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J. Klooster, G. Zoidl, R. Dermietzel, M. Kamermans; Ultrastructural Localization of Pannexin1 and the ATP Receptor Subunit P2X7 in the Zebrafish Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1156.
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Pannexins are a recently discovered group of proteins capable of forming gap-junctions and hemichannels. It has been suggested that they are involved release of ATP. To determine the localization of Pannexins in the zebrafish retina, an immuno-histochemical study was performed at light (LM) and electron microscopical (EM) level using the Pannexin 1 antibody and an antibody raised against P2X7; an ATP receptor subunit.
Zebrafish retinas and brains were fixed 4% pfa and incubated with an antibody against zebrafish Pannexin1 and P2X7 ATP receptor. Standard immunofluorensence and EM techniques were performed.
At the LM level Pannexin1 immunolabeling was found in band like structures in the outer plexiform layer of the zebrafish retina. In several brain areas, including the optic tectum, punctate Pannexin1 immunoreactivity was observed. At the EM level in the zebrafish retina, some spinules show pannexin1-IR, however most labeling was concentrated in the horizontal cell dendrites just below the synaptic ribbon. Labeling was restricted to horizontal cell dendrites innervating the cone pedicle. Not all horizontal cell dendrites show Pannexin1-IR. In the zebrafish brain Pannnexin1-IR was found at one side of the neurochemical synapse. P2X7-IR was strongly present in the cone synaptic terminals.
Pannexin1 forms hemichannel in the horizontal cell dendrite in the zebrafish retina. Pannexin1-IR is not found at the location of Cx55.5 but it is located on a greater distance from the synaptic ribbon. Together with the P2X receptors in the cones, the pannexins create a feedback pathway from horizontal cells to cones. The nature and role of this feedback pathway seem to be different from the connexin hemichannel mediated feedback system.
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