title: cGMP-mediated inhibition of cardiac L-type Ca(2+) current by a monoclonal antibody against the M(2) ACh receptor.
abstract: The effects of a monoclonal antibody (B8E5) directed against the second extracellular loop of the muscarinic M(2) receptor were studied on the L-type Ca(2+) currents (I(Ca,L)) of guinea pig ventricular myocytes using the whole cell patch-clamp technique. Similar to carbachol, B8E5 reduced the isoproterenol (ISO)-stimulated I(Ca,L) but did not significantly affect basal I(Ca,L). Atropine blocked the inhibitory effect of B8E5. The electrophysiological parameters of ISO-stimulated I(Ca,L) were not modified in presence of B8E5. Inhibition of I(Ca,L) by B8E5 was still observed when intracellular cAMP was either enhanced by forskolin or maintained constant by using a hydrolysis-resistant cAMP analog (8-bromoadenosine 3',5'-cyclic monophosphate) or by applying the phosphodiesterase inhibitor IBMX. The effect of B8E5 was mimicked by 8-bromoguanosine 3',5'-cyclic monophosphate, a potent stimulator of cGMP-dependent protein kinase, and prevented by a selective inhibitor of nitric oxide-sensitive guanylyl cyclase [1H-(1,2,4)oxadiazolo[4,3-a]quinoxaline-1-one]. These results indicate that the antibody B8E5 inhibits the beta-adrenergic-stimulated I(Ca,L) through activation of the M(2) muscarinic receptor and further suggest that the antibody acts not via the classical pathway of decreasing intracellular cAMP, but rather by increasing cGMP.
authors.affiliation: Instituto de Biofisica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, 21949-900 Rio de Janeiro, Brazil. jhmn@biof.ufrj.br
authors.forename: J H
authors.initials: JH
authors.lastname: Nascimento
authors.forename: L
authors.initials: L
authors.lastname: Sallé
authors.forename: J
authors.initials: J
authors.lastname: Hoebeke
authors.forename: J
authors.initials: J
authors.lastname: Argibay
authors.forename: N
authors.initials: N
authors.lastname: Peineau
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D001323:Autoantibodies; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D006152:Cyclic GMP / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006151:Guanosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000166:cytology; D010069:Oxadiazoles / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic / Q000276:immunology* / Q000378:metabolism*
chemical_list: C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D000318:Adrenergic beta-Agonists; D000911:Antibodies, Monoclonal; D001323:Autoantibodies; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D010069:Oxadiazoles; D010726:Phosphodiesterase Inhibitors; D011810:Quinoxalines; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic; D006151:Guanosine; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; C035169:8-bromoguanosine; D006152:Cyclic GMP; D007545:Isoproterenol; D015056:1-Methyl-3-isobutylxanthine