Comparative antagonist pharmacology at the native mouse bradykinin B2receptor: radioligand binding and smooth muscle contractility studies

Background and purpose: The aim was to characterize the recently discovered non-peptide antagonist MEN16132 at the mouse B2 receptor, relative to other antagonists. Experimental approach: [3H]-BK binding experiments used mouse lung and ileum tissue membranes and antagonist potency was measured in the isolated ileum contractility assay. Key results: Two BK binding sites resulted from saturation and homologous competition experiments. A role for the B1 receptor was excluded because of the poor affinity of B1 receptor ligands (pIC50 LF16-0687 (lung 8.9; ileum 8.8) > FR173657 (lung 8.6; ileum 8.2). BK homologous curves performed with lung membranes after treatment with the antagonist MEN16132 or Icatibant (10 nM) displayed only the low affinity site. The functional antagonism by MEN16132 (pA2 9.4) and Icatibant (pA2 9.1), towards BK (control EC50 6.1 nM) induced ileum contractions, was concentration-dependent and surmountable, but the Schild plot slope was less than unity. Conclusions and Implications: In mouse tissue, radiolabelled BK recognizes two binding sites and B2 receptor antagonists can compete only for the higher affinity one. The pharmacological profile of the novel non-peptide antagonist MEN16132 indicates that it exhibits subnanomolar affinity and potency for the mouse B2 receptor and is suitable for further characterization in in vivo pathophysiological models. British Journal of Pharmacology (2007) 150, 313–320. doi:10.1038/sj.bjp.0706995