Fig. 4.
S1P receptors are expressed by amacrine cells. A: S1P1R is thought to couple to Gi exclusively, whereas S1P3R can couple to Gi, Gq, or G13. Signaling through these G proteins converges at the level of PLC activation. B: Western blot analysis of the S1P1R antibody reveals a single band present for both chicken and rat brain homogenates just below the 50-kDa marker, consistent with the predicted molecular weight for the S1P1R (47 kDa). C: secondary-only controls did not show any nonspecific labeling in cultured cells. D: the S1P1R antibody labels all amacrine cell bodies (arrows) and their processes in culture. Cone photoreceptors label intensely with this antibody (asterisks) and have been overexposed in this image so that the amacrine cell labeling can be observed. E: in a pattern similar to the S1P1R antibody, the S1P3R antibody labels all amacrine cell bodies and their processes in cell culture. All of the cells in this image are amacrine cells. Scale bars are 25 μm. F: S1P3R gene-specific primers were use to amplify mRNA from ∼15 amacrine cells collected from a culture dish. The PCR product produced a single band of the appropriate size (156 bp). The identity of the product as a component of the transcript encoding S1P3R was confirmed by sequence analysis.