Immunolocalization of aquaporin-6 in the rat retina

Previous RT-PCR experiments revealed that the neural retina of the rat contains gene transcripts of numerous aquaporins (AQPs), including AQP6 (Tenckhoff et al., Neuroreport 16 (2005) 53-56). In the present study, we investigated the localization of AQP6 immunoreactivity in slices of the rat neural retina, and determined whether blue light injury of the retina affects the tissue distribution of this channel. AQP6 immunoreactivity was found to be selectively localized to the outer plexiform layer. Around the ribbon synapses in this layer, AQP6 labeling was co-localized with the glial water channel AQP4. AQP6 labeling was not colocalized with the marker of horizontal cells, calbindin, nor with the marker of rod bipolar cells, protein kinase Cα. Along with the degeneration of photoreceptor cells after blue light treatment of the retina, AQP6-labeled ribbon synapses disappeared, and a punctate AQP6 staining redistributed into the inner nuclear layer. The co-localization of AQP6 and the glial water channel AQP4 suggests a preferential localization of AQP6 in glial membranes that surround the ribbon synapses in the outer plexiform layer. AQP6 might be involved in the glia-mediated osmo and ion regulation of the extracellular space in this layer.