Quantal amplitude at the cone ribbon synapse can be adjusted by changes in cytosolic glutamate

Theodore M. Bartoletti, Wallace B Thoreson

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Purpose: Vision is encoded at photoreceptor synapses by the number of released vesicles and size of the post-synaptic response. We hypothesized that elevating cytosolic glutamate could enhance quantal size by increasing glutamate in vesicles. Methods: We introduced glutamate (10-40 mM) into cone terminals through a patch pipette and recorded excitatory postsynaptic currents (EPSCs) from horizontal or OFF bipolar cells in the Ambystoma tigrinum retinal slice preparation. Results: Elevating cytosolic glutamate in cone terminals enhanced EPSCs as well as quantal miniature EPSCs (mEPSCs). Enhancement was prevented by inhibiting vesicular glutamate transport with 1S,3R-1-aminocyclopentane-1,3- dicarboxylate in the patch pipette. A low affinity glutamate receptor antagonist, γD-glutamylglycine (1 mM), less effectively inhibited EPSCs evoked from cones loaded with glutamate than control cones indicating that release from cones with supplemental glutamate produced higher glutamate levels in the synaptic cleft. Raising presynaptic glutamate did not alter exocytotic capacitance responses and exocytosis was observed after inhibiting glutamate loading with the vesicular ATPase inhibitor, concanamycin A, suggesting that release capability is not restricted by low vesicular glutamate levels. Variance-mean analysis of currents evoked by flash photolysis of caged glutamate indicated that horizontal cell AMPA receptors have a single channel conductance of 10.1 pS suggesting that ~8.7 GluRs contribute to each mEPSC. Conclusions: Quantal amplitude at the cone ribbon synapse is capable of adjustment by changes in cytosolic glutamate levels. The small number of channels contributing to each mEPSC suggests that stochastic variability in channel opening could be an important source of quantal variability.

Original languageEnglish (US)
Pages (from-to)920-931
Number of pages12
JournalMolecular Vision
Volume17
StatePublished - May 9 2011

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Synapses
Glutamic Acid
Excitatory Postsynaptic Potentials
Ambystoma
Social Adjustment
Excitatory Amino Acid Antagonists
AMPA Receptors
Photolysis
Exocytosis
Adenosine Triphosphatases
Analysis of Variance

ASJC Scopus subject areas

  • Ophthalmology

Cite this

Quantal amplitude at the cone ribbon synapse can be adjusted by changes in cytosolic glutamate. / Bartoletti, Theodore M.; Thoreson, Wallace B.

In: Molecular Vision, Vol. 17, 09.05.2011, p. 920-931.

Research output: Contribution to journalArticle

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