Department of Ophthalmology, School of Medicine, New York University, 550 First Avenue, MSB 149, New York, NY 10016, USA.
Prog Retin Eye Res. 2013 May;34:1-18. doi: 10.1016/j.preteyeres.2012.12.002. Epub 2013 Jan 8.
Gap junctions connect cells in the bodies of all multicellular organisms, forming either homologous or heterologous (i.e. established between identical or different cell types, respectively) cell-to-cell contacts by utilizing identical (homotypic) or different (heterotypic) connexin protein subunits. Gap junctions in the nervous system serve electrical signaling between neurons, thus they are also called electrical synapses. Such electrical synapses are particularly abundant in the vertebrate retina where they are specialized to form links between neurons as well as glial cells. In this article, we summarize recent findings on retinal cell-to-cell coupling in different vertebrates and identify general features in the light of the evergrowing body of data. In particular, we describe and discuss tracer coupling patterns, connexin proteins, junctional conductances and modulatory processes. This multispecies comparison serves to point out that most features are remarkably conserved across the vertebrate classes, including (i) the cell types connected via electrical synapses; (ii) the connexin makeup and the conductance of each cell-to-cell contact; (iii) the probable function of each gap junction in retinal circuitry; (iv) the fact that gap junctions underlie both electrical and/or tracer coupling between glial cells. These pan-vertebrate features thus demonstrate that retinal gap junctions have changed little during the over 500 million years of vertebrate evolution. Therefore, the fundamental architecture of electrically coupled retinal circuits seems as old as the retina itself, indicating that gap junctions deeply incorporated in retinal wiring from the very beginning of the eye formation of vertebrates. In addition to hard wiring provided by fast synaptic transmitter-releasing neurons and soft wiring contributed by peptidergic, aminergic and purinergic systems, electrical coupling may serve as the 'skeleton' of lateral processing, enabling important functions such as signal averaging and synchronization.
缝隙连接将所有多细胞生物的细胞连接在一起，通过利用相同（同源）或不同（异源）的连接蛋白亚基形成同源或异源（即分别在相同或不同的细胞类型之间建立）的细胞间接触。神经系统中的缝隙连接在神经元之间传递电信号，因此也被称为电突触。这种电突触在脊椎动物的视网膜中特别丰富，它们专门用于在神经元和神经胶质细胞之间形成连接。在本文中，我们总结了不同脊椎动物视网膜细胞间偶联的最新发现，并根据不断增加的数据，确定了一般特征。特别是，我们描述和讨论了示踪剂偶联模式、连接蛋白、连接电导和调节过程。这种多物种比较指出，大多数特征在脊椎动物类群中都非常保守，包括（i）通过电突触连接的细胞类型；（ii）连接蛋白组成和每个细胞间接触的电导；（iii）每个缝隙连接在视网膜回路中的可能功能；（iv）缝隙连接是神经胶质细胞之间电偶联和/或示踪剂偶联的基础。这些泛脊椎动物的特征表明，在脊椎动物 5 亿多年的进化过程中，视网膜缝隙连接几乎没有变化。因此，电偶联的视网膜回路的基本结构似乎和视网膜本身一样古老，这表明缝隙连接从脊椎动物眼睛形成的一开始就深深地融入了视网膜的布线中。除了由快速突触递质释放神经元提供的硬连线和由肽能、胺能和嘌呤能系统贡献的软连线之外，电偶联可能作为侧部处理的“骨架”，从而实现信号平均和同步等重要功能。
