Function and regulation of the photoreceptor hyperpolarization-gated channel HCN1

All cells exhibit electrical activity and some have adapted this electrical activity to act as a biological signal. A notable example of this are neurons, which use electrical signals to rapidly relay incoming information, allowing us to see, hear, feel, and think. The electrical properties are mediated by gene products known as ion channels. Many different ion channels exist, and precise electrical signals are generated by the coordinated action of these channels, with each playing a specific role. Here we examine the photoreceptor, the light sensitive cells whose finely tuned function is the foundation of vision. Photoreceptors generate an electrical signal in response to the presence of light and this signal is formed by the action of multiple ion channels including HCN1, whose role is not fully understood. We find that HCN1 prevents photoreceptors from responding too strongly to light which would lead to excessive information being passed onto the visual pathways causing visual signaling dysfunction under bright conditions. Many cellular processes regulate ion channel function. We examined the regulation of HCN1 channels. We identified a signal required for HCN1 to be inserted into the plasma membrane where it functions. Unlike other signals of similar function, this signal appears to depend on the shape of the HCN1 channel. We also discovered a novel protein interaction that may be involved in regulating the number of HCN1 channels present which would directly impact the number of ions this channel allows into the cell altering its contribution to the electrical properties of the cell.