Characteristics of 3H-substance P binding sites in rat brain membranes

Original article In vitro pharmacological evaluation of the radiolabeled C-terminal substance P analogue Lys-Phe-Phe-Gly-Leu-Met-NH2: Does a specific binding site exist?

“…The majority of neurokinin recep tor specific ligands displaced the radioligand with micromolar inhibitory constants (K i -µM) reflecting the low affinity of the radioligand for these recep tors. This contrasts markedly with literature data reported for SP [17,20]. The highest affinity was found for the nonpeptidic NK1 receptor antagonist Increasing concentrations of radioligand (0.1 10 nM) were incubated with rat brain mem brane as described in the Material and methods section.…”

“…Our results further confirmed the fact that subtle differences in structure and chain length can result in striking changes in the mode of ligand binding, and presumably have an effect on GPCR signaling. The first intriguing finding came from kinetic experiments, which revealed unusually high receptor density (B max ) and a relatively high value for K d compared with those reported for SP in rat brain [20]. Park et al (1984) reported a single high affinity (K d = 0.3 nM) and low density (B max = 27.7 fmol mg protein -1 ) class of binding sites for SP in rat brain.…”

“…Fitting the direct saturation plot to a "onesite" binding model gave a K d of 7.1 ± 2.2 nM, which was in good agreement with that determined from the kinetic curves (Table II). Receptor density (B max ) was calcu lated to be 257 ± 46 fmol × mg protein -1 , a value that is several orders of magnitude greater than those reported in the literature for substance P (SP) [20]. The sites on the receptor where the radioligand binds were characterized through displacement binding experiments using receptor selective com petitors of the radioligand in rat brain membrane homogenates (Fig.…”

“…Numerous structureactivity relationship stud ies have shown that the Cterminal component of neurokinin ligands (especially the Cterminal penta peptide PheXGlyLeuMetNH 2 motif, where X is a hydrophobic amino acid residue) is critical for spe cific binding of highaffinity agonists to receptors in the tachykinin family [4,20,22,26,27,33].…”

Characterization of tachykinin receptors in isolated basilar arteries of guinea‐pig

“…types of tachykinin receptors exist: a 'SP-P' receptor in most tissues examined (Lee et al, 1983;Buck et al, 1984b;Park et al, 1984). A binding site corresponding to a 'SP-E' profile has been discovered in rat cerebral cortex (Beajouan et al, 1984;Cascieri et al, 1985), while the third type is seen in gastrointestinal and urinary bladder smooth muscle membranes (Buck et al, 1984a,b (Arunlakshana & Schild, 1959).…”