What is the primary function of phosphodiesterase 6 (PDE6) in phototransduction?

Phosphodiesterase 6 (PDE6) plays a crucial role in the phototransduction pathway, which is the process by which light signals are converted into electrical signals in the photoreceptor cells of the retina. The primary function of PDE6 is to hydrolyze cGMP (cyclic guanosine monophosphate), thereby decreasing its levels within the photoreceptor cells.

During phototransduction, when photons of light are absorbed by rhodopsin, it triggers a cascade of biochemical events that ultimately leads to the activation of transducin, a G-protein. Activated transducin then stimulates PDE6. As PDE6 hydrolyzes cGMP, the concentration of cGMP falls. This reduction in cGMP is critical because cGMP is essential for keeping ion channels in the photoreceptor cell membrane open. When cGMP levels drop, these ion channels close, leading to hyperpolarization of the cell, which is the signal that eventually gets transmitted to the brain as a visual signal.

Therefore, the key function of PDE6 in this process is to decrease cGMP levels, which facilitates the transition from the dark state of the photoreceptors to the light-adapted