Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Rod Cell Outer Segment”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources
PubMed1984

Localization of ATPases in retinal receptor cells.

Ouabain-sensitive, K-dependent p-nitrophenylphosphatase (K- NPPase ) activity of the Na-K-ATPase complex and the Ca-ATPase activity were studied ultracytochemically in the inner and outer segments of guinea pig photoreceptor cells by means of newly developed methods. The K- NPPase activity was demonstrated on the plasmalemma of the inner segments, whereas the Ca-ATPase activity was restricted to the matrix side of the inner membrane of the mitochondria which were accumulated in the inner segments. In contrast to the enzyme activities in the inner segments no such activity could be detected on the plasma and disk membranes of the outer segments. The functional meaning of the enzyme activities is discussed.

4-Nitrophenylphosphatase↗
PubMed1984

ADP-ribosylation of transducin by pertussis toxin blocks the light-stimulated hydrolysis of GTP and cGMP in retinal photoreceptors.

Cholera toxin and pertussis toxin catalyze ADP-ribosylation of the alpha-subunits of the GTP-binding stimulatory (Ns) and inhibitory (Ni) coupling components, respectively, of adenylate cyclase. Cholera toxin also catalyzes the ADP-ribosylation of transducin, the GTP-binding signal-coupling protein of retinal rod outer segments, and thereby reduces its light-stimulated GTPase activity. We show here that pertussis toxin also ADP-ribosylates transducin. Illumination markedly inhibits the ADP-ribosylation of transducin by pertussis toxin. ADP-ribosylation by this toxin in the dark is also lessened by prior incubation with hydrolysis-resistant GTP analogs. These inhibitory effects indicate that the GDP complex of transducin is the preferred form for ADP-ribosylation by pertussis toxin. Transducin modified by this toxin has a lower affinity for photoexcited rhodopsin than does unmodified transducin. ADP-ribosylation inhibits the light-stimulated GTPase activity of rod outer segments and blocks the signal-coupling activity of transducin in photoactivation of the phosphodiesterase. These and previous results show that cholera and pertussis toxins preferentially ADP-ribosylate the active (GTP-binding) and inactive (GDP-binding) conformations, respectively, of transducin. Correspondingly, ADP-ribosylation by these toxins inhibits GTPase activity by stabilizing transducin in the preferred active (GTP-binding) or inactive (GDP-binding) conformation. The actions of pertussis toxin on retinal rod outer segments provide further evidence for a high degree of homology between retinal transducin and the N proteins of the adenylate cyclase system.

Adenylate Cyclase Toxin↗
PubMed1996

Primary structure and expression of the human beta-subunit and related proteins of the rod photoreceptor cGMP-gated channel.

The full-length cDNA for the beta-subunit of the human rod photoreceptor cyclic nucleotide-gated channel has been shown to encode a 1251-amino acid ( approximately 140 kDa) polypeptide which, like its bovine counterpart, has an unusual bipartite structure. The C-terminal part corresponds to the previously reported "subunit 2" of the human rod channel and contains the structural features of other cyclic nucleotide-gated channel subunits including six putative membrane spanning segments, a cyclic nucleotide binding domain, a voltage-sensor motif, and a pore region. The N-terminal part contains the human homolog of the bovine glutamic acid-rich protein called GARP. Western blots indicate that both the native and heterologously expressed human beta-subunit migrate anomalously as a 220-kDa polypeptide by SDS-gel electrophoresis. Two other GARP variants, full-length GARP (f-GARP) and truncated GARP (t-GARP), are also present in human, bovine, and rat rod outer segments and migrate as 120-140- and 55-62-kDa polypeptides, respectively. The bovine f-GARP and t-GARP cDNAs code for proteins containing 590 amino acids and 299 amino acids, respectively. The first 571 amino acids of f-GARP and the first 291 amino acids of t-GARP are identical to the corresponding N-terminal amino acid sequence of the bovine beta-subunit. The two GARP variants, themselves, are not tightly associated with the rod channel. These results indicate that mammalian rod outer segments contain three alternatively spliced variants of GARP, one of which constitutes the N-terminal part of the rod channel beta-subunit.

Amino Acid Sequence↗
PubMed1991

Light damage in the rat retina: the effect of dietary deprivation of N-3 fatty acids on acute structural alterations.

