Zanazzi George, Matthews Gary
Department of Neurobiology & Behavior, State Universtiy of New York, Stony Brook, NY 11794-5230, USA.
Mol Neurobiol. 2009 Apr;39(2):130-48. doi: 10.1007/s12035-009-8058-z. Epub 2009 Mar 3.
The primary receptor neurons of the auditory, vestibular, and visual systems encode a broad range of sensory information by modulating the tonic release of the neurotransmitter glutamate in response to graded changes in membrane potential. The output synapses of these neurons are marked by structures called synaptic ribbons, which tether a pool of releasable synaptic vesicles at the active zone where glutamate release occurs in response to calcium influx through L-type channels. Ribbons are composed primarily of the protein, RIBEYE, which is unique to ribbon synapses, but cytomatrix proteins that regulate the vesicle cycle in conventional terminals, such as Piccolo and Bassoon, also are found at ribbons. Conventional and ribbon terminals differ, however, in the size, molecular composition, and mobilization of their synaptic vesicle pools. Calcium-binding proteins and plasma membrane calcium pumps, together with endomembrane pumps and channels, play important roles in calcium handling at ribbon synapses. Taken together, emerging evidence suggests that several molecular and cellular specializations work in concert to support the sustained exocytosis of glutamate that is a hallmark of ribbon synapses. Consistent with its functional importance, abnormalities in a variety of functional aspects of the ribbon presynaptic terminal underlie several forms of auditory neuropathy and retinopathy.
听觉、前庭和视觉系统的初级受体神经元通过响应膜电位的分级变化调节神经递质谷氨酸的持续性释放，来编码广泛的感觉信息。这些神经元的输出突触以称为突触带的结构为标志，突触带将一组可释放的突触小泡系于活性区，在此处谷氨酸的释放是由通过L型通道的钙内流所引发的。突触带主要由蛋白质RIBEYE组成，RIBEYE是突触带突触所特有的，但在常规终末中调节小泡循环的细胞基质蛋白，如小突触泡蛋白和巴松管蛋白，也存在于突触带。然而，常规终末和突触带终末在其突触小泡池的大小、分子组成及动员方面存在差异。钙结合蛋白和质膜钙泵，连同内膜泵和通道，在突触带突触的钙处理中发挥重要作用。综合来看，新出现的证据表明，几种分子和细胞特化协同作用，以支持谷氨酸的持续胞吐作用，这是突触带突触的一个标志。与其功能重要性相一致，突触带突触前终末的各种功能方面的异常是几种形式的听觉神经病和视网膜病的基础。
