Purchase this article with an account.
A. Hatch, E.T. Villazana–Espinoza, A.T. C. Tsin; Accumulation of Retinyl Esters in a Cone–Dominated Mammalian Retina . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2035.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
A novel retinoid cycle has recently been located in the cone–dominated chicken retina. In this cone visual cycle, light causes the accumulation of 11–cis retinyl esters in the retina, which is rapidly reduced to baseline level after subsequent dark adaptation. The purpose of this study is to show that light also leads to the accumulation of retinyl esters in a cone–dominated mammalian retina.
Three experiments were carried out with four animals (13–lined ground squirrel from TLS Research; body weight: 170 gm) per experiment. In each experiment, two animals were dark–adapted overnight and two animals were light–adapted (2,000 Lux from incandescent bulbs for 1, 2, and 16 hr in each experiment). Retinoids (retinyl esters and retinols) were extracted from retinas and RPE and analyzed by HPLC.
Retinas and RPE contained only small amount of retinols. Dark–adapted retina contained 0.25 nmol (n=6) 11–cis and 0.21 nmol (n=6) all–trans retinyl ester per mg retinal protein, whereas dark–adapted RPE contained 0.19 nmol (n=4) 11–cis and 0.08 nmol (n=4) all–trans retinyl ester/mg. Light exposure for 1 and 2 hr did not significantly change the level of retinyl esters. Light exposure for 16 hr resulted in a two–fold increase in 11–cis (to 0.59 nmol/mg, n=4) and three–fold increase in all–trans retinyl ester (to 0.64 nmol/mg, n=4) in the retina and also increases in the level of 11–cis and all–trans retinyl esters in the RPE (to 0.30, n=4, and 0.24 nmol/mg, n=4, respectively).
In contrast to the chicken retina, which responds to a 20 min. light exposure with a significant increase in the level of cis retinyl ester, the ground squirrel retina did not significantly increase retinyl ester in response to a short period (1 and 2 hr) of light exposure. However, light exposure of 16 hr resulted in significant accumulation in 11–cis and all–trans retinyl esters in the retina (with an increase in both retinyl esters in the RPE also, due to low activity of the rod cycle). Our data show that upon light adaptation, ground squirrel retina accumulates both cis and trans retinyl esters rather than only cis ester found in the chicken retina. Moreover, these retinyl esters accumulated at a much slower rate, suggesting that the mammalian retina may have a higher rate of mobilization of retinyl esters (thus a lower net rate of ester accumulation). Nevertheless, our data show that the ground squirrel retina contains a cone visual cycle, as suggested by Mata et al 2002. However, this mammalian cone cycle has significantly different properties than those in the avian cone cycle. Supported by grants from the NIH and the Kronkosky Foundation.
This PDF is available to Subscribers Only