Biophysical Society Thematic Meeting| Padova 2019

Quantitative Aspects of Membrane Fusion and Fission

Wednesday Speaker Abstracts

COMPARISON OF THE TRANSMITTER RELEASE PROPERTIES BETWEEN THE CALYX OF HELD SYNAPSE AND MOSSY FIBER-CA3 SYNAPSE Takeshi Sakaba 1 ; 1 Doshisha University, Kyotanabe, Kyoto, Japan Calyx of Held synapses are known as one of the model synapses in the mammalian CNS, and exhibit short-term depression during repetitive stimulation. In contrast, hippocampal mossy fiber synapses show pronounced facilitation during repetitive stimulation and exhibit various forms of long-term synaptic plasticity. Biophysical analysis of this synapse-type remains to be carried out.To investigate the mechanism of transmitter release and presynaptic modulation at the mossy fiber synapse, we used presynaptic capacitance measurements and postsynaptic recording to measure the transmitter release kinetics. In addition, total internal reflection fluorescence (TIRF) microscopy was used to visualize dynamics of single synaptic vesicles near the plasma membrane. Readily releasable synaptic vesicles are mediated by fusion of already-tethered vesicles within the TIRF field. Vesicle replenishment had fast and slow phases. The fast phase of vesicle replenishment likely depends on synaptic vesicle priming from already-tethered vesicles rather than synaptic vesicle tethering toward the release sites. cAMP, a molecule crucial for short and long-term plasticity, mainly increases the vesicular release probability without changing the number of readily-releasable synaptic vesicles, cAMP possibly increased the release probability by changing the (spatial) coupling between Ca 2+ channels and synaptic vesicles. We compared these findings, such as basic release properties and their modulation by second messengers, with those obtained at the calyx of Held synapse, and discussed similarities and differences between two synapse types. Supported by JSPS/MEXT KAKENHI grants (18H02530/17H05753) and the JSPS Core-to-Core program A. Advanced Research Networks.

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