Two affinities for a single antagonist at the neuronal NK1 tachykinin receptor: evidence from quantitation of receptor endocytosis.
1. In smooth muscle contractility assays, many NK1 receptor (NK1r) antagonists inhibit responses to the neurotransmitter, substance P (SP), and its analogue, septide, with markedly different potency, leading to the proposal that there is a septide-preferring receptor related to the NK1r. 2. We used fluorescence immunohistochemistry and confocal microscopy to visualize agonist-induced NK1r endocytosis and analyse agonist/antagonist interactions at native NK1r in neurons of the myenteric plexus of guinea-pig ileum. 3. SP and septide gave sigmoid log concentration-response curves and were equipotent in inducing NK1r endocytosis. 4. The NK1r antagonists, CP-99994 (2S,3S)-3-(2-methoxybenzyl)amino-2-phenylpiperidine dihydrochloride and MEN-10581, cyclo(Leu,[CH2NH]Lys(benzyloxycarbonyl)-Gln-Trp-Phe-betaAla) were both more potent in inhibiting endocytosis (50 x and 8 x greater respectively) against septide than against SP. 5. The results suggest that SP and septide interact differently with the NK1r, and that a single antagonist can exhibit different affinities at a single NK1r population, depending on the agonist with which it competes. Thus it may not be necessary to posit a separate septide-preferring tachykinin receptor.
Jenkinson
K M
KM
Department of Anatomy and Cell Biology, University of Melbourne, Parkville, Victoria, Australia. k.jenkinson@anatomy.unimelb.edu.au
Southwell
B R
BR
Furness
J B
JB
D000818:Animals; D001667:Binding, Competitive; D004305:Dose-Response Relationship, Drug; D004705:Endocytosis / Q000187:drug effects; D005260:Female; D005453:Fluorescence; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D018613:Microscopy, Confocal; D064729:Neurokinin-1 Receptor Antagonists; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D018040:Receptors, Neurokinin-1 / Q000378:metabolism*; D018042:Receptors, Neurokinin-3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D013373:Substance P / Q000031:analogs & derivatives / Q000494:pharmacology
C118600:MEN 10581; D064729:Neurokinin-1 Receptor Antagonists; D010456:Peptides, Cyclic; D010880:Piperidines; D018040:Receptors, Neurokinin-1; D018042:Receptors, Neurokinin-3; C080755:3-(2-methoxybenzylamino)-2-phenylpiperidine; D013373:Substance P; C091554:SR 142801