Outer Segments Of Visual Cells Research Articles

Bionics study on the MFD of human visual cells

Human visual cells are photon detectors and its outer segment is similar to optical fibers, so based on waveguide theory, in this research, the normalized frequency and mode field diameter (MFD) of human visual cell's outer segment were calculated and analyzed. For cone cells, wavelength data was sampled at 380nm, 419nm, 531nm, 559nm and 760nm; for rod cells wavelength data was sampled at 380nm, 498nm and 760nm. It was shown that the outer segment of cone cells works in single mode; for rod cells, its outer segment works as multimode. This analysis is referential to the bionics design of photoelectric converters which will meet the high requirement of optical communication in the near future.

Fatty acid compositions of arthropod and cephalopod photoreceptors: interspecific, seasonal and developmental studies

Fatty acid compositions of the compound eyes of insects (soldier-bug, Hemiptera, and silk moth, Lepidoptera), crustaceans (crayfish and grapsid crab, Decapoda) and inner and outer segments of visual cells of a squid (Cephalopoda, Mollusca) were analyzed by gaschromatography for interspecific comparison. Fatty acid compositions showed great variation among species. In insect compound eyes, 16:0 and 18:0 were the main saturated fatty acids, and 18:1 was the dominant unsaturated fatty acid. Silk moth eyes contained, in addition, considerable amounts of 18:2 and 20:5. In crustacean compound eyes, the main saturated fatty acids were 16:0 and 18:0, and 14:0 (5.0%) was only detected in grapsid crabs; the main unsaturated fatty acids were 20:4, 20:5 and 22:6. Both whole eyes and rhabdom fraction of crayfish showed similar profiles of fatty acid compositions. Both inner and outer segments of squid retinae were characterized by high amounts of unsaturated fatty acids, especially 22:6. Compound eyes of grapsid crabs were used for the experiments on seasonal changes of fatty acid compositions. UFA/SFA ratios (weight in % of unsaturated fatty acids saturated fatty acids) were lowest (1.0) in July and highest (2.5) in March, and unsaturation indexes (average number of double bonds per molecule) were lowest (1.5) in July and highest (2.3) in March. Fatty acids 18:0 and 20:1 showed a significant correlation with the changes of seasonal temperature. Fatty acid analysis of the developing compound eyes of silk moths during the pupal stage revealed that eicosapentanoic acid (20:5) increased remarkably in parallel with the development of photoreceptive membranes, the rhabdoms. This suggests that eicosapentaenoic acid may play an important role in formation and function of rhabdoms.

Chronic clorgyline dampens rat retinal rhythms

In the rat retina, the rhythm of disk-shedding from visual cell outer segments is circadian in nature, whereas autophagic degradation of organelles in inner segments follows a circadian rhythm that persist in constant light but not in constant darkness. The monoamineoxidase inhibitor clorgyline can phase delay circadian rhythms in hamster and rat. However, clorgyline does not phase delay the plasma corticosterone rhythm nor does it delay the phase position of the retinal disk-shedding rhythm in a light-dark cycle or in constant darkness: only the amplitude of the circadian rhythm is reduced. A marked reduction in rhythm amplitude is also found in the number of autophagic vacuoles after chronic clorgyline treatment. Thus the circadian rhythm of disk-shedding appears to be primarily driven by an oscillator within the eye, and clorgyline modulates the light response of retinal parameters but not their timing.

108] Cephalopod retinochrome

Publisher Summary This chapter discusses the cephalopod retinochrome. The cephalopod retina has a dual system of photosensitive chromoproteins with retinaldehyde as chromophores rhodopsin and retino-chrome. Rhodopsin is associated only with microvillar membranes of the outer segments of visual cells, whereas retinochrome is found in both inner and outer segments. The two photopigments differ from each other in the stereoisomeric form of their chromophore retinal, which is 11- cis in rhodopsin but all- trans in retinochrome. Retinochrome can be extracted also from the released fragments of outer segments. In the squid Loligo pealei , it is contained equally in both the inner and outer segments, and in Todarodes pacificus, much more is found in the outer segments. As retinochrome in the outer segments increases markedly during light adaptation of animal, it seems likely that some retinochrome protein moves forward from the inner to the outer segments and reacts there with metarhodopsin.

