During fast chemical synaptic transmission, neurotransmitter release is triggered by calcium (Ca2+) influx through voltage-gated Ca2+ channels (VGCCs) opened by an action potential (AP) at the nerve terminal. The magnitude and time course of neurotransmitter release is critically determined by the coupling between Ca2+ channels and synaptic vesicles. Studies of the quantitative dependence of transmitter release on the number of VGCCs provide important information for our understanding of the mechanisms that underlie the control and modulation of presynaptic release probability and kinetics. Using high-resolution calcium imaging techniques and variance analysis, I have determined the number of functional VGCCs within individual active zones (AZs) of the adult frog neuromuscular junction (NMJ) and their opening probability in response to single AP stimulation. The results have shown that the average number of VGCCs within individual active zones was relatively small (~28) and the average opening probability of individual Ca2+ channels during a presynaptic AP was very low (~0.24). Therefore, it is predicted that an action potential induced opening of relatively few Ca2+ channels in a single active zone. Furthermore, by combining pharmacological channel block, calcium imaging, postsynaptic recording, and 3D Monte Carlo diffusion-reaction simulations, I have studied the coupling of single Ca2+ channel openings to the triggering of vesicle fusion. I have provided evidence that Ca2+ entry through single open Ca2+ channels at the nerve terminal can be imaged directly and that such Ca2+ flux is sufficient to trigger synaptic vesicle fusion. I have further shown that following a single AP, the Ca2+ influx through a single open channel plays the predominant role in evoking neurotransmitter release, while Ca2+ ions derived from a collection of open Ca2+ channels are rarely required for vesicle exocytosis at this synapse.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-08132009-133311 |
| Date | 30 September 2009 |
| Creators | Luo, Fujun |
| Contributors | Stephen Meriney, Joel Stiles, Nathan Urban, Jon Johnson, Jen-Wei Lin, GuoQiang Bi |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-08132009-133311/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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