title: Glutamate 172, essential for modulation of L247T alpha7 ACh receptors by Ca2+, lines the extracellular vestibule.
abstract: Neuronal alpha7 nicotinic ACh receptors (nAChRs) are permeable to and modulated by Ca2+, Ba2+, and Sr2+. These permeant divalent cations interact with slowly desensitizing L247T alpha7 nAChRs to increase the potency and maximal efficacy of ACh, increase the efficacy of dihydro-beta-erythroidine (DHbetaE), and increase agonist-independent activity. Mutation of glutamate 172 (E172) to glutamine or cysteine eliminated these effects of permeant divalent cations. 2-(Trimethylammonium)ethyl methanethiosulfonate (MTSET), a cysteine-modifying reagent directed at water-accessible thiols, inhibited ACh-evoked currents of E172C/L247T alpha7 nAChRs by >90%, demonstrating that E172 was accessible to permeant ions. The data are consistent with a model of alpha7 receptors, derived from the crystal structure of the ACh binding protein (AChBP) from Lymnaea stagnalis, in which E172 projects toward the lumen of the extracellular vestibule. The observations that E172 was essential for divalent cation modulation of L247T alpha7 nAChRs and was accessible to permeating ions suggest that this residue participates in coupling ion permeation with modulation of receptor activity.
authors.affiliation: Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
authors.forename: Donnie
authors.initials: D
authors.lastname: Eddins
authors.forename: Adrian D
authors.initials: AD
authors.lastname: Sproul
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Lyford
authors.forename: James T
authors.initials: JT
authors.lastname: McLaughlin
authors.forename: Robert L
authors.initials: RL
authors.lastname: Rosenberg
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000493:pharmacokinetics; D002118:Calcium / Q000378:metabolism*; D003545:Cysteine / Q000235:genetics; D005110:Extracellular Space; D018698:Glutamic Acid / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D016296:Mutagenesis / Q000502:physiology; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D017434:Protein Structure, Tertiary; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D013324:Strontium / Q000493:pharmacokinetics; D014867:Water; D014982:Xenopus laevis; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D014867:Water; D001464:Barium; D018698:Glutamic Acid; D003545:Cysteine; D000109:Acetylcholine; D002118:Calcium; D013324:Strontium