Analysis of molecular determinants of affinity and relative efficacy of a series of R- and S-2-(dipropylamino)tetralins at the 5-HT 1A serotonin receptor

Abstract

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 [ 3H]-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 [ 3H]-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 1 sites were determined. 3. The ability of the agonists to activate the 5-HT 1A receptor was determined using stimulation of [ 35S]-GTPγS binding, Maximal effects of agonists (E max) and their potencies (EC 50) were determined from concentration/response curves for stimulation of [ 35S]-GTPγS binding. 4. K 1/K h determined from ligand binding assays correlated with the relative efficacy (relative E max) of agonists determined in [ 35S]-GTPγS binding assays. There was also a correlation between K 1/K h and K 1/EC 50 for agonists determined from ligand binding and [ 35S]-GTPγS 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 1/K h for predicting the relative efficacy of agonists.