Figure 3.

Rhodopsin (R) is concentrated in the disc membranes of rod photoreceptor cells. Rhodopsin contains the chromophore 11-cis retinal, which under light stimulation is converted in all-trans retinal. The photoactivated Rhodopsin (R*) triggers a signal transduction cascade, leading to activation of the phosphodiesterase (PDE) and a consequent decrease in cGMP and closure of the Na⁺ dark current. While retinoid pathway follows the renewal of 11-cis retinal at the retinal pigment epithelium (RPE).