Calcium Triggered Synaptic Vesicle Exocytosis

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Title: Calcium Triggered Synaptic Vesicle Exocytosis
Author: Pang, Zhiping
Abstract: Neurotransmitter release is triggered by the action potential induced influx of Ca 2+ into nerve terminals . One of the central questions in neuroscience is how Ca 2+ promotes synaptic vesicles from rest to fusion leading to release of neurotransmitters . In this thesis , I first addressed if synaptogmin -1 /SNARE binding is important for synaptic vesicle release . Using two knock -in mouse lines each with single amino -acid substitution , namely D232N and D238N in synaptotagmin -1 , combined with electrophysiology , I found evoked release in D232N mutant neuronal cultures is significantly increased , whereas in D238N cultures release is slightly but significantly decreased . Ca 2+ titration curves indicated the apparent Ca 2+ -affinity for vesicle release significantly increased in D232N synapses . These data are consistent with biochemical studies that showed that the D232N substitution in synaptotagmin -1 increases Ca 2+ -dependent SNARE bindings but leaves phospholipid binding unchanged , whereas the D238N mutant slightly decreased phospholipid binding but leaves SNARE binding insignificantly changed . Second , I addressed if synaptotamgin -2 is another Ca 2+ -sensor for synaptic vesicle release . I and my colleagues used two mouse lines : one contains a single amino acid mutation in synaptotagmin -2 (I377N ) and one has synaptotagmin -2 ablated from the genome . By using a combination of biophysical , biochemical and functional techniques , we determined that synaptotagmin -2 is a fast synchronous Ca 2+ -sensor . Third , in collaboration with Jianyuan Sun , we explored the biophysical properties of the slow Ca 2+ -sensor in the Calyx of Held . Using Ca 2+ -uncaging combined with electrophysiology , we mapped increasing Ca 2+ concentrations in relation to neurotransmitter release and built a comprehensive mathematical model for the Ca 2+ control of synaptic vesicle fusion . We found compelling evidence for the existence of two Ca 2+ - sensors : one (synaptotagmin -2 in the Calyx of Held ) is responsible for fast synchronous release , and the other one is responsible for slow delayed synaptic release . Surprisingly , we found the two Ca 2+ -sensors have similar apparent Ca 2+ affinities . This study showed clearly that synaptotagmin -2 is a fast Ca 2+ -sensor , and gave us a prediction that narrows down the potential candidate for the slow Ca 2+ -sensor .
URI: http : / /hdl .handle .net /2152 .5 /643
Date: 2007-08-08

Citation

Calcium Triggered Synaptic Vesicle Exocytosis. Graduate School of Biomedical Sciences. Available electronically from http : / /hdl .handle .net /2152 .5 /643 .

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