Pyne, N J and Grady, M W and Shehnaz, D and Stevens, P A and Pyne, S and Rodger, I W (1992) Muscarinic blockade of beta-adrenoceptor-stimulated adenylyl cyclase: the role of stimulatory and inhibitory guanine-nucleotide binding regulatory proteins (Gs and Gi). British Journal of Pharmacology, 107 (3). pp. 881-7. ISSN 0007-1188Full text not available in this repository. (Request a copy from the Strathclyde author)
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.
|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, Therapeutics. Pharmacology, Pharmacology|
|Subjects:||Medicine > Therapeutics. Pharmacology|
|Department:||Faculty of Science > Strathclyde Institute of Pharmacy and Biomedical Sciences|
|Depositing user:||Pure Administrator|
|Date Deposited:||15 Nov 2011 05:18|
|Last modified:||04 May 2016 20:20|