Involvement of a pertussis toxin-sensitive G protein-coupled phospholipase A2 in agonist-stimulated arachidonic acid release in membranes isolated from bovine iris sphincter smooth muscle.
We have shown that in bovine iris sphincter membranes G proteins are involved in coupling muscarinic-, PGF2 alpha-, endothelin- and platelet-activating factor receptors to the activation of phospholipase A2 and the release of arachidonic acid. GTP gamma S and GTP gamma S plus carbachol stimulated arachidonic acid release in the membranes in a dose- and time-dependent manner. Nucleotide stimulation was specific to GTP gamma S, since GDP, GDP beta S and ATP had no effect. The stimulatory effect of GTP gamma S plus carbachol was blocked by atropine and it required the presence of physiological concentrations of Ca2-. AIF4-, which bypasses the receptor and directly activates the G protein, induced arachidonic acid liberation in the intact iris sphincter, but was ineffective in the membranes. Addition of GTP gamma S plus carbachol to sphincter muscle membranes prelabeled with [3H]inositol or 3H-arachidonic acid resulted in the formation of lysophosphatidylinositol and the liberation of arachidonic acid, thus suggesting the involvement of phospholipase A2. In vitro treatment of the iris membranes with pertussis toxic inhibited arachidonic acid release by the agonists. This is in contrast to the pertussis toxin-insensitive G protein that activates phospholipase C in this tissue (22). These data demonstrate that in the iris sphincter a G protein is involved in the step between receptor activation and the activation of phospholipase A2, and that arachidonic acid release in this tissue is mediated by a pertussis-toxin-sensitive G protein-coupled phospholipase A2. Thus, GTP can regulate arachidonic acid release and its subsequent conversion into eicosanoids by stimulating its formation.
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912-2100.
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Yousufzai
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Abdel-Latif
D000535:Aluminum / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D005461:Fluorine / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D007498:Iris / Q000378:metabolism*; D008246:Lysophospholipids / Q000378:metabolism; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009711:Nucleotides / Q000494:pharmacology; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D013347:Subcellular Fractions / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D008246:Lysophospholipids; D009711:Nucleotides; D010716:Phosphatidylinositols; D010566:Virulence Factors, Bordetella; C025449:lysophosphatidylinositol; C053629:fluoroaluminum; D016718:Arachidonic Acid; D005461:Fluorine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002217:Carbachol; D000535:Aluminum; D037342:Pertussis Toxin; D010741:Phospholipases A; D054467:Phospholipases A2; D019204:GTP-Binding Proteins; D002118:Calcium