Muscarinic blockade of beta-adrenoceptor-stimulated adenylyl cyclase: the role of stimulatory and inhibitory guanine-nucleotide binding regulatory proteins (Gs and Gi)

N J Pyne, M W Grady, D Shehnaz, P A Stevens, S Pyne, I W Rodger

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Abstract

The functional antagonism that exists between muscarinic and beta-adrenoceptor function in guinea-pig tracheal smooth muscle was investigated by assessing Gs and Gi regulated adenylyl cyclase activity in isolated membranes. 2. Membranes from guinea-pig tracheal smooth muscle contain both Gi alpha and Gs alpha as assessed by Western blots with anti-G-protein antibodies. 3. GppNHp, a non-hydrolysable analogue of guanosine 5'-triphosphate (GTP), was shown to stimulate adenylyl cyclase activity at high concentrations (10(-6)-10(-4) M). GppNHp also produced a concentration-dependent reduction in pertussis toxin-catalysed adenosine diphosphate (ADP)-ribosylation of Gi alpha. 4. Pretreatment of tracheal smooth muscle slices with methacholine (10(-6) M) provoked a blockade of isoprenaline plus GTP, GppNHp- and GTP-stimulated adenylyl cyclase. 5. Addition of methacholine to membranes did not trigger inhibition of GTP-stimulated adenylyl cyclase activity but did block the isoprenaline-mediated augmentation of GTP-stimulated adenylyl cyclase activity. 6. Pretreatment of tracheal smooth muscle with methacholine (10(-6) M) provoked a blockade of cholera toxin-catalysed NAD(+)-dependent ADP-ribosylation of Gs alpha. 7. Phorbol-12-myristate 13-acetate (PMA)-treatment of tracheal smooth muscle slices actually enhanced GppNHp-stimulated adenylyl cyclase activity in subsequently prepared membranes. 8. We suggest that methacholine in addition to inhibiting adenylyl cyclase via a Gi-dependent mechanism induces a functional inactivation of Gs activity. These results together may explain the functional antagonism that exists between increased muscarinic tone and the ability of beta-adrenoceptor agonists to provoke excitation-contraction uncoupling.
Original languageEnglish
Pages (from-to)881-7
Number of pages7
JournalBritish Journal of Pharmacology
Volume107
Issue number3
Publication statusPublished - 1992

Keywords

  • adenylate cyclase
  • adrenergic beta-antagonists
  • animals
  • cholera toxin
  • GTP-binding proteins
  • guanylyl imidodiphosphate
  • guinea pigs
  • isoproterenol
  • membranes
  • methacholine compounds
  • muscle
  • parasympathomimetics
  • tetradecanoylphorbol acetate
  • trachea

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