ABSTRACT
The neural retina is the complex, multicell type tissue at the back of the eye responsible for converting light stimuli into neural impulses directed to the brain. Visual pigment proteins such as rhodopsin in rod photoreceptor cells and blue, green, and red opsins in cone photoreceptor cells absorb light via photoisomerization of proteinbound 11-cis -retinal, triggering visual signal transduction, that is, phototransduction. These light-absorbing proteins are integral membrane proteins located in the outer segments of photoreceptor cells, within densely packed membranous discs containing other proteins involved in phototransduction. Additional cells in the retinal circuitry, including bipolar and ganglion cells, process and relay the signal from the photoreceptors through the nerve fi ber layer to the optic nerve, modulated in part by horizontal and amacrine cells and supported by retinal glial cells such as Müller cells,
astrocytes, and microglia. Although the neural retina also has an internal vasculature, the photoreceptor cells are separated from their principal blood supply in the choroid by the retinal pigment epithelium (RPE), a polarized single-cell layer that plays key roles in retinal physiology. Worldwide efforts continue toward a better understanding of the complex processes ongoing in retina, including regulation of visual sensitivity and dark adaptation, regeneration of 11-cis -retinal for rod and cone visual pigments (the visual cycle), and neuronal transmission.1 Proteomic approaches offer signifi - cant potential for deciphering molecular mechanisms in healthy and diseased retina. Nevertheless, such studies remain challenged by the many different and diffi cultto-purify cell types in the retina, a correspondingly complex retinal proteome, and a relatively high proportion of membrane proteins.
