TWIK-2; TWIK-2 immunoreactivity was consistently detected in cells of the GCL (Fig. 2G,H). Double labelling with Brn3a confirms these cells to be RGCs, with TWIK-2 immunoreactivity detected for 60.8% (73 of 120 cells counted) of all Brn3a positive RGCs in the adult retina including RGCs with multiple distinct morphologies (Fig. 2I). Typically, the highest level of TWIK-2 immunoreactivity was observed along dendrites of immunoreactive cells, with lower levels of immunoreactivity observed for cell bodies. Consistent with qPCR analysis (Supplementary Figure 1), levels of TWIK-2 expression are low during early postnatal development with TWIK-2 immunoreactivity not detected within RGCs prior to P10, and increased by P14 and P30 (Supplementary Figure 3). TWIK-3; TWIK-3 immunoreactivity was observed for 50.5% (54 of 107 cells counted) of cells within the ganglion cell layer of the adult retina (Fig. 2J–L). TWIK-3 immunoreactivity was largely restricted to the cell membrane of reactive cell bodies, with only minimal labelling detected along cellular process. However, due to species limitations it was not possible perform double labelling with this TWIK-3 antibody and the Brn3a antibody used to identify RGCs (both raised in goat).