Comparative antagonist pharmacology at the native mouse bradykinin B2 receptor: 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 <5). MEN16132, and the other reference antagonists, inhibited only one portion of BK specific binding, and the rank order of potency was (pIC₅₀): Icatibant (lung 10.7; ileum 10.2)=MEN11270 (lung 10.4; ileum 9.9)=MEN16132 (lung 10.5; ileum 9.9). > 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; published online 18 December 2006 [ABSTRACT FROM AUTHOR]