TASK-1; Of all the K2P channel antibodies tested, the highest levels of immunoreactivity were observed for TASK-1 (Fig. 3). In adult retina TASK-1 immunoreactivity was restricted to the inner retina, with the highest levels of staining detected for cells located in the GCL (Fig. 3A–C). Double labelling with Brn3a and TASK-1 antibodies confirmed the expression of TASK-1 in 67.4% of RGCs (91 of 135 cells counted) with high levels of TASK-1 immunoreactivity detected on the cell bodies and also along the dendrites of labelled cells (Fig. 3D–F). Lower levels of TASK-1 staining were also observed for a subset of cells located in the INL, consistent with the location of amacrine cells (Fig. 3A). TASK-1 immunoreactivity was detected throughout postnatal development. Consistent with our qPCR data, low levels of TASK-1 immunoreactivity were observed for Brn3a positive RGCs as early as P0, with levels of TASK-1 staining increasing through postnatal development and reaching maximal levels by P14 (Supplementary Figure 4). In addition, during postnatal development TASK-1 immunoreactivity was also observed for cells located in the neuroblastic cell layer, with morphologies resembling developing horizontal cells. TASK-1 immunoreactivity was evident in these cells only between P3 and P10, was absent from these cells by P14, and was not detected in P30 adult samples (Supplementary Figure 4).