HCN1 channels significantly shape retinal photoresponses.

In this chapter, the impact of HCN1 channels on the retinal functional properties was presented. HCN1 channel loss led to an intensity-dependent prolongation of the rod system response, in agreement with the threshold mechanism of activation of the channel. Rod outer segment functionality was not altered, supporting the main site of action in the inner segment. Fixed-intensity variable frequency flicker series showed a regular amplitude decline near threshold and a reduced flicker fusion frequency above threshold due to increased waveform width. It was suggested that shortening and shaping of light responses by activation of HCN1 is an important step at least in the scotopic pathways. The retina of HCN1 knockout animals provides a valuable system with which to study the role of HCN1 in the shaping and processing of retinal light responses especially to repetitive stimulation.