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J. Cha, F. Pan, S. C. Massey, M.-H. Chun, I.-B. Kim; An Electron Microscopic Study of Connexin 50 and 57 in the Rabbit Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3047. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
There are two types of horizontal cell (HC) in the rabbit retina and they make three different coupled network: axonless A-type HC network via connexin (Cx) 50 (O’Brien et al., J Neurosci. 2006; 26:11624-36), axon-bearing B-type HC dendritic network via an unknown Cx, and B-type axon terminal network via Cx57 (Pan et al., ARVO Abst. 2007; Program # 2848). Both Cxs in each HC network appeared to be localized on the dendrites but not at the tip of dendrites, while a recent report has suggested that Cx57 may be localized at the tip of HC dendrites in the mouse retina (Ciolofan et al., Neuroscience 2007;473-88). Therefore, we wanted to determine the localization of Cx50 and 57 in the horizontal cells in the rabbit retina at electron microscopic level.
For preembedding immuno-electron microscopy, rabbit retinas were dissected and fixed in 4% paraformaldehyde and 0.5% glutaraldehyde. The tissues were then labeled with antibodies against Cx50 or Cx57. After postfixation, the tissues were embedded in Epon. Ultrathin sections were made and examined by electron microscope.
In vertical ultrathin sections of the rabbit retina, both Cx50 and 57 were identified in the outer plexiform layer (OPL) by the electron-dense reaction product. Both Cx50 and 57 were localized on HC processes, but not found on HC tip in photoreceptor synaptic terminals. The shape and size between both Cxs are quite different. Cx50 was characterized by exclusively huge (> 2 µm) in size and flat in shape, while Cx57 was smaller and wavy; more than half of them examined appeared to be invaginated or endocytosed, and the remains were flat or interdigited.
These results demonstrate that Cx50 and 57 are localized in the processes of A-type HCs and B-type HC axons but not at the tip of HC in photoreceptor synaptic terminals. These results may provide the insights into the function of gap junctions in the horizontal cell.
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