The density of AMPA receptors activated by a transmitter quantum at the climbing fibre-Purkinje cell synapse in immature rats.

Full Abstract

We aimed to estimate the number of AMPA receptors (AMPARs) bound by the quantal transmitter packet, their single-channel conductance and their density in the postsynaptic membrane at cerebellar Purkinje cell synapses. The synaptic and extrasynaptic AMPARs were examined in Purkinje cells in 2- to 4-day-old rats, when they receive synaptic inputs solely from climbing fibres (CFs). Evoked CF EPSCs and whole-cell AMPA currents displayed roughly linear current-voltage relationships, consistent with the presence of GluR2 subunits in synaptic and extrasynaptic AMPARs. The mean quantal size, estimated from the miniature EPSCs (MEPSCs), was approximately 300 pS. Peak-scaled non-stationary fluctuation analysis of spontaneous EPSCs and MEPSCs gave a weighted-mean synaptic channel conductance of approximately 5 pS (approximately 7 pS when corrected for filtering). By applying non-stationary fluctuation analysis to extrasynaptic currents activated by brief glutamate pulses (5 mM), we also obtained a small single-channel conductance estimate for extrasynaptic AMPARs (approximately 11 pS). This approach allowed us to obtain a maximum open probability (Po,max) value for the extrasynaptic receptors (Po,max = 0.72). Directly resolved extrasynaptic channel openings in the continued presence of glutamate exhibited clear multiple-conductance levels. The mean area of the postsynaptic density (PSD) of these synapses was 0.074 microm2, measured by reconstructing electron-microscopic (EM) serial sections. Postembedding immunogold labelling by anti-GluR2/3 antibody revealed that AMPARs are localised in PSDs. From these data and by simulating error factors, we estimate that at least 66 AMPARs are bound by a quantal transmitter packet at CF-Purkinje cell synapses, and the receptors are packed at a minimum density of approximately 900 microm-2 in the postsynaptic membrane.

Author information

Author/s: Momiyama, Akiko (A); Silver, R Angus (RA); Hausser, Michael (M); Notomi, Takuya (T); Wu, Yue (Y); Shigemoto, Ryuichi (R); Cull-Candy, Stuart G (SG);

Affiliation: Department of Pharmacology, University College London, UK. amomiyam(-atsign-)nips.ac.jp

Journal and publication information

Publication Type: Journal Article; Research Support, Non-U.S. Gov't

Journal: The Journal of physiology (J Physiol), published in England. (Language: eng)

Reference: 2003-May; vol 549 (issue Pt 1) : pp 75-92

Dates: Created 2003/05/15; Completed 2004/01/16; Revised 2008/11/20;

PMID: 12665613, status: MEDLINE (last retrieval date: 2/18/2009, IMS Date: )

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