Recovery of the rabbit retina after light damage (preliminary observations)

The retinae of anaesthetised Dutch rabbits were exposed to one of two intensities of white light for a period of 1 h. After exposure the animals were allowed to recover for various periods up to 4 weeks. The animals were then killed, and retinal and choroidal tissue was taken for investigation by both light and electron microscopy. Exposure to the lower intensity produced disruption of the visual cell outer segments and distension of the pigment epithelium. Recovery from this insult was rapid although disturbances in rod disc stacking and a loss of cone cell outer segments were evident 4 weeks after exposure. Exposure to the higher intensity resulted in necrosis of visual cells and pigment epithelial cells. Non-native phagocytic cells were active in the removal of cellular debris. Recovery from this insult was not observed. Four weeks after exposure much of the previously illuminated retina was reduced to disorganised Müller cells and occasional macrophages.

Light damage to the retina

The retinae of anaesthetised Dutch rabbits were exposed to light of various known intensities for a period of 1 h. After this period the animals were sacrificed and tissue taken for investigation by light and electron microscopy. Changes were apparent in the visual cells and retinal pigment epithelium only at the highest intensities employed. The retinal pigment epithelium and the outer nuclear layer exhibited mild oedematous changes. The major components to be affected were the visual cell outer segments. Marked disruption and vesiculation were features of the cone outer segments, which was in distinct contrast to the focal damage observed in the rod outer segments.

Retinal lipidosis in albino rats treated with chlorphentermine and with tricyclic antidepressants

Retinal pigment epithelium is known to be engaged in continuous phagocytosis and digestion of old discs of visual cell outer segments, which have a high phospholipid content. The present ultrastructural study was focused mainly on the effects, upon pigment epithelium, of several drugs that are thought to interfere with the enzymatic degradation of phospholipids. Albino rats received high oral doses of chlorphentermine, iprindole, 1-chloroamitriptyline, imipramine, or clomipramine. After treatment for several weeks the pigment epithelial cells were doubled in height due to deposition of excessive amounts of abnormal cytoplasmic inclusions which had a crystalloid substructure. Such inclusions which are known from previous studies to be associated with drug-induced phospholipid storage are suggested to contain nondigestible phospholipids, which in pigment epithelium originate mainly from phagocytosed outer segment discs. The alterations were reversible by withdrawal of the drugs. The functional implications of the epithelial alterations remain to be elucidated. Additional examination of the neuroretina revealed numerous abnormal inclusions, mainly of multilamellated structure. Ganglion cells were affected most. The neuroretinal alterations were reminiscent of those described in human cases of inherited lipidoses.

Precision of sodium dodecyl sulfate-polyacrylamide-gel electrophoresis for the molecular weight estimation of a membrane glycoprotein: Studies on bovine rhodopsin

Criteria for assessing the precision and accuracy of methods for estimation of molecular weight for proteins using sodium dodecyl sulfate-polyacrylamide-gel electrophoresis have been applied to rhodopsin from bovine visual cell outer segment membranes. Various methods of preparing this hydrophobic protein for electrophoresis differ in their ability to solubilize and disaggregate polypeptide constituents of the outer segment membrane, with resultant variations in the pattern of protein bands and the apparent molecular weight of rhodopsin. Even with optimal solubilization and disaggregation, the behavior of rhodopsin relative to a series of standard proteins is such that the apparent molecular weight decreases systematically from 40,400 to 34,500 as the acrylamide concentration increases from 4 to 10%. As demonstrated by Ferguson plots of log R f vs gel concentration and split gel experiments, this discrepancy is explained by the fact that the extrapolated R f for zero gel concentration ( Y 0) for rhodopsin is significantly lower than the Y 0's for the soluble proteins used as molecular weight standards. In such cases, a possibly more reliable molecular weight estimate is obtained by plotting the retardation coefficient ( K R ) vs molecular weight. This method yields a value of 29,500 ± 1000 for bovine rhodopsin if only the errors in measurement of R f are considered and a quadratic relationship between K R and molecular weight is used. Using weighted linear regression for K R vs molecular weight, we obtain a molecular weight estimate of 32,700 ± 5000 when the uncertainty in the calibration curve is considered. Because of uncertainties regarding the detergent-binding properties of rhodopsin and the relationship of its Stokes radius to its molecular weight by comparison with the soluble protein standards, these values must be viewed with caution.

Postembryonic eye degeneration in the troglobitic salamander Typhlotriton spelaeus.

