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The density of AMPA receptors activated by a transmitter quantum at the climbing fibre‐Purkinje cell synapse in immature rats
Author(s) -
Momiyama Akiko,
Silver R. Angus,
Häusser Michael,
Notomi Takuya,
Wu Yue,
Shigemoto Ryuichi,
CullCandy Stuart G.
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2002.033472
Subject(s) - ampa receptor , excitatory postsynaptic potential , synapse , postsynaptic potential , conductance , neuroscience , purkinje cell , biophysics , glutamate receptor , neurotransmission , postsynaptic density , chemistry , physics , cerebellum , biology , receptor , biochemistry , inhibitory postsynaptic potential , condensed matter physics
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 m m ), we also obtained a small single‐channel conductance estimate for extrasynaptic AMPARs (∼11 pS). This approach allowed us to obtain a maximum open probability ( P o,max ) value for the extrasynaptic receptors ( P o,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 μm 2 , 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.