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

J Physiol. 2003 May 15;549(Pt 1):75-92. doi: 10.1113/jphysiol.2002.033472. Epub 2003 Mar 28.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Age Factors
  • Animals
  • Cerebellum / cytology
  • Cerebellum / growth & development
  • Cerebellum / physiology
  • Excitatory Postsynaptic Potentials / physiology
  • Ion Channel Gating / physiology
  • Microscopy, Immunoelectron
  • Nerve Fibers / chemistry
  • Nerve Fibers / physiology
  • Nerve Fibers / ultrastructure
  • Neuronal Plasticity / physiology
  • Organ Culture Techniques
  • Purkinje Cells / chemistry
  • Purkinje Cells / cytology
  • Purkinje Cells / physiology*
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, AMPA / analysis
  • Receptors, AMPA / physiology*
  • Synapses / chemistry
  • Synapses / physiology*
  • Synapses / ultrastructure


  • Receptors, AMPA
  • glutamate receptor ionotropic, AMPA 3
  • glutamate receptor ionotropic, AMPA 2