LoGiudice Lisamarie, Matthews Gary
Program in Neuroscience, Department of Neurobiology and Behavior, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.
Traffic. 2007 Sep;8(9):1123-8. doi: 10.1111/j.1600-0854.2007.00591.x. Epub 2007 Jun 5.
Unlike conventional synaptic terminals that release neurotransmitter episodically in response to action potentials, neurons of the visual, auditory and vestibular systems encode sensory information in graded signals that are transmitted at their synapses by modulating the rate of continuous release. The synaptic ribbon, a specialized structure found at the active zones of these neurons, is necessary to sustain the high rates of exocytosis required for continuous release. To maintain the fidelity of synaptic transmission, exocytosis must be balanced by high-capacity endocytosis, to retrieve excess membrane inserted during vesicle fusion. Capacitance measurements following vesicle release in ribbon-type neurons indicate two kinetically distinct phases of compensatory endocytosis, whose relative contributions vary with stimulus intensity. The two phases can be independently regulated and may reflect different underlying mechanisms operating on separate pools of recycling vesicles. Electron microscopy shows diversity among ribbon-type synapses in the relative importance of clathrin-mediated endocytosis versus bulk membrane retrieval as mechanisms of compensatory endocytosis. Ribbon synapses, like conventional synapses, make use of multiple endocytosis pathways to replenish synaptic vesicle pools, depending on the physiological needs of the particular cell type.
与传统突触终端不同，传统突触终端会根据动作电位间歇性地释放神经递质，而视觉、听觉和前庭系统的神经元则通过调节连续释放的速率，在分级信号中编码感觉信息，并在其突触处进行传递。突触带是在这些神经元的活性区发现的一种特殊结构，对于维持连续释放所需的高胞吐速率是必要的。为了维持突触传递的保真度，胞吐作用必须通过高容量的内吞作用来平衡，以回收在囊泡融合过程中插入的多余膜。在带状神经元中囊泡释放后的电容测量表明，补偿性内吞作用有两个动力学上不同的阶段，其相对贡献随刺激强度而变化。这两个阶段可以独立调节，可能反映了在不同回收囊泡池上运行的不同潜在机制。电子显微镜显示，在网格蛋白介导的内吞作用与大量膜回收作为补偿性内吞作用机制的相对重要性方面，带状突触之间存在差异。带状突触与传统突触一样，根据特定细胞类型的生理需求，利用多种内吞途径来补充突触囊泡池。
