Title : Muscarinic blockade of beta-adrenoceptor-stimulated adenylyl cyclase: the role of stimulatory and inhibitory guanine-nucleotide binding regulatory proteins (Gs and Gi) - Pyne_1992_Br.J.Pharmacol_107_881 |
Author(s) : Pyne NJ , Grady MW , Shehnaz D , Stevens PA , Pyne S , Rodger IW |
Ref : British Journal of Pharmacology , 107 :881 , 1992 |
Abstract :
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. |
PubMedSearch : Pyne_1992_Br.J.Pharmacol_107_881 |
PubMedID: 1361873 |
Pyne NJ, Grady MW, Shehnaz D, Stevens PA, Pyne S, Rodger IW (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 :881
Pyne NJ, Grady MW, Shehnaz D, Stevens PA, Pyne S, Rodger IW (1992)
British Journal of Pharmacology
107 :881