title: Effect of chronic D-Ala,2 D-Leu5-enkephalin or pertussis toxin treatment on the high-affinity state of delta opioid receptor in neuroblastoma x glioma NG108-15 hybrid cells.
abstract: Chronic treatment of neuroblastoma x glioma NG108-15 hybrid cells with the opioid agonist D-Ala,2 D-Leu5-enkephalin (DADLE) induces a homologous desensitization of the delta opioid receptors present in these cells. Since the Kd value of the delta opioid receptor's high-affinity state reflects the potency of the agonist, we examined the effect of receptor desensitization in NG108-15 cells on the percentage of receptor in the high-affinity state. When NG108-15 hybrid cells were treated with 10 or 100 nM DADLE for 4 hr at 24 degrees C, loss of DADLE's ability to inhibit adenylate cyclase was observed. However, when competition binding experiments were carried out with P2P3 membranes isolated from the delta opioid-desensitized hybrid cells, it was determined that 41.7 +/- 3.4% of the total binding sites remained in the high-affinity state, with no apparent alteration in the Kd value of either high- or low-affinity states. Similarly, when NG108-15 cells were treated with 100 ng/ml of pertussis toxin for 3 hr at 37 degrees C, 39.9 +/- 3.6% of the binding sites remained in the high-affinity state. This reduction in the percentage of receptor in high-affinity state was agonist specific, for chronic treatment of hybrid cells with levorphanol, a partial agonist, or the antagonist naloxone did not alter the percentage of opioid receptors in the high-affinity state. Furthermore, the delta opioid receptors remaining in the high-affinity state after chronic DADLE treatment were still sensitive to both Na+ and guanyldylimidodiphosphate, indicating that opioid ligand binding remained coupled to the G-proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology, University of Minnesota, Minneapolis.
authors.forename: P Y
authors.initials: PY
authors.lastname: Law
authors.forename: D S
authors.initials: DS
authors.lastname: Hom
authors.forename: H H
authors.initials: HH
authors.lastname: Loh
mesh_terms: D037361:Adenylate Cyclase Toxin; D001667:Binding, Competitive; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000502:physiology; D005910:Glioma / Q000378:metabolism / Q000473:pathology; D006153:Guanosine Diphosphate / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006801:Humans; D006822:Hybrid Cells / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology; D037342:Pertussis Toxin; D011957:Receptors, Opioid / Q000187:drug effects*; D017465:Receptors, Opioid, delta; D012964:Sodium / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
chemical_list: D037361:Adenylate Cyclase Toxin; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; D006165:Guanylyl Imidodiphosphate; D016308:Enkephalin, Leucine-2-Alanine; D012964:Sodium; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D008274:Magnesium