Delta-opioid-induced liberation of Gbetagamma mobilizes Ca2+ stores in NG108-15 cells.
Activation of delta-opioid receptors in NG108-15 cells releases Ca2+ from an intracellular store through activation of a pertussis toxin-sensitive G protein. We tested the hypothesis that activation of delta-opioid receptors mobilizes inositol 1,4,5-trisphosphate (IP(3))-sensitive Ca2+ stores via liberation of Gbetagamma. Fura-2-based digital imaging was used to study the mechanism of opioid-induced increases in [Ca2+](i) in NG108-15 cells. Exposure to D-Ala(2)-D-Leu(5) enkephalin (100 nM) for 90 s induced increases in [Ca2+](i) that were blocked by microinjection of the IP(3) receptor antagonist heparin (pipette concentration = 100 mg/ml) but not by sham injection. Microinjection of a peptide that binds Gbetagamma (QEHA, 1 mM) decreased the D-Ala(2)-D-Leu(5) enkephalin-evoked response. Microinjection of an inactive peptide (SKEE, 1 mM) that does not bind to Gbetagamma failed to inhibit the opioid-induced increase in [Ca2+](i). Microinjection of a peptide (QLKK, 15 mM) that binds to free Galpha(q) blocked the increase evoked by 3 nM bradykinin, but microinjection of an inactive peptide (ADRK, 15 mM) did not. Microinjection of QLKK did not significantly affect the opioid-induced increase in [Ca2+](i). Collectively, these data demonstrate that activation of delta-opioid receptors induces the release of Ca2+ from IP(3)-sensitive stores in NG108-15 cells through activation of the betagamma subunits of inhibitory G proteins.
Yoon
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Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.
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Loh
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Thayer
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D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry / Q000378:metabolism; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D010455:Peptides; D018160:Receptors, Cytoplasmic and Nuclear; D017465:Receptors, Opioid, delta; D016308:Enkephalin, Leucine-2-Alanine; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D001920:Bradykinin; D002118:Calcium