Comparative histological observations of the eyes of Typhlotriton spelaeus and several epigean, plethodontid species indicate that the principal postembryonic degenerative changes in the eyes of T. spelaeus involve the eyelids and cornea, visual cells, outer plexiform layer, and the pigment epithelium. Ordinarily these changes were initiated after metamorphosis, before attainment of sexual maturity, but a few larvae had degenerating retinae. The corneal epithelium becomes irregular and thin as eyelids develop during and after metamorphosis, but retains its larval structure in animals in which eyelid overlap is incomplete. Disruption and vacuolation of the lens sometimes occurs in postmetamorphic animals with degenerating visual cells. Retinal degeneration involves reduction of the inner and outer segments of visual cells, loss of the outer plexiform layer, and retraction of apical processes of the pigment epithelium. In its earliest stage, retinal reduction is first apparent at the retinal margin where visual cells are normally less well-differentiated, but in its terminal stage reduction has gone to completion over the entire retina. Extent of retinal degeneration in adults is directly related to postmetamorphic age but there is variability in each age group. Females generally have smaller eyes, and more extensive degeneration of visual cells than males. The loss of visual function in adults is correlated with extensive visual cell degeneration.

Renewal of glycerol in the visual cells and pigment epithelium of the frog retina.

The renewal of glycerol in the visual cells and pigment epithelium of the frog retina was studied by autoradiographic analysis of animals injected with [2-(3)H]glycerol. Assay of chloroform:methanol extracts showed that the labeled precursor was used mainly in lipid synthesis, although there was also some utilization in the formation of protein. Radioactive glycerol was initially concentrated in the myoid portion of rods and cones, indicating that this is the site of phospholipid synthesis in visual cells. The glycogen bodies (paraboloids) of accessory cones were also heavily labeled, suggesting the diversion of some glycerol into glycogenic pathways. In the pigment epithelium, only the oil droplets became significantly radioactive. The outer plexiform layer (which contains the visual cell synaptic bodies) and the cone oil droplets gradually accumulated considerable amounts of labeled material. Within 1-4 h, labeled molecules began to appear in the visual cell outer segments, evidently having been transported there from the myoid portion of the inner segment. Most of these were phospholipid molecules which became distributed throughout the outer segments, presumably replacing comparable constituents in existing membranes. In rods only, there was also an aggregation of labeled material at the base of the outer segment due to membrane biogenesis. These highly radioactive membranes, containing labeled molecules of lipid and protein, were subsequently displaced along the rod outer segments due to repeated membrane assembly at the base. The distribution of radioactivity supported the conclusion that membrane renewal by molecular replacement is more rapid for lipid than it is for protein.

Renewal of fatty acids in the membranes of visual cell outer segments.

The renewal of fatty acids in the visual cells and pigment epithelium of the frog retina was studied by autoradiographic analysis of animals injected with tritiated palmitic, stearic, or arachidonic acids. Most of the radioactive material could be extracted from the retina with chloroform-methanol, indicating that the fatty acids had been esterified in lipids. Analysis of the extracts, after injection of [(3)H]palmitic acid, revealed that the radioactivity was predominantly in phospholipid. Palmitic acid was initially concentrated in the pigment epithelium, particularly in oil droplets which are storage sites for vitamin A esterified with fatty acid. The cytoplasm, but not the nucleus of these cells, was also heavily labeled. Radioactive fatty acid was bound immediately to the visual cell outer segment membranes, including detached rod membranes which had been phagocytized by the pigment epithelium. This is believed to be due to fatty acid exchange in phospholipid molecules already situated in the membranes. Gradually, the concentration of radioactive material in the visual cell outer segment membranes increased, apparently as a result of the addition of new phospholipid molecules, possibly augmented by the transfer from the pigment epithelium of esterified vitamin A. Injected fatty acid became particularly concentrated in new membranes which are continually assembled at the base of rod outer segments. This localized concentration was short-lived, apparently due to the rapid renewal of fatty acid. The results support the conclusion that rods renew the lipids of their outer segments by membrane replacement, whereas both rods and cones renew the membrane lipids by molecular replacement, including fatty acid exchange and replacement of phospholipid molecules in existing membranes.

