1A / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D017366:Serotonin Receptor Agonists / Q000138:chemical synthesis* / Q000378:metabolism / Q000493:pharmacokinetics*; D013764:Tetrahydronaphthalenes / Q000138:chemical synthesis* / Q000493:pharmacokinetics*
D015335:Molecular Probes; D017366:Serotonin Receptor Agonists; D013764:Tetrahydronaphthalenes; D044282:Receptor, Serotonin, 5-HT1A; D016244:Guanosine 5'-O-(3-Thiotriphosphate)