title: Desensitization of delta-opioid-induced mobilization of Ca2+ stores in NG108-15 cells.
abstract: Activation of delta-opioid receptors in NG108-15 cells induces the release of calcium from an inositol 1,4,5-trisphosphate- sensitive intracellular store. We used fura-2-based digital imaging to study the effects of prolonged exposure to agonist on opioid-induced increases in [Ca2+]i. Exposure to D-Ala2-E-Leu5 enkephalin (DADLE) (1 microM) for 30 min completely desensitized NG108-15 cells to a second DADLE-induced response. The cells recovered gradually over 25 min following washout of DADLE. The desensitization was not due to depletion of intracellular calcium stores and bradykinin failed to cross-desensitize the DADLE-evoked response, although both agonists mobilized the same Ca2+ store. Desensitization induced by 100 nM DADLE was overcome by a higher concentration of DADLE (100 microM). Treatment with 8-cpt-cAMP (0.1 mM) for 30 min did not influence the DADLE-induced increases in [CA2+]i. Phorbol dibutyrate (PdBu) (1 microM) blocked the response completely. Treatment with the inhibitor of cyclic nucleotide-dependent kinases H8 (1 microM) for 45 min did not prevent DADLE-induced desensitization. Treatment with the protein kinase C (PKC) inhibitors staurosporin (10 nM) and GF-109203X (200 nM) for 45 min reduced desensitization. However, down-regulation of PKC by 24 h exposure to PdBu (1 microM) failed to prevent the DADLE-induced desensitization in NG108-15 cells. Thus, we conclude that multiple pathways participated in desensitization of delta-receptor-mediated Ca2+ mobilization, one of which includes PKC.
authors.affiliation: Department of Pharmacology, University of Minnesota Medical School, Minneapolis 55455, USA.
authors.forename: S H
authors.initials: SH
authors.lastname: Yoon
authors.forename: W
authors.initials: W
authors.lastname: Jin
authors.forename: R J
authors.initials: RJ
authors.lastname: Spencer
authors.forename: H H
authors.initials: HH
authors.lastname: Loh
authors.forename: S A
authors.initials: SA
authors.lastname: Thayer
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D004789:Enzyme Activation / Q000502:physiology; D007527:Isoenzymes / Q000378:metabolism; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000502:physiology*; D014407:Tumor Cells, Cultured
chemical_list: D007527:Isoenzymes; D017465:Receptors, Opioid, delta; D015240:Phorbol 12,13-Dibutyrate; D016308:Enkephalin, Leucine-2-Alanine; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D002118:Calcium