Pharmacological analysis of [3H]-senktide binding to NK3 tachykinin receptors in guinea-pig ileum longitudinal muscle-myenteric plexus and cerebral cortex membranes.
1. The binding properties and pharmacological specificity of the selective NK3 tachykinin receptor agonist [3H))-senktide [( 3H]-succinyl[Asp6,MePhe8] substance P (6-11] have been examined in homogenates of guinea-pig ileum longitudinal muscle-myenteric plexus (LM/MP) and cerebral cortex. 2. Scatchard analysis of saturation binding studies in guinea-pig ileum LM/MP and cerebral cortex membranes indicated that [3H]-senktide bound to a single site with apparent high affinity, KD = 2.21 +/- 0.65 nM; Bmax = 13.49 +/- 0.04 fmol mg-1 protein in ileum and KD = 8.52 +/- 0.45 nM; Bmax = 76.3 +/- 1.6 fmol mg-1 protein in cortex (values are means +/- ranges; n = 2). 3. The pharmacological profile for tachykinins and analogues in displacing [3H]-senktide from ileum membranes was: [MePhe7] neurokinin B greater than neurokinin B (NKB) congruent to senktide greater than eledoisin greater than substance P (SP) greater than neurokinin A(NKA) greater than physalaemin greater than [Sar9,Met(O2)11]SP greater than [Nle10]NKA(4-10) = [Glp6,L-Pro9]-SP(6-11) greater than substance P methyl ester, consistent with [3H]-senktide binding to an NK3 subtype of tachykinin receptor. A similar rank order of affinity was obtained for these peptides in displacing [3H]-senktide from cortex membranes. 4. Several tachykinin receptor agonists were tested for their ability to displace [3H]-senktide from ileal and cortical NK3 binding sites and were found to be either weak displacers (pIC50 less than 5.00) or inactive. 5. The binding of [3H]-senktide to cortex membranes was inhibited by GTP (p1C,0 = 6.49)and GTP-gamma- S (p1C,0 = 6.67) with ATP being at least three orders of magnitude less potent (pIC50 = 3.55). 6. These results indicate that both central and peripheral NK3 receptors share a similar pharmacological specificity and that they may be labelled selectively with the NK3 receptor agonist [3H]-senktide.
University Department of Pharmacology, Oxford.
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S
Guard
S P
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Watson
J E
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Maggio
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Too
K J
KJ
Watling
D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009197:Myenteric Plexus / Q000187:drug effects / Q000378:metabolism; D009711:Nucleotides / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism*; D011869:Radioligand Assay; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D018039:Receptors, Tachykinin; D013373:Substance P / Q000031:analogs & derivatives* / Q000378:metabolism; D015320:Tachykinins / Q000494:pharmacology
D007457:Iodine Radioisotopes; D009711:Nucleotides; D010446:Peptide Fragments; D017981:Receptors, Neurotransmitter; D018039:Receptors, Tachykinin; D015320:Tachykinins; C054724:senktide; D013373:Substance P