Characterization of NK-3 binding sites in rat and guinea pig cortical membranes by the selective ligand [3H]Senktide.

We have used [3H]Senktide, a selective Neurokinin B receptor ligand, for the characterization of NK-3 receptors in rat and guinea pig CNS membranes. Scatchard analysis of saturation binding studies in cerebral cortex membranes indicated that this ligand bound to a single site with apparent high affinity (KD = 4.6 +/- 1.6 and 3.1 +/- 0.37 nM, Bmax = 13.7 +/- 1.6 and 21.8 +/- 2.2 fmol/mg protein in rat and guinea pig membranes, respectively). However, in competition studies with a group of neurokinins and related peptides two different rank orders of affinities were obtained, as follows: NKB greater than [MePhe7]-NKB greater than or equal to Arg0-NKB greater than or equal to Senktide much greater than NKA greater than SP, in rat membranes, and [MePhe7]NKB greater than Senktide = NKB greater than Arg0-NKB much greater than SP greater than NKA, in guinea pig membranes.