O'Brien Jennifer J, Li Wei, Pan Feng, Keung Joyce, O'Brien John, Massey Stephen C
Department of Ophthalmology and Visual Science, University of Texas Medical School at Houston, Houston, Texas 77030, USA.
J Neurosci. 2006 Nov 8;26(45):11624-36. doi: 10.1523/JNEUROSCI.2296-06.2006.
There are many examples of neuronal coupling via gap junctions in the retina. Of these, perhaps the best known is the extensive coupling between horizontal cells. In the rabbit retina, there are two types of horizontal cells, A-type and B-type, both of which are independently coupled. Connexin 50 (Cx50) cDNA, encoding a 440 aa protein, was successfully isolated from rabbit retina RNA. Cx50 was also obtained from isolated A-type horizontal cells (A-type HCs) by single-cell RT-PCR. A-type HCs were visualized by intracellular dye injection or with an antibody against calbindin. Confocal analysis revealed all Cx50 labeling occurred on the A-type HC matrix, typically at dendritic intersections. The Cx50 plaques varied in size, from punctate signals in which fine dendrites cofasciculated, to giant plaques, >50 microm(2), in which large dendrites crossed. The numerous Cx50 plaques between A-type HCs may adequately account for the remarkable coupling observed in this network. We could not detect Cx50 staining on the tips of horizontal cell dendrites within the cone pedicle invagination. This distribution does not support a role for Cx50 in hemichannel-mediated feedback. In addition, the absence of Cx50 in B-type HCs suggests the presence of a different connexin for this cell type. In summary, these results suggest that gap junctions in the A-type horizontal cell matrix are composed from Cx50. Multiple neuronal connexins are expressed in the mammalian retina and different cell types express specific connexins.
视网膜中存在许多通过缝隙连接实现神经元耦合的例子。其中，或许最为人熟知的是水平细胞之间广泛的耦合。在兔视网膜中，有两种类型的水平细胞，即 A 型和 B 型，它们均可独立耦合。从兔视网膜 RNA 中成功分离出编码 440 个氨基酸蛋白质的连接蛋白 50（Cx50）cDNA。通过单细胞逆转录聚合酶链反应（RT-PCR）也从分离出的 A 型水平细胞（A 型 HC）中获得了 Cx50。通过细胞内染料注射或使用抗钙结合蛋白抗体对 A 型 HC 进行可视化观察。共聚焦分析显示，所有 Cx50 标记均出现在 A 型 HC 基质上，通常位于树突交叉处。Cx50 斑块大小各异，从细树突共束形成的点状信号，到树突交叉的大于 50 平方微米的巨大斑块。A 型 HC 之间众多的 Cx50 斑块或许足以解释在该网络中观察到的显著耦合现象。我们在视锥小足凹陷内的水平细胞树突尖端未检测到 Cx50 染色。这种分布不支持 Cx50 在半通道介导的反馈中发挥作用。此外，B 型 HC 中不存在 Cx50 表明该细胞类型存在不同的连接蛋白。总之，这些结果表明 A 型水平细胞基质中的缝隙连接由 Cx50 组成。多种神经元连接蛋白在哺乳动物视网膜中表达，不同细胞类型表达特定的连接蛋白。
