Enkephalin activates the phospholipase C/Ca2+ system through cross-talk between opioid receptors and P2-purinergic or bradykinin receptors in NG 108-15 cells. A permissive role for pertussis toxin-sensitive G-proteins.
In an NG 108-15 neuroblastoma x glioma hybrid cell suspension, extracellular ATP (via P2-purinergic receptors) and bradykinin stimulated Ins(1,4,5)P3 formation, which was accompanied by an increase in the cytosolic Ca2+ concentration ([Ca2+]i). Leucine enkephalin (EK) also slightly increased [Ca2+]i in the absence, but not in the presence, of apyrase, which hydrolyses extracellular ATP and ADP to AMP. When the cells were stimulated by P2-agonists or bradykinin prior to the application of EK, EK induces a remarkable rise in [Ca2+]i. This P2-agonist- or bradykinin-assisted EK action was also observed in single cells on a coverslip. A decrease in the extracellular Ca2+ concentration only slightly lowered the EK-induced rise in [Ca2+]i, but treatment of the cells with thapsigargin, an agent which depletes Ca2+ in the Ins(1,4,5)P3-sensitive pool, almost completely abolished EK action. The observed permissive stimulation by EK of Ins(1,4,5)P3 formation induced by a P2-agonist or bradykinin may be a primary event for the EK-induced [Ca2+]i rise. These actions of EK were antagonized by naloxone and completely reversed by prior treatment of the cells with pertussis toxin, whereas the toxin hardly affected the actions of P2-agonists and bradykinin themselves. Thus EK can induce phospholipase C activation and subsequent Ca2+ mobilization, provided that the cells have been previously or are simultaneously stimulated by endogenous adenine nucleotides or by externally applied P2-agonists or bradykinin. In this cross-talk mechanism between opioid receptors and these Ca(2+)-mobilizing agonist receptors, pertussis toxin-sensitive G-proteins play a permissive role.
Department of Physical Biochemistry, Institute of Endocrinology, Gunma University, Maebashi, Japan.
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F
Okajima
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H
Tomura
Y
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Kondo
D000255:Adenosine Triphosphate / Q000494:pharmacology; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004743:Enkephalin, Leucine / Q000494:pharmacology; D004745:Enkephalins / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000502:physiology*; D005910:Glioma; D006822:Hybrid Cells; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D009270:Naloxone / Q000494:pharmacology; D009447:Neuroblastoma; D037342:Pertussis Toxin; D018002:Receptors, Bradykinin; D017981:Receptors, Neurotransmitter / Q000502:physiology*; D011957:Receptors, Opioid / Q000502:physiology*; D011983:Receptors, Purinergic / Q000502:physiology*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D004745:Enkephalins; D018002:Receptors, Bradykinin; D017981:Receptors, Neurotransmitter; D011957:Receptors, Opioid; D011983:Receptors, Purinergic; D013729:Terpenes; D010566:Virulence Factors, Bordetella; D009270:Naloxone; D004743:Enkephalin, Leucine; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D001920:Bradykinin; D002118:Calcium