title: Na+/H+exchange via the Drosophila vesicular glutamate transporter mediates activity-induced acid efflux from presynaptic terminals.
abstract: Intracellular pH regulation is vital to neurons as nerve activity produces large and rapid acid loads in presynaptic terminals. Rapid clearance of acid loads is necessary to maintain control of neurotransmission, but neuronal acid clearance mechanisms remain poorly understood. Glutamate is loaded into synaptic vesicles via the vesicular glutamate transporter (VGLUT), a mechanism conserved across phyla, and this study reports a previously unknown role for VGLUT as an acid-extruding protein when deposited in the plasmamembrane during exocytosis. The finding was made in Drosophila (fruit fly) larval motor neurons through a combined pharamacological and genetic dissection of presynaptic pH homeostatic mechanisms. A dual role for VGLUT serves to integrate neuronal activity and pH regulation in presynaptic nerve terminals.
  
  
  
  Neuronal activity can result in transient acidification of presynaptic terminals, and such shifts in cytosolic pH (pHcyto) probably influence mechanisms underlying forms of synaptic plasticity with a presynaptic locus. As neuronal activity drives acid loading in presynaptic terminals, we hypothesized that the same activity might drive acid efflux mechanisms to maintain pHcytohomeostasis. To better understand the integration of neuronal activity and pHcytoregulation we investigated the acid extrusion mechanisms at Drosophila glutamatergic motorneuron terminals. Expression of a fluorescent genetically encoded pH indicator, named 'pHerry', in the presynaptic cytosol revealed acid efflux following nerve activity to be greater than that predicted from measurements of the intrinsic rate of acid efflux. Analysis of activity-induced acid transients in terminals deficient in either endocytosis or exocytosis revealed an acid efflux mechanism reliant upon synaptic vesicle exocytosis. Pharmacological and genetic dissection in situ and in a heterologous expression system indicate that this acid efflux is mediated by conventional plasmamembrane acid transporters, and also by previously unrecognized intrinsic H+/Na+exchange via the Drosophila vesicular glutamate transporter (DVGLUT). DVGLUT functions not only as a vesicular glutamate transporter but also serves as an acid-extruding protein when deposited on the plasmamembrane.
authors.affiliation: School of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX, 78229, USA.
authors.forename: Adam J
authors.identifier: 0000-0001-8959-106X
authors.initials: AJ
authors.lastname: Rossano
authors.affiliation: Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8503, Japan.|Physiology & Biomedical Engineering and Nephrology & Hypertension, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA.
authors.forename: Akira
authors.initials: A
authors.lastname: Kato
authors.affiliation: Biological Sciences & Wilkes Honors College, Florida Atlantic University, Jupiter, FL, 33431, USA.
authors.forename: Karyl I
authors.initials: KI
authors.lastname: Minard
authors.affiliation: Physiology & Biomedical Engineering and Nephrology & Hypertension, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Romero
authors.affiliation: Biological Sciences & Wilkes Honors College, Florida Atlantic University, Jupiter, FL, 33431, USA.
authors.forename: Gregory T
authors.initials: GT
authors.lastname: Macleod
mesh_terms: D000818:Animals; D003600:Cytosol / Q000502:physiology; D004330:Drosophila; D006859:Hydrogen / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007814:Larva; D009046:Motor Neurons / Q000502:physiology*; D009865:Oocytes; D017729:Presynaptic Terminals / Q000502:physiology*; D012964:Sodium / Q000502:physiology; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology; D050496:Vesicular Glutamate Transport Proteins / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: D017923:Sodium-Hydrogen Exchangers; D050496:Vesicular Glutamate Transport Proteins; D006859:Hydrogen; D012964:Sodium
keywords: ion transport; motor nerve terminal; pH regulation