Abstract
Abstract: :
Purpose: Cone dominated species are known to store retinyl esters in both neural retina and retinal pigment epithelium (RPE). However, the flow of retinoids to these two storage pools during light and dark conditions has not been studied. In the present work, cone– dominated chicken eyes were light– and dark–adapted to investigate how retinoids from cone pigments are transferred to these retinyl ester pools in the neural retina and RPE. Methods: Eyes were collected at the following time points of light/dark treatments: 2hr dark adaptation after ambient illumination, 1.5 hr exposure to bright illumination for an exhaustive bleach, an additional 1.5 hr of the same level of light exposure, 1.5 hr of dark adaptation and an additional 1.5 hr of dark adaptation. Neural retinas were carefully dissected from the RPE and then extracted with hexane for gradient HPLC. Levels of 11–cis and all–trans retinyl palmitate (cis– and trans–RP) and retinol (cis–and trans–ROH) were obtained from calibration standards. Results: Following light adaptation, the level of trans–RP in the RPE increased from 0.86 to 6.9 nmol/eye within the first 1.5 hr. However, the level of cis–RP in the RPE, as well as the cis– and trans–RP’s in the neural retina remained low (1.4 nmol/eye or less) during this initial period. From 1.5 hr to 3 hr of light adaptation, the level of trans–RP in the RPE decreased from 6.9 to 1.2 nmol/eye while the level of cis–RP in the neural retina increased to 3.5 nmol/eye. During the first 1.5 hr of dark adaptation, cis–RP in the neural retina returned to a baseline value of 1.3 nmol/eye. RPE. Relatively low levels of cis– and trans– ROH (0.96 nmol/eye or less) were recovered from neural retina and RPE. Levels of cis–ROH remained low and unchanged in both neural retina and RPE. However, there was a significant increase in the level of trans–ROH (0.04 to 0.96 nmol/eye) in the RPE during the first 1.5 hr of light adaptation. Conclusions: During light adaptation, cis–RP accumulated in the cone dominated chicken neural retina prior to dark adaptation and pigment regeneration. Upon dark adaptation, cis–RP from the neural retina is depleted, suggesting its role for pigment regeneration. The accumulation of cis–RP in cone–dominated neuroretina prior to dark adaptation may be essential for a rapid access of retinoids for cone pigment regeneration.
Keywords: retinoids/retinoid binding proteins • retina: neurochemistry • photoreceptors