Transmitter Release from Mammalian Horizontal Cells

光感受器突触三联体是非常重要的突触复合体;生理上，这是光感受器突触三联体的位点。 视觉信息的初始传递，以及信息传递的保真度对视觉至关重要。 处理.突触三联体的特征在于感光体末端、ON-双极细胞树突和 横向分布的水平细胞突起。水平细胞在产生抑制性细胞中起着重要作用。 光感受器和双极细胞以及其他下游视网膜神经元的感受场周围。 水平细胞参与光适应、中心-周围感受野的形成和细胞周期的产生。 视网膜神经元的颜色变化。囊泡介导的递质释放和质子分泌是导致 候选人潜在的水平细胞输出在外层视网膜，虽然细胞机制和他们的 作用地点尚未完全了解。 该项目的长期目标是了解哺乳动物水平细胞在视觉系统中的作用。 信息处理.这一目标将通过检验以下假设来实现：1）受监管的 囊泡机制是水平细胞突起释放GABA和分泌质子的基础， 它们的末端，和2）水平细胞通过VATP酶参与对光感受器的pH敏感作用， 和水平和双极细胞上的抑制性GABA作用。具体目标1将测试a） 囊泡与质膜的融合是Ca 2+依赖性的，并决定B）细胞定位和 在水平细胞中介导Ca 2+信号传导的Ca 2+通道亚型的功能特性。具体目标2 将测试a）囊泡与质膜的融合是否是SNARE蛋白依赖性的，并确定B） 介导囊泡胞吐作用的关键囊泡和SNARE蛋白的细胞定位和结合伴侣， 包括V-ATP酶。具体目标3将测试水平细胞囊泡胞吐是否介导 a）通过V-ATP酶插入突触囊泡和血浆对光感受器的pH敏感作用 膜和B）GABA作用于水平和双极细胞。实验将a）评估V-ATP酶活性 在水平细胞末梢中，B）确定pH敏感水平细胞作用是否由V-ATP酶介导 依赖性质子和/或其它pH调节膜蛋白，和c）确定GABA是否介导 水平细胞自分泌和双极细胞前馈作用。使用形态学、电生理学 和细胞成像方法将初步阐明受调节的囊泡的分子和细胞基础， 释放和质子分泌水平细胞，并将决定水平细胞的反应行动 外视网膜神经元的特性。

The photoreceptor synapse triad is a synaptic complex of great importance; physiologically, this is the site of the initial transfer of visual information, and the fidelity of information transfer is critically important for visual processing. The synaptic triad is characterized by the photoreceptor terminal, ON-bipolar cell dendrite and laterally distributed horizontal cell processes. Horizontal cells play a central role in generating the inhibitory receptive-field surrounds of photoreceptors and bipolar cells, as well as other, downstream retinal neurons. Horizontal cells participate in light adaptation, formation of center-surround receptive fields and generation of color opponency in retinal neurons. Vesicular-mediated transmitter release and proton secretion are leading candidates underlying horizontal cell output in the outer retina, although the cellular mechanisms and their sites of action are not yet fully understood. The long-term objective of this program is to understand the role of mammalian horizontal cells in visual information processing. This objective will be addressed by testing the hypotheses that 1) a regulated vesicular mechanism underlies GABA release and proton secretion from horizontal cell processes and their endings, and 2) horizontal cells participate in a pH-sensitive action on photoreceptors via VATPase, and an inhibitory GABA action on horizontal and bipolar cells. Specific aim 1 will test if a) vesicle fusion with the plasma membrane is Ca2+-dependent, and determine the b) cellular localization and functional properties of the Ca2+ channel subtypes mediating Ca2+ signaling in horizontal cells. Specific aim 2 will test if a) vesicle fusion with the plasma membrane is SNARE-protein dependent, and determine the b) cellular localization and binding partners of key vesicular and SNARE proteins mediating vesicle exocytosis, including V-ATPase, in horizontal cells. Specific aim 3 will test if horizontal cell vesicular exocytosis mediates a) a pH-sensitive action on photoreceptors via V-ATPase insertion into the synaptic vesicle and plasma membrane and b) GABA action at horizontal and bipolar cells. Experiments will a) evaluate V-ATPase activity in horizontal cell endings, b) determine if pH-sensitive horizontal cell action is mediated by V-ATPase dependent protons and/or other pH-regulating membrane proteins and c) determine if GABA mediates horizontal cell autocrine and bipolar cell feed forward action. Studies using morphological, electrophysiological and cellular imaging approaches will initially elucidate the molecular and cellular basis of regulated vesicular release and proton secretion from horizontal cells, and will determine horizontal cell action on the response properties of outer retinal neurons.