Biogenesis and renewal of visual cell outer segment membranes

Visual cell outer segment membranes are formed by the growth of existing membrane. Membrane components are synthesized at one or more sites outside the membrane system, and are then transported to it for membrane assembly. Protein and carbohydrate are produced in the myoid portion of the visual cell inner segment, and are delivered to the outer segment by way of the connecting cilium. The same may be true of phospholipid, but this is currently less certain, and the possibility of multiple synthetic sites has not been excluded. The pigment epithelium appears to play a significant role in lipid metabolism of outer segment membranes. Whether membrane constituents are combined prior to insertion in the growing membrane, or remain separate until the stage of membrane assembly is not known. There are two mechanisms by which outer segment membranes are renewed. Renewal by membrane replacement takes place only in rods, and involves assembly of new membrane at the base of the outer segment, coupled with shedding of old membrane from the apex of that structure. Renewal by molecular replacement occurs in both classes of visual cells. The rate of membrane renewal by molecular replacement differs between rods and cones and varies depending upon the molecule.

Visual pigments of men, moles and hedgehogs

Visual pigments were extracted from the dark-adapted retinas of humans, moles and hedgehogs. The λ max of the hedgehog rhodopsin is at 499 nm, while that of the mole is close to the human, at 493–494 nm. The yield of pigment from the mole eye, when considered in conjunction with histological data published previously, indicates that the axial absorbance per photoreceptor is 0.096. This suggests that the width of the spectral sensitivity curve of the mole eye, as well as the λ max, is similar to that of the human scotopic function. The absorbance per μm is 0.03 in the mole visual cell outer segment, about twice that in other species, but it is possible that some of the extracted pigment may have originated from outer segment particles phagocytosed by the pigment epithelium, so leading to a spuriously high estimate for the axial absorbance of the visual cells. It is concluded that the concentration of rhodopsin in mole photoreceptors is probably not abnormally high. The λ max of mole, hedgehog and human pigments lies within the range of λ max found in other terrestrial animals.

A study of the ultrastructure of visual cell outer segment membranes

Aldehyde-fixed chick retina was embedded in a water-containing resin of glutaraldehyde and urea without dehydration. The loss of lipids and other soluble tissue components thereby was minimized and protein denaturation caused by osmium tetroxide postifixation was avoided. Ultrathin sections were stained with (a) uranyl acetate and lead citrate, (b) silicotungstic acid, or (c) osmium vapor prior to electron microscope examination of visual cell outer segment ultra-structure at magnifications up to 800 000 diameters. The two membranes forming an outer segment disc are closely apposed, yielding a total disc thickness of about 230 Å. Interdiscal cytoplasm appears to be retained, and the staining reactions suggest that the membranes are preserved with less alteration in structure than is caused by conventional techniques. A thin layer containing mucopolysaccharide separates the two disc membranes. In cones, this layer is continuous with the intercellular mucopolysaccharide substance.

A Study of the Ultrastructure of Visual Cell Outer Segment Membranes, Using a Water-Miscible Embedding Medium and Differential Staining

Aldehyde-fixed chick retina was embedded in a water-containing resin of glutaraldehyde and urea, without dehydration. The loss of lipids and other soluble tissue components, which is severe in routine methods involving dehydration, was thereby minimized. Osmium tetroxide post-fixation was not used, lessening the amount of protein denaturation which occurred. Ultrathin sections were stained with 1, uranyl acetate and lead citrate, 2, silicotungstic acid, or 3, osmium vapor, prior to electron microscope examination of visual cell outer segment ultrastructure, at magnifications up to 800,000.Sections stained with uranyl acetate and lead citrate (Fig. 1) showed that the individual disc membranes consisted of a central lipid core about 78Å thick in which dark-staining 40Å masses appeared to be embedded from either side.

X-ray diffraction from outer segments of visual cells in intact eyes of the frog.

X-RAY diffraction patterns have been obtained from the light receptor membranes of frog retinal rod outer segments (of Rana temporaria and pipiens)1,2 and a one dimensional electron density profile across the membrane has been derived1. Until now the closest approach to studying the membranes in physiological conditions has been to pass X-rays through the outer segment layer of a strip of retina dissected from an eye and placed in a chilled glucose-supplemented Ringer solution1. To obtain a higher resolution electron density profile and minimize the possibility of artefact production, I have recorded X-ray diffraction patterns from photoreceptor layers in intact isolated whole eyes and also from eyes in a pithed frog with its heart beating throughout the experiment. Insofar as the respiratory system keeps functioning and the choroid and retina adjacent to the outer segments are intact, this experiment approaches an in vivo study.

