R is localized specifically to a morphologically distinct part of the cell, the outer segment.
Cation channels are directly gated by cGMP and control the influx of ions across photoreceptor plasma membranes. The hydrolysis of cGMP by PDE results in a change in cGMP-gated channel conformation, resulting in channel closure. Channel closure decreases the conductance of the plasma membrane to cations, and results in the hyperpolarization of the plasma membrane, inhibition of neurotransmitter release, and signaling of the light stimulus to adjacent neurons. Reprinted from Trends in Neurosciences, vol.