Regulation of cgmp phosphodiesterase: role of cgmp in signal transduction in the. Transduce information based on photon its absorbing. Also many membrane transporters for ionic transport. Important for its function and maintaining ion balance. Synaptic region: makes synaptic contact with nerve cells of the retina. Cation [na+ and ca2+] voltage-gated ca2+ channels open. Cytosolic ca2+ level high with steady release of transmitter. Decreased ca2+ influx and decreased release of transmitter. Less inhibitory nt that excite bipolar cells. Ligand: photon of light that changes excitation of neurons. More light = less nt released (graded) = more excitation. Rate of transmitter release from rod cells is graded to light intensity. Large range of amplification can take place. Has a light-absorbing portion of complex retinal (vit a): Absorption of light causes conformational change in retinal & cascade of events involving cgmp. This is the only light-dependent step in vision. Cgmp is an important regulatory molecule in photosensitive rod cell.