THE ROLE OF THE PIGMENT EPITHELIUM IN THE ETIOLOGY OF INHERITED RETINAL DYSTROPHY IN THE RAT

Visual cell outer segment renewal was studied in eyes of mutant Royal College of Surgeons (RCS) and Sprague-Dawley (control) rats by a combination of microscopy and radioautography with the light and electron microscopes. RCS and control rats were injected with amino acids-(3)H at 11 days of age. Radioactive rod outer segment discs were assembled at the outer segment base from radioactive proteins synthesized in the rod inner segments. In controls, all radioactive discs assembled at 11 days of age were displaced the length of the outer segments, removed from outer segment tips, and phagocytized by the pigment epithelium by 8 days after injection. In the RCS rats, disc assembly and displacement resembled controls for the first 3 days after injection. However, as disc assembly continued for some time thereafter, a layer of labeled, disorganized, lamellar debris accumulated between the outer segment tips and the pigment epithelium. The buildup of debris was accompanied by visual cell death. At no time during the study was there evidence for phagocytic activity by the pigment epithelium. 61 days after injection, the layer of debris was the only heavily radioactive component in the retina. In the retina of RCS rats, the outer segment renewal mechanism malfunctions because the pigment epithelium does not fulfill its normal phagocytic role. The end result is visual cell death and blindness.

Properties of Rhodopsin Dependent on Associated Phospholipid

Abstract Rhodopsin prepared from frozen bovine retinal tissue by washing the visual cell outer segment fraction with Tergitol XH and solubilizing in Triton X-100 contains approximately 91 µmoles of phospholipid per µmole of rhodopsin and shows spectral ratios (A278:A498 = 1.85;A400:A498 = 0.183) approaching those of the best preparations obtainable by chromatographic procedures. Removal of most of the phospholipid associated with the protein results in a decrease in the molar extinction coefficient at 498 mµ, an increase in the reactivity of sulfhydryl groups, and an inability of the visual pigment to be regenerated after bleaching. Regenerability after bleaching and the original pattern of sulfhydryl group reactivity are restored by addition of phosphatidylethanolamine to approximately 30 µmoles of phosphatidylethanolamine per µmole of rhodopsin. It is concluded that the properties of rhodopsin are sufficiently dependent upon associated phospholipid to support the view that rhodopsin is a lipoprotein.

Processus de photoréception rétinienne et thermodynamique des phénomènes irréversibles

L'étude de la constitution des segments externes des cellules visuelles et des caractéristiques essentielles de la photoréception rétinienne a suggéréla description d'un système thermodynamique ouvert dont te comportement a pueˆtre préciséàl'aide de la Thermodynamique des Phénomènes Irréversibles. On a pris en considération tes propriétés ATPasiques de la rhodopsine ou d'une protéineétroitement liéeàelle, ainsi que la possibilitéd'un transport ionique actif au niveau de la membrane des saccules aplatis. Les mécanismes dissipatifs proposés permettent une interprétation des phénomènes d'amplification des effets des photons isolés et de sensibilitédifférentielle des cellules photoréceptrices.

The dimensions of rod outer segments related to light absorption in the gecko retina

Для двyх видoв гeккoнoв, Gekko gekko и Eublifaris macularis,былa измepeнa плoщaдь ceтхaтки, зaнятaя нapyжными хлeникaми зpитeльных клeтoк (пoпepeхнoe ceхeниe) и былo нaйдeнo, хтo oнa для этих видoв cocтaвляeт cooтвeтcтвeннo 63 и 57%. Ha ocнoвaнии этих измepeний были pacхитaны плoтнocти зpитeльнoгo пигмeнтa пpи λmax для oтдeльных пaлoхeк и былo нaйдeнo, хтo oни paвны cooтвeтcтвeннo 0,58 и 0,71, a кoppигиpoвaнныe плoтнocти для вceй цeнтpaльнoй хacти ceтхaтки paвны cooтвeтcтвeниo 0,48 и 0,52. Эти пocлeдниe cooтвeтcтвyют cpeдним знaхeниям 67 и 70%, для пpoцeнтa cвeтa пoглoщaeмoгo пpи λmax вceй ceтхaткoй. Oбcyждaютcя oщибки, cвязaнныe c этими измepeниями.