First published online October 21, 2005
Journal of Experimental Biology 208, 4151-4157 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01881
Retinoid cycles in the cone-dominated chicken retina
Simon G. Trevino,
Elia T. Villazana-Espinoza,
Albert Muniz and
Andrew T. C. Tsin*
Department of Biology, the University of Texas at San Antonio, San
Antonio, TX 78249, USA
View larger version (28K):
[in a new window]
|
Fig. 1. Accumulation of retinyl esters in the retina and retinal pigment epithelium
(RPE) of adult chicken eye. Chicken were decapitated and the heads were
transported in the dark (2 h) to the laboratory. Eye lids were removed and
eyes were light adapted (2000 lux) for two hours prior to dissection. Retina
was dissected free from RPE, and eye tissues were homogenized in Tris-HCl (pH
7.5) and extracted for retinoids by ethanol and hexane. (A) HPLC analysis of
retinoids extracted from one retina of 2 h dark-adapted (top) or one retina of
2 h light-adapted (bottom) chicken eyes. Absorbance was monitored at 318 nm in
optical density units. Peak I is 11-cis retinyl ester, with a
retention time of 5.8 min and a UV spectrum with an absorption maximum at 318
nm (inset). (B) HPLC analysis of retinoids extracted from two RPE of 2 h
dark-adapted (top) or two RPE of 2 h light-adapted (bottom) chicken eyes.
Absorbance was monitored at 325 nm in optical density units. Peak II is
all-trans retinyl ester, with a retention time of 6.5 min and a UV
spectrum with an absorption maximum at 325 nm (inset). Accumulation of
11-cis (open circles) and all-trans (filled circles) retinyl
ester in the (C) retina or (D) RPE as a function of time in response to light
(open bar) and dark (shaded bar) adaptation. Means ± S.E.M.
were calculated from results of four experiments. For each of the four
experiments, retinoid extracts from individual retina or RPE were analyzed by
HPLC and results from two retinae or two RPE (per time point) were averaged
(N=2).
|
|
View larger version (22K):
[in a new window]
|
Fig. 2. Changes in retinoids in response to light or dark adaptation in the
isolated retina. Adult chicken eyes were dark adapted for 4 h, and retinae
were dissected free of the retinal pigment epithelium (RPE) prior to exposure
to light (2500 lux) for 0.5 h, and for 1 h in vitro. Retinoids were
extracted and analyzed by HPLC. Means ± S.E.M.. were
calculated from results of two experiments. For each of the two experiments,
retinoid extracts from pooled retinae from 4-6 eyes per treatment group were
analyzed by HPLC.
|
|
View larger version (24K):
[in a new window]
|
Fig. 3. Retinoid cycles during light and dark adaptation in young chickens. Chicken
were dark adapted overnight before subjected to light exposure (2000 lux for
duration indicated in the figure). Retina was dissected free of the retinal
pigment epithelium (RPE), and retinoids were extracted (see Materials and
methods) and then analyzed by HPLC. (A) 11-cis retinal (broken line)
and 11-cis retinyl ester (solid line) pools during light (open bar)
and dark (shaded bar) adaptation (note different scales for retinal and
retinyl ester on y1- and y2-axes). (B)
All-trans retinal (broken line) and all-trans retinyl ester
(solid line) pools during light (open bar) and dark (shaded bar) adaptation.
Means ± S.E.M.. were calculated from the results of three
experiments. For each of the three experiments, retinoid extracts from
individual retina or RPE were analyzed by HPLC and results from two retinae or
two RPE (per time point) were averaged (N=2).
|
|
View larger version (20K):
[in a new window]
|
Fig. 4. Hypothetical cone cycle in the retina and rod cycle in the retina/retinal
pigment epithelium (RPE) of the chicken eye. Chicken retina stores
11-cis retinyl esters and chicken RPE stores all-trans
retinyl esters. Light bleaches photopigments in the retina, leading to the
accumulation of 11-cis retinyl esters in the retina and
all-trans retinyl ester in the RPE. In the dark, 11-cis and
all-trans retinyl ester pools deplete while visual pigments
regenerate. The amount and the rates of accumulation/depletion of
11-cis retinyl esters in the retina correspond to the bleaching and
regeneration of cone pigments, providing support for a cone visual cycle in
the chicken retina. The amount and the rates of accumulation/depletion of
all-trans retinyl esters in the RPE correspond to the bleaching and
regeneration of rod pigments, thus supporting a rod visual cycle in the
chicken RPE/retina. The types of retinal cell where 11-cis retinoids
are synthesized and stored, as well as the biochemical mechanism of
isomerization, are not known. The method to partition these two visual cycles
remains to be studied.
|
|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati 
Twitter What's this?
© The Company of Biologists Ltd 2005
