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

Br J Pharmacol. 1992 Nov;107(3):881-7. doi: 10.1111/j.1476-5381.1992.tb14541.x.


1. 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenylyl Cyclases / metabolism*
  • Adrenergic beta-Antagonists / pharmacology*
  • Animals
  • Blotting, Western
  • Cholera Toxin / pharmacology
  • GTP-Binding Proteins / metabolism*
  • Guanylyl Imidodiphosphate / pharmacology
  • Guinea Pigs
  • In Vitro Techniques
  • Isoproterenol / pharmacology
  • Membranes / drug effects
  • Methacholine Compounds / pharmacology
  • Muscle, Smooth / drug effects
  • Parasympathomimetics / pharmacology*
  • Tetradecanoylphorbol Acetate / pharmacology
  • Trachea / drug effects


  • Adrenergic beta-Antagonists
  • Methacholine Compounds
  • Parasympathomimetics
  • Guanylyl Imidodiphosphate
  • Cholera Toxin
  • GTP-Binding Proteins
  • Adenylyl Cyclases
  • Isoproterenol
  • Tetradecanoylphorbol Acetate