TABLE 1

Ligand binding affinity values measured at wild-type and mutant human tachykinin NK₂ receptors

Experiments were carried out on membrane preparations from pooled clones of CHO cells stably expressing the wild-type or mutant human tachykinin NK₂ receptors by using the peptide agonist [¹²⁵I]NKA, the cyclic peptide antagonist [³H]nepadutant, and the nonpeptide antagonist [³H]saredutant as radioligands, as described under Materials and Methods. Radioligand K_d constant affinity values were calculated by means of homologous inhibition experiments and expressed in nanomolar concentration for each receptor. K_i values of the competing ligand ibodutant (in nanomolar concentration) were calculated from heterologous inhibition experiments according to the concentration and K_d of the used radioligand for each mutant receptor (see Materials and Methods). F_mut is calculated as K_i(mutant receptor)/K_i(wild-type human tachykinin NK₂ receptor) and refers to -fold decrease in the affinity of ibodutant. Significant decreases in affinity are indicated by F_mut indexes in bold. K_d and K_i values are expressed as mean and 95% confidence limits in parentheses of three experiments, each one performed in duplicate.