title: Conformational changes in the M2 muscarinic receptor induced by membrane voltage and agonist binding.
abstract: The ability to sense transmembrane voltage is a central feature of many membrane proteins, most notably voltage-gated ion channels. Gating current measurements provide valuable information on protein conformational changes induced by voltage. The recent observation that muscarinic G-protein-coupled receptors (GPCRs) generate gating currents confirms their intrinsic capacity to sense the membrane electrical field. Here, we studied the effect of voltage on agonist activation of M2 muscarinic receptors (M2R) in atrial myocytes and how agonist binding alters M2R gating currents. Membrane depolarization decreased the potency of acetylcholine (ACh), but increased the potency and efficacy of pilocarpine (Pilo), as measured by ACh-activated K+ current, I(KACh). Voltage-induced conformational changes in M2R were modified in a ligand-selective manner: ACh reduced gating charge displacement while Pilo increased the amount of charge displaced. Thus, these ligands manifest opposite voltage-dependent I(KACh) modulation and exert opposite effects on M2R gating charge displacement. Finally, mutations in the putative ligand binding site perturbed the movement of the M2R voltage sensor. Our data suggest that changes in voltage induce conformational changes in the ligand binding site that alter the agonist–receptor interaction in a ligand-dependent manner. Voltage-dependent GPCR modulation has important implications for cellular signalling in excitable tissues. Gating current measurement allows for the tracking of subtle conformational changes in the receptor that accompany agonist binding and changes in membrane voltage.
authors.affiliation: University Center for Biomedical Research, Universidad de Colima, Colima, México. magdal@ucol.mx
authors.forename: Ricardo A
authors.initials: RA
authors.lastname: Navarro-Polanco
authors.forename: Eloy G
authors.initials: EG
authors.lastname: Moreno Galindo
authors.forename: Tania
authors.initials: T
authors.lastname: Ferrer-Villada
authors.forename: Marcelo
authors.initials: M
authors.lastname: Arias
authors.forename: J Ryan
authors.initials: JR
authors.lastname: Rigby
authors.forename: José A
authors.initials: JA
authors.lastname: Sánchez-Chapula
authors.forename: Martin
authors.initials: M
authors.lastname: Tristani-Firouzi
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002415:Cats; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D008564:Membrane Potentials; D008958:Models, Molecular; D018721:Muscarinic Agonists / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010862:Pilocarpine / Q000494:pharmacology; D011487:Protein Conformation; D043585:Receptor, Muscarinic M2 / Q000819:agonists / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D018721:Muscarinic Agonists; D043585:Receptor, Muscarinic M2; D011994:Recombinant Proteins; D010862:Pilocarpine; D000109:Acetylcholine