Characterization of NK-1 receptors in guinea pig and rat brain membranes with NK-1 peptides and a non-peptide antagonist

Abstract

The major finding of the present investigation is the demonstration of different NK-1 receptors in rat and guinea pig brain membranes with CP 96345 (non-peptide NK-1 antagonist) and R-544 (NK-1 peptide antagonist). We used [ 3H]Sar 9, Me(O 2) 11]SP, the highly selective ligand for NK-1 receptor to compare NK-1 binding sites in rat and guinea pig brain membranes. Scarchard analysis revealed the existence of a single population of [ 3H][Sar 9, Met(O 2) 11]SP binding sites in both preparations. The affinity and the maximal number of bindind sites were found closely similar in rat ( K d 2 nM, B max = 37 fmol/mg protein) and guinea pig brain membranes ( K d = 3 nM, B max = 25 fmol/mg of protein). The order of potency of neurokinins to inhibit [ 3H][Sar 9, Met(O 2) 11]SP binding from rat brain (SP > NKA > NKB) was found different of that observed on guinea pig brain (SP > NKB > NKA). Results obtained with [Sar 9, Met(O 2) 11]SP, [βAla 8]NKA(4–10) and [MePhe 7]NKB suggest that selective agonists cannot discriminate between NK-1 receptors of different species. Using the non-peptide antagonist CP 96345 and the tripeptide R-544, we found that these two NK-1 antagonists discriminate between rat and guinea pig [ 3H][Sar 9, Met(O 2) 11]SP binding sites.