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Ultrafast glutamate sensors resolve high-frequency release at Schaffer collateral synapses

Helassa, N; Durst, C; Coates, C; Kerruth, S; Arif, U; Schulze, C; Wiegert, JS; Geeves, M; Oertner, TG; Torok, K (2018) Ultrafast glutamate sensors resolve high-frequency release at Schaffer collateral synapses. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 115 (21). pp. 5594-5599. ISSN 0027-8424 https://doi.org/10.1073/pnas.1720648115
SGUL Authors: Torok, Katalin

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Abstract

Glutamatergic synapses display a rich repertoire of plasticity mechanisms on many different time scales, involving dynamic changes in the efficacy of transmitter release as well as changes in the number and function of postsynaptic glutamate receptors. The genetically encoded glutamate sensor iGluSnFR enables visualization of glutamate release from presynaptic terminals at frequencies up to ∼10 Hz. However, to resolve glutamate dynamics during high-frequency bursts, faster indicators are required. Here, we report the development of fast (iGluf) and ultrafast (iGluu) variants with comparable brightness but increased Kd for glutamate (137 μM and 600 μM, respectively). Compared with iGluSnFR, iGluu has a sixfold faster dissociation rate in vitro and fivefold faster kinetics in synapses. Fitting a three-state model to kinetic data, we identify the large conformational change after glutamate binding as the rate-limiting step. In rat hippocampal slice culture stimulated at 100 Hz, we find that iGluu is sufficiently fast to resolve individual glutamate release events, revealing that glutamate is rapidly cleared from the synaptic cleft. Depression of iGluu responses during 100-Hz trains correlates with depression of postsynaptic EPSPs, indicating that depression during high-frequency stimulation is purely presynaptic in origin. At individual boutons, the recovery from depression could be predicted from the amount of glutamate released on the second pulse (paired pulse facilitation/depression), demonstrating differential frequency-dependent filtering of spike trains at Schaffer collateral boutons.

Item Type: Article
Additional Information: Copyright © 2018 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND) (https://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: MD Multidisciplinary
SGUL Research Institute / Research Centre: Academic Structure > Molecular and Clinical Sciences Research Institute (MCS)
Journal or Publication Title: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
ISSN: 0027-8424
Dates:
DateEvent
22 May 2018Published
7 May 2018Published Online
17 April 2018Accepted
Publisher License: Publisher's own licence
Projects:
Project IDFunderFunder ID
BB/M02556X/1Biotechnology and Biological Sciences Research Councilhttp://dx.doi.org/10.13039/501100000268
094385/Z/10/ZWellcome Trusthttp://dx.doi.org/10.13039/100004440
SPP 1665German Research FoundationUNSPECIFIED
SFB 936German Research FoundationUNSPECIFIED
FOR 2419German Research FoundationUNSPECIFIED
SPP 1926German Research FoundationUNSPECIFIED
ERC-2016-StG 714762European Research Councilhttp://dx.doi.org/10.13039/501100000781
URI: https://openaccess.sgul.ac.uk/id/eprint/109780
Publisher's version: https://doi.org/10.1073/pnas.1720648115

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