CHARACTERIZATION OF NK-3 BINDING-SITES IN RAT AND GUINEA-PIG CORTICAL MEMBRANES BY THE SELECTIVE LIGAND [H-3] SENKTIDE

We have used [H-3] 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 (K(D) = 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 > [MePhe7]-NKB greater-than-or-equal-to Arg0-NKB greater-than-or-equal-to Senktide >> NKA > SP, in rat membranes, and [MePhe7]NKB > Senktide = NKB > Arg0-NKB >> SP > NKA, in guinea pig membranes.