Cellular localization of P2Y₆ receptor in rat retina

Extracellular nucleotides exert their actions via two subfamilies of purinoceptors: P2X and P2Y. Eight mammalian P2Y receptor subtypes (P2Y(1,2,4,6,11,12,13,14)) have been identified. In this work, the localization of P2Y(6) was studied in rat retina using double immunofluorescence labeling and confocal scanning microscopy. Immunostaining for P2Y(6) was strong in the outer plexiform layer and was diffusely distributed throughout the full thickness of the inner plexiform layer. In addition, P2Y(6) immunoreactivity was clearly observed in many cells in the inner nuclear layer and the ganglion cell layer. In the outer retina photoreceptor terminals, labeled by VGluT1, and horizontal cells, labeled by calbindin, were P2Y(6)-positive. However, no P2Y(6) immunostaining was detected in bipolar cells, labeled by homeobox protein Chx10. In the inner retina P2Y(6) was localized to most of GABAergic amacrine cells, including dopaminergic and cholinergic ones, stained by tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) respectively. Some of glycinergic amacrine cells, but not glycinergic AII amacrine cells, were also labeled by P2Y(6). Moreover, P2Y(6) immunoreactivity was seen in almost all ganglion cells, labeled by Brn3a. In Müller glial cells, stained by cellular retinaldehyde binding protein (CRALBP), however, no P2Y(6) expression was found in both somata and processes. We speculate that P2Y(6) may be involved in retinal information processing in different ways, probably by regulating the release of transmitters and/or modulating the radial flow of visual signals and lateral interaction mediated by horizontal and amacrine cells.