Quantitative PCR analysis shows widespread expression of K2P channel mRNA in the wildtype mouse retina (n = 5, P135, tissue collected at Zeitgeber time ZT8, 8 hours after light onset) (Fig. 1). The highest levels of mRNA expression were detected for TWIK-1, TASK-1, TRAAK, and TRESK, with mRNA transcripts for TWIK-2, TWIK-3, TREK-1, TREK-2, TASK-3, TASK-5 and THIK-1 detected at lower levels. mRNA encoding TASK-2, THIK-2 and TALK-1 were not detected in retina cDNA samples (as determined by a lack of measurable CT value after 40 cycles of PCR). Levels of K2P channel mRNA expression are seemingly highly dynamic in the mouse retina with developmental and circadian variation of expression detected for nearly all channels investigated (Supplementary Figure 1). For the majority of K2P channels, including TWIK-2, TREK-1, TRAAK, TASK-1, TASK-3, TASK-5, and TRESK, a clear up regulation of mRNA expression was detected throughout postnatal development with expression typically reaching maximal levels by P14. By contrast, TWIK-1 and TASK-2 were expressed at higher levels early during postnatal development (all tissue collected at ZT8) (Supplementary Figure 1A). Furthermore, numerous K2P channels were found to exhibit rhythmic patterns of mRNA expression under 12:12 light dark cycles (Supplementary Figure 1B). For the majority of channels, including TWIK-1, TWIK-2, TRAAK, TASK-1, TASK-3 and TASK-5, levels of mRNA expression were highest during the subjective night and typically lowest 8 hours after light onset (ZT8). In contrast, TREK-1 and TRESK showed opposing patterns of expression, with mRNA for these channels peaking at ZT8.