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

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). Ligand binding studies were used to determine dissociation constants for agonist binding to the 5‐HT 1A receptor: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.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.The ability of the agonists to activate the 5‐HT 1A receptor was determined using stimulation of [ 35 S]‐GTP γ S binding. Maximal effects of agonists ( E max ) and their potencies (EC 50 ) were determined from concentration/response curves for stimulation of [ 35 S]‐GTP γ S binding.K l /K h determined from ligand binding assays correlated with the relative efficacy (relative E max ) of agonists determined in [ 35 S]‐GTP γ S 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]‐GTP γ S binding assays. 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.British Journal of Pharmacology (2003) 138 , 1129–1139. doi: 10.1038/sj.bjp.0705085