Format

Send to

Choose Destination
Proc Natl Acad Sci U S A. 2018 May 22;115(21):5594-5599. doi: 10.1073/pnas.1720648115. Epub 2018 May 7.

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

Author information

1
Molecular and Clinical Sciences Research Institute, St George's, University of London, SW17 0RE London, United Kingdom.
2
Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg, 20251 Hamburg, Germany.
3
School of Biosciences, University of Kent, CT2 7NZ Canterbury, United Kingdom.
4
Molecular and Clinical Sciences Research Institute, St George's, University of London, SW17 0RE London, United Kingdom; k.torok@sgul.ac.uk.

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 (iGlu f ) and ultrafast (iGlu u ) variants with comparable brightness but increased Kd for glutamate (137 μM and 600 μM, respectively). Compared with iGluSnFR, iGlu u 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 iGlu u is sufficiently fast to resolve individual glutamate release events, revealing that glutamate is rapidly cleared from the synaptic cleft. Depression of iGlu u 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.

KEYWORDS:

glutamate; hippocampus; synaptic transmission; two-photon imaging

PMID:
29735711
DOI:
10.1073/pnas.1720648115
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center