title: Neuronal hyperactivity causes Na+/H+exchanger-induced extracellular acidification at active synapses.
abstract: Extracellular pH impacts on neuronal activity, which is in turn an important determinant of extracellular H+concentration. The aim of this study was to describe the spatio-temporal dynamics of extracellular pH at synaptic sites during neuronal hyperexcitability. To address this issue we created ex.E2GFP, a membrane-targeted extracellular ratiometric pH indicator that is exquisitely sensitive to acidic shifts. By monitoring ex.E2GFP fluorescence in real time in primary cortical neurons, we were able to quantify pH fluctuations during network hyperexcitability induced by convulsant drugs or high-frequency electrical stimulation. Sustained hyperactivity caused a pH decrease that was reversible upon silencing of neuronal activity and located at active synapses. This acidic shift was not attributable to the outflow of synaptic vesicle H+into the cleft nor to the activity of membrane-exposed H+V-ATPase, but rather to the activity of the Na+/H+-exchanger. Our data demonstrate that extracellular synaptic pH shifts take place during epileptic-like activity of neural cultures, emphasizing the strict links existing between synaptic activity and synaptic pH. This evidence may contribute to the understanding of the physio-pathological mechanisms associated with hyperexcitability in the epileptic brain.
authors.affiliation: Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.|Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy.
authors.forename: Martina
authors.initials: M
authors.lastname: Chiacchiaretta
authors.affiliation: Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.
authors.forename: Shahrzad
authors.initials: S
authors.lastname: Latifi
authors.affiliation: Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.
authors.forename: Mattia
authors.initials: M
authors.lastname: Bramini
authors.affiliation: Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy.
authors.forename: Manuela
authors.initials: M
authors.lastname: Fadda
authors.affiliation: Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.|Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Fassio
authors.affiliation: Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.|Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Benfenati
authors.affiliation: Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy fabrizia.cesca@iit.it.
authors.forename: Fabrizia
authors.identifier: 0000-0003-2190-6314
authors.initials: F
authors.lastname: Cesca
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002525:Cerebellar Cortex / Q000166:cytology*; D000071080:Cortical Excitability; D054351:Electrical Synapses / Q000378:metabolism*; D004827:Epilepsy / Q000503:physiopathology*; D005110:Extracellular Space; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008810:Mice, Inbred C57BL; D009431:Neural Conduction; D009474:Neurons / Q000502:physiology*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
chemical_list: D017923:Sodium-Hydrogen Exchangers; D000251:Adenosine Triphosphatases
keywords: Acidic pH; Active synapses; Experimental epilepsy; Na+/H+ exchanger; Neural hyperexcitability; PH-sensitive GFP