MOLECULAR MECHANISMS OF TRANSMITTER RELEASE

本研究项目的目的是与法国研究小组合作，阐明神经递质释放的分子机制。这些研究集中在1)囊泡募集和启动的机制，2)囊泡对钙信号的响应融合的机制，我们得到了以下结果。囊泡募集和启动的机制1)我们认为，肌醇多磷酸与突触素C2结构域的结合对胞吐起抑制作用。我们阐明了嗜铬细胞中结合的肌醇多磷酸与突触素的解离是对钙离子的反应。显微注射肌醇六氢磷酸可抑制诱发的和自发的胞吐作用，但不能抑制胞吐。2)我们阐明肌动蛋白网络和肌动蛋白-肌球蛋白相互作用是囊泡募集和启动所必需的。我们还发现，蛋白激酶C的易化作用是通过激活的蛋白激酶Cα或蛋白激酶Cβ、其受体分子RACK1和皮质F-肌动蛋白之间的复合体来实现的。2)突触传递的研究阐明了SNARE蛋白的再循环和SNARE蛋白与N型钙通道的结合。还发现Doc2α与Munc13-1的结合先于胞吐作用。

The aim of this research project is to elucidate the molecular mechanism of neurotransmitter release in collaboration with French group. The studies focused on 1) the mechanism of vesicle recruitment and priming, 2) the mechanism of fusion of vesicles in response to Ca^<2+> signals, and we have obtained the following results.1. The mechanism of vesicle recruitment and priming.1) We have suggested that binding of inositol polyphosphates to C2 domain of synaptotagmin acts as an inhibitory clamp for the exocytosis. We clarified that the bound inositol polyphosphates dissociate from synaptotagmin in response to Ca^<2+> in chromaffin cells. Microinjected inositol hexakisphosphate inhibited both the evoked and spontaneous exocytosis, while inositol hexakissulfate failed to inhibit.2) We clarified that the subplasmalemmal actin network and actin-myosin interaction are essential for the vesicle recruitment and priming. We also found that the facilitation of the priming by protein kinase C (PKC) is mediated through the complex between the activated PKC α or PKC β, their receptor molecule RACK1 and cortical F-actin.2. The mechanism of fusion of vesicles in response to Ca^<2+> signals.1) Studies with subclones of PC12 cells demonstrated that the reduced expression of syntaxin, VAMP-2, SNAP-25 and Munc-18 decreased the exocytotic activity.2) Studies on synaptic transmission clarified the recycle of SNARE proteins and binding of SNARE proteins with N-type Ca^<2+>-channels. It was also found that binding of Doc2 α to Munc13-1 precedes exocytosis.