Mammalian photoreceptors use sunlight to rapidly regenerate visual pigments

FINDINGSMammals see when light reflected from an object strikes a visual pigment in the eye, which sends a signal to the brain and simultaneously consumes the light-sensitive pigment in retinal photoreceptor cells. In theory, this could present a problem because mammals cannot see if the light-sensitive pigments are depleted. But now UCLA researchers have learned why that never happens. They observed that in bright light mammals rapidly recycle spent pigments, ensuring that photoreceptors retain levels of light-sensitive pigments sufficient for uninterrupted sight.  BACKGROUNDWhen stimulated, the light-sensitive pigment in the retina — called 11-cis retinal — oxidizes to a light-insensitive form called all-trans. Nobel Prize-winning work conducted 50 years ago demonstrated that mammals use an enzyme pathway called the visual cycle to convert all-trans back to light-sensitive 11-cis retinal. When scientists learned that mu lti-step enzymatic reactions like this often work slowly, it presented a mystery. How could the classic pathway replenish the 11-cis retinal fast enough in bright light, which oxidizes the light-sensitive pigment more quickly than dim light conditions?UCLA researchers found that when stimulated by blue light, a phospholipid residing in rod and cone membranes, called  N-ret-PE, undergoes conversion to 11-cis retinal without enzymes.METHODThe team performed a biochemical analysis using cow and mouse retinas. First, the researchers verified that light...
Source: UCLA Newsroom: Health Sciences - Category: Universities & Medical Training Source Type: news