title: Heterologous desensitization of opioid-stimulated Ca2+ increase by bradykinin or ATP in NG108-15 cells.
abstract: Leucine-enkephalin (Leu-EK) dose-dependently elicited an increase in cytosolic Ca2+ concentration ([Ca2+]i) with an EC50 of 1.2 microM via the phosphoinositide cascade in NG108-15 cells. Chronic treatment of cells with [D-Ala2,D-Leu5]enkephalin caused time-dependent homologous desensitization. In the presence of extracellular Ca2+, ATP as well as bradykinin stimulated significantly higher increases in inositol 1,4,5-trisphosphate (IP3) generation than did Leu-EK; however, the magnitude of intracellular Ca2+ pools increased after ATP stimulation, whereas bradykinin depleted intracellular pools. Hence, cells lost their [Ca2+]i response to Leu-EK if bradykinin was first added to induce a [Ca2+]i increase, whereas the response was unchanged if Leu-EK was added after addition of ATP. When Leu-EK was added simultaneously with bradykinin or ATP, an additive response was observed in IP3 generation; however, the rise in [Ca2+]i reached the same level as that induced by bradykinin or ATP alone. In the absence of extracellular Ca2+ in which the replenishment of intracellular pools was not possible, ATP displayed an inhibitory effect similar to that of bradykinin on the Leu-EK-induced [Ca2+]i increase. Prior treatment of cells with Leu-EK slightly heterologously desensitized the action of bradykinin, but had no effect on the ATP response. Our results suggest that a shared intracellular Ca2+ pool is sensitive to the opioid, bradykinin and P2-purinoceptor agonists; however, a defined pool of phosphatidylinositol 4,5-bisphosphate or a specific phospholipase C is responsible for each receptor.
authors.affiliation: Department of Biochemistry, National Defense Medical Center, Taipei, Taiwan, Republic of China.
authors.forename: S H
authors.initials: SH
authors.lastname: Chueh
authors.forename: S L
authors.initials: SL
authors.lastname: Song
authors.forename: T Y
authors.initials: TY
authors.lastname: Liu
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000096:biosynthesis; D004743:Enkephalin, Leucine / Q000494:pharmacology*; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D005910:Glioma / Q000378:metabolism / Q000473:pathology; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology; D017465:Receptors, Opioid, delta / Q000187:drug effects; D014407:Tumor Cells, Cultured
chemical_list: D017465:Receptors, Opioid, delta; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D001920:Bradykinin; D002118:Calcium