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The Startle disease mutation, α1S270T, predicts shortening of glycinergic synaptic currents

Wu, Z; Lape, R; Jopp-Saile, L; O'Callaghan, BJ; Greiner, T; Sivilotti, LG; (2020) The Startle disease mutation, α1S270T, predicts shortening of glycinergic synaptic currents. The Journal of Physiology , 598 (16) pp. 3417-3438. 10.1113/JP279803. Green open access

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Abstract

KEY POINTS: Loss-of-function mutations in proteins found at glycinergic synapses, most commonly in the α1 subunit of the glycine receptor (GlyR), cause the startle disease/hyperekplexia channelopathy in man. It was recently proposed that the receptors responsible are presynaptic homomeric GlyRs, rather than postsynaptic heteromeric GlyRs (which mediate glycinergic synaptic transmission), because heteromeric GlyRs are less affected by many startle mutations than homomers. We examined the α1 startle mutation S270T, at the extracellular end of the M2 transmembrane helix. Recombinant heteromeric GlyRs were less impaired than homomers by this mutation when we measured their response to equilibrium applications of glycine. However, currents elicited by synaptic-like millisecond applications of glycine to outside-out patches were much shorter (7- to 10-fold) in all mutant receptors, both homomeric and heteromeric. Thus the synaptic function of heteromeric receptors is likely to be impaired by the mutation. ABSTRACT: Human startle disease is caused by mutations in glycine receptor (GlyR) subunits or in other proteins associated with glycinergic synapses. Many startle mutations are known, but it is hard to correlate the degree of impairment at molecular level with the severity of symptoms in patients. It was recently proposed that the disease is caused by disruption in the function of presynaptic homomeric GlyRs (rather than postsynaptic heteromeric GlyRs), because homomeric GlyRs are more sensitive to loss-of-function mutations than heteromers. Our patch-clamp recordings from heterologously-expressed GlyR characterised in detail the functional consequences of the α1S270T startle mutation, which is located at the extracellular end of the pore lining M2 transmembrane segment (18'). This mutation profoundly decreased the maximum single-channel open probability of homomeric GlyR (to 0.16; cf. 0.99 for wild-type) but reduced only marginally that of heteromeric GlyR (0.96; cf. 0.99 for wild-type). However, both heteromeric and homomeric mutant GlyR became less sensitive to the neurotransmitter glycine. Responses evoked by brief, quasi-synaptic pulses of glycine onto outside-out patches were impaired in mutant receptors, as deactivation was approximately 10- and 7-fold faster for homomeric and heteromeric GlyRs, respectively. Our data suggest that the α1S270T mutation is likely to affect the opening step in GlyR activation. The faster decay of synaptic currents mediated by mutant heteromeric GlyRs is expected to reduce charge transfer at the synapse, despite the high equilibrium open probability of these mutant channels. This article is protected by copyright. All rights reserved.

Type: Article
Title: The Startle disease mutation, α1S270T, predicts shortening of glycinergic synaptic currents
Location: England
Open access status: An open access version is available from UCL Discovery
DOI: 10.1113/JP279803
Publisher version: http://dx.doi.org/10.1113/JP279803
Language: English
Additional information: © 2020 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Keywords: glycine receptors, human channelopathy, patch-clamp, single channel recording
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Neuro, Physiology and Pharmacology
URI: https://discovery.ucl.ac.uk/id/eprint/10098596
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