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

Author(s): Momiyama, Akiko; Silver, Rachel A; Häusser, Michael A; Notomi, Takuya; Wu, Yue; Shigemoto, Ryuichi; Cull-Candy, Stuart G
Article Title: The density of AMPA receptors activated by a transmitter quantum at the climbing fibre - Purkinje cell synapse in immature rats
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 ∼300 pS. Peak-scaled non-stationary fluctuation analysis of spontaneous EPSCs and MEPSCs gave a weighted-mean synaptic channel conductance of ∼5 pS (∼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 (∼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 μm2, 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 ∼900 μm-2 in the postsynaptic membrane.
Keywords: Glutamate receptor; Glutamic Acid; AMPA receptor; lpha amino 3 hydroxy 5 methyl 4 isoxazolepropionic acid; protein subunit; receptor antibody
Journal Title: Journal of Physiology
Volume: 549
Issue 1
ISSN: 1469-7793
Publisher: Wiley-Blackwell  
Date Published: 2003-05-15
Start Page: 75
End Page: 92
DOI: 10.1113/jphysiol.2002.033472
Open access: no