title: Characterization and autoradiographic localization of neurotensin binding sites in human sigmoid colon.
abstract: Radioiodinated neurotensin ((125)I-NT) was used to characterize and localize NT binding sites in normal human sigmoid colon. Specimens were obtained from patients (30-77 years old) undergoing resection for colon carcinoma. Specific binding of (125)I-NT to sigmoid circular muscle membranes was enhanced by o-phenanthroline (1 mM) but other peptidase inhibitors were ineffective. (125)I-NT bound to a high-affinity site of K(d) = 0.88 +/- 0.09 nM and B(max) = 4.03 +/- 0.66 fmol/mg of wet weight tissue (n = 14), although in the majority of patients another site, of low but variable affinity, could also be detected. Specific binding of 50 pM (125)I-NT was inhibited by NT(8-13) > NT > SR142948A > or = neuromedin N > or = SR48692, consistent with binding to the NT1 receptor. In autoradiographic studies, dense specific binding of (125)I-NT was seen over myenteric and submucosal ganglia, moderate binding over circular muscle, and sparse binding over longitudinal muscle and taenia coli. Levocabastine, which has affinity for the NT2 receptor, did not inhibit specific binding of (125)I-NT in membrane competition or autoradiographic studies. NT contracted sigmoid colon circular muscle strips with a pD(2) value of 6.8 +/- 0.2 nM (n = 25). The contractile responses to NT were significantly potentiated in the presence of tetrodotoxin (1 microM), indicating a neural component. Results from functional studies support actions for NT on both muscle and enteric neurons, consistent with the presence of NT receptors on circular muscle and ganglia of human sigmoid colon. The lack of inhibition by levocabastine suggests that the second binding site detected does not correspond to the NT2 receptor.
authors.affiliation: School of Physiology and Pharmacology, University of New South Wales, Australia.
authors.forename: Y
authors.initials: Y
authors.lastname: Azriel
authors.forename: E
authors.initials: E
authors.lastname: Burcher
mesh_terms: D000328:Adult; D000368:Aged; D001345:Autoradiography; D001667:Binding, Competitive / Q000187:drug effects; D012809:Colon, Sigmoid / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D017615:Enteric Nervous System / Q000378:metabolism; D005260:Female; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation / Q000378:metabolism; D009496:Neurotensin / Q000378:metabolism* / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology; D010618:Phenanthrolines / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D018028:Receptors, Neurotensin / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D006634:Histamine H1 Antagonists; D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D010618:Phenanthrolines; D010880:Piperidines; D011480:Protease Inhibitors; D018028:Receptors, Neurotensin; C114036:neurotensin type 1 receptor; C042090:neuromedin N; D009496:Neurotensin; D013779:Tetrodotoxin; C047340:levocabastine; C025205:1,10-phenanthroline