The Origin of Quantal Size Variation: Vesicular Glutamate Concentration Plays a Significant Role

• DOI: 10.1523/jneurosci.4415-06.2007
• Publication Date: 2007-03-14T16:11:09Z
• Authors: Xin-Sheng Wu; Lei Xue; Raja Mohan; Kenneth Paradiso; Kevin D. Gillis; Ling-Gang Wu
• Keywords: Postsynaptic Current

Fusion of a single vesicle induces quantal response, which is critical in determining synaptic strength. Quantal size varies at most synapses. Its underlying mechanisms are not well understood. Here, we examined five sources variation: vesicular glutamate concentration ([Glu] v ), volume, ultrafast fusion pore closure, the postsynaptic receptor, and location between release receptor cluster glutamatergic, calyx Held By averaging 2.66 million events from 459 synapses, resolved capacitance jump evoked by fusion. This jump, an indicator was independent amplitude miniature EPSC (mEPSC) recorded simultaneously same Thus, volume main source mEPSC variation. The followed submillisecond endocytosis, excluding endocytosis as Larger mEPSCs were increased to lesser extent presynaptic dialysis, reduced γ-DGG (γ- d -glutamylglycine), competitive AMPA blocker, suggesting that higher cleft contributes large mEPSCs. accompanied briefer rise times, inconsistent with prediction by, thus arguing against, scenario larger caused shorter distance site cluster. In summary, different amplitudes mainly attributable vesicles having similar volumes, but amounts, [Glu]