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There is increasing evidence that ATP acts on purinergic receptors and mediates synaptic transmission in the retina. In a previous study, we raised the possibility that P2X-purinoceptors, presumably P2X(2)-purinoceptors in OFF-cholinergic amacrine cells, play a key role in the formation of OFF pathway-specific modulation. In this study, we examined whether the P2Y(1)-purinoceptors can function in cholinergic amacrine cells in the mouse retina since cholinergic amacrine cells in the rat retina express P2Y(1)-purinoceptors. P2Y(1)-purinoceptors were shown to be expressed in dendrites of both ON- and OFF-cholinergic amacrine cells in adults. At postnatal day 7, there was immunoreactivity for P2Y(1)-purinoceptors in the soma of cholinergic amacrine cells. At postnatal day 14, weak immunoreactivity for P2Y(1)-purinoceptors was detected in the dendrites but not in the soma of cholinergic amacrine cells. At postnatal day 21, strong immunoreactivity for P2Y(1)-purinoceptors was detected in dendrites of cholinergic amacrine cells. The expression pattern of P2Y(1)-purinoceptors was not affected by visual experience. We concluded that P2Y(1)-purinoceptors are not involved in the OFF-pathway-specific signal transmission in cholinergic amacrine cells of the mouse retina.

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Metabotropic glutamate receptor 6, mGluR6, interacts with scaffold proteins and Gβγ subunits via its intracellular C‐terminal domain (CTD). The mGluR6 pathway is critically involved in the retinal processing of visual signals. We herein investigated whether the CTD (residues 840–871) was necessary for mGluR6 cell surface localization and G‐protein coupling using mGluR6‐CTD mutants with immunocytochemistry, surface biotinylation assays, and electrophysiological approaches. We used 293T cells and primary hippocampal neurons as model systems. We examined C‐terminally truncated mGluR6 and showed that the removal of up to residue 858 did not affect surface localization or glutamate‐induced G‐protein‐mediated responses, whereas a 15‐amino acid deletion (Δ857‐871) impaired these functions. However, a 21‐amino acid deletion (Δ851‐871) restored surface localization and glutamate‐dependent responses, which were again attenuated when the entire CTD was removed. The sequence alignment of group III mGluRs showed conserved amino acids resembling an ER retention motif in the CTD. These results suggest that the intracellular CTD is required for the cell surface transportation and receptor function of mGluR6, whereas it may contain regulatory elements for intracellular trafficking and signaling.