The G protein beta gamma subunit transduces the muscarinic receptor signal for Ca2+ release in Xenopus oocytes.
At least 30 G protein-linked receptors stimulate phosphatidylinositol 4,5-bisphosphate phosphodiesterase (phospholipase C beta, PLC beta) through G protein subunits to release intracellular calcium from the endoplasmic reticulum (Clapham, D. E. (1995) Cell 80, 259-268). Although both G alpha and G beta gamma G protein subunits have been shown to activate purified PLC beta in vitro, G alpha q has been presumed to mediate the pertussis toxin-insensitive response in vivo. In this study, we show that G beta gamma plays a dominant role in muscarinic-mediated activation of PLC beta by employing the Xenopus oocyte expression system. Antisense nucleotides and antibodies to G alpha q/11 blocked the m3-mediated signal transduction by inhibiting interaction of the muscarinic receptor with the G protein. Agents that specifically bound free G beta gamma subunits (G alpha-GDP and a beta-adrenergic receptor kinase fragment) inhibited acetylcholine-induced signal transduction to PLC beta, and injection of G beta gamma subunits into oocytes directly induced release of intracellular Ca2+. We conclude that receptor coupling specificity of the G alpha q/G beta gamma heterotrimer is determined by G alpha q; G beta gamma is the predominant signaling molecule activating oocyte PLC beta.
Department of Pharmacology, Mayo Foundation, Rochester, Minnesota 55905, USA.
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Stehno-Bittel
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Krapivinsky
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Krapivinsky
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Perez-Terzic
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Clapham
D000109:Acetylcholine / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D005260:Female; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007668:Kidney; D046911:Macromolecular Substances; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D016376:Oligonucleotides, Antisense / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification; D037342:Pertussis Toxin; D011976:Receptors, Muscarinic / Q000096:biosynthesis / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014981:Xenopus
D007527:Isoenzymes; D046911:Macromolecular Substances; D009838:Oligodeoxyribonucleotides; D016376:Oligonucleotides, Antisense; D010446:Peptide Fragments; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D000109:Acetylcholine; D002118:Calcium