title: Characterization of a naloxone-insensitive beta-endorphin receptor on murine peritoneal macrophages.
abstract: Previous studies from our laboratory have characterized a naloxone-insensitive beta-endorphin (beta-End) receptor on the human pro-monocytic cell line U937. Since monocytes are macrophage precursors, we sought to identify and characterize this site on fully differentiated effector macrophages. Mice (ICR females, 6-8 wk old) were injected (i.p.) with 1 mL of thioglycollate to induce an inflammatory response. Elicited cells were harvested 3 d later by lavage. Macrophages were enriched by adherence and analyzed via radioreceptor assay (with [125I] beta-End, 2,000 Ci mmol-1) as either intact cells or membrane preparations. Scatchard analysis revealed a single saturable binding site for beta-End (Kd = 9.75 +/- 2.6 x 10(-9) M; 8218 +/- 2360 sites/cell). Competition studies showed that other opiate receptor ligands including naloxone, DAMGO, U69593, or 2,5 DPDP-enkephalin were ineffective at displacing [125I] beta-End when compared to unlabeled beta-End. Analysis of competition studies utilizing fragments and analogs of beta-End revealed that beta-End (6-31) and beta-End (1-5, 16-31) were equipotent, and N-acetylated beta-End was less potent, than beta-end (1-31) in displacing [125I] beta-End binding. In contrast, beta-End (1-27) and beta-End (28-31) were ineffective. In summary, we have identified a naloxone-resistant beta-End binding site on murine peritoneal macrophages that is similar to one we have previously characterized on U937 cells and cultured murine splenocytes.
authors.affiliation: Endocrine-Neuroscience Research Laboratory, Minneapolis Medical Research Foundation, MN 55404, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Woods
authors.forename: N A
authors.initials: NA
authors.lastname: Shahabi
authors.forename: B M
authors.initials: BM
authors.lastname: Sharp
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D017737:Macrophages, Peritoneal / Q000378:metabolism*; D051379:Mice; D008813:Mice, Inbred ICR; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D010446:Peptide Fragments / Q000378:metabolism; D011869:Radioligand Assay; D011957:Receptors, Opioid / Q000187:drug effects* / Q000378:metabolism*; D001615:beta-Endorphin / Q000378:metabolism
chemical_list: D009292:Narcotic Antagonists; D010446:Peptide Fragments; D011957:Receptors, Opioid; D009270:Naloxone; D001615:beta-Endorphin