We investigated the effect of depleting membrane docosahexaenoic acid (DHA, 22:6n-3) content through dietary deprivation of n-3 fatty acids on the susceptibility of the photoreceptors and pigment epithelium cells to acute light-induced changes. Male Sprague-Dawley rats were raised throughout gestation, lactation and up to the age of 8 weeks on semi-purified diets containing either safflower oil (SFO, n-3 deficient diet) or soybean oil (SO) as the sole source of lipids. A third group was switched at weaning from safflower oil to soybean oil (SFO/SO). Rats were maintained on a 12 hr/12 hr light/dark cycle in which the light level at the front of the cages was 5-10 lx. Light damage was produced by exposing dark-adapted animals to diffuse white fluorescent light of 700-800 lx for 30 min followed by 90 min of darkness. In order to study recovery from light damage, additional groups of SFO and SO rats were returned to dim cyclic light for 27 hr following bright light exposure. DHA content in retinal phosphatidylethanolamine and phosphatidylcholine was 65-75% lower in rats fed SFO than in rats fed SO. The decrease was compensated for by an increase in 22:5n-6, the total content of polyunsaturated fatty acids (PUFA) being similar in both the SFO and SO groups. The SFO/SO rats had DHA levels similar to SO animals, but 22:5n-6 remained elevated resulting in a slightly higher level of total PUFA. Severe rod outer segment (ROS) membrane disruptions were seen following bright light exposure in rats on the SO and SFO/SO diets. The appearance of these disruptions did not change significantly during more than 24 hr in dim cyclic light. In contrast, there were virtually no acute ROS lesions in the SFO group. Furthermore, there was a strong light-elicited disk-shedding response in the SO rats but not in the other two groups. The pigment epithelium of the DHA deficient retinas showed a significantly greater accumulation of large lipid droplets in the dark-adapted state. Notably, whole retina rhodopsin levels were 15% higher in the SFO than in the SO group. These results indicate that depletion of retinal DHA reduces the susceptibility of the rod outer segments to acute light damage and at the same time may alter visual pigment photochemistry and other photoreceptor and pigment epithelium functions.

Animals↗
PubMed1998

Calcium regulation of phototransduction in vertebrate rod outer segments.

The biochemical events underlying the phototransduction cascade in retinal photoreceptors of vertebrates are now well established, on the basis of a wealth of electrophysiological and biochemical evidence. In this review the Ca2+ regulation of the enzymes that generates the photoreceptor light response is analyzed, as well as the Ca2+ transport across the plasma membrane. Most of the results discussed in the following were collected from electrophysiological experiments.

Animals↗
PubMed1983

Photoreceptor fine structure in the domestic ferret.

The morphology of the retinal photoreceptors has been studied in the domestic ferret by electron microscopy. 2 types of photoreceptor are present and are differentiated morphologically into the classical categories of rods and cones. Rods are longer, more slender and more numerous than the cones. The rod outer segment is uniform in diameter along its entire length while the cone outer segment tapers distally. Cone outer segments are short and large apical processes from the pigment epithelium extend some distance to wrap around them. Both rods and cones possess a connecting cilium and a large cross-striated fibril which begins near the ciliary basal body and extends through the outer segment to end near the external limiting membrane. Cone nuclei are more vesicular than rod nuclei. They form a single layer immediately beneath the external limiting membrane while rod nuclei form several layers beneath the cone nuclei. The synaptic region of the cone cells is larger and more elaborate than that of the rods. Synapses in both rods and cones appear to be formed by both superficial and invaginated contacts.

Animals↗
PubMed1984

A barrier to lateral diffusion of porphyropsin in Necturus rod outer segment disks.

Microspectrophotometry was used to study lateral diffusion of the visual pigment, porphyropsin , in the disk membrane in intact mudpuppy (Necturus maculosus) rod outer segments (ROS), isolated in frog Ringer's solution. A concentration gradient of unbleached visual pigment was produced on the disks by rapidly photobleaching 40% of the pigment in an area spanning 1/4 or 1/2 of the cell's width. The change in optical density of the cells at 580 nm was then followed with time on either the bleached or unbleached side. The temperature dependence of porphyropsin diffusion yielded a Q10 of 2.5 between 10 and 20 degrees C with an activation energy of 12 +/- 2 kcal. At completion of pigment diffusion, the center and edge of the disk had, respectively, attained only 90 and 55% of the concentration expected. Computed diffusion coefficients (5.4 X 10(-9) cm2/s) were similar at the center and periphery of the disk immediately after the flash, however, an additional slow component for diffusion was detected at the periphery. A comparison of optical density at 525 nm along the diameter of ROS before and after the flash showed a persistent (20 min) postbleach concentration gradient of unbleached porphyropsin . This suggests that 15% of the prophyropsins may be sequestered into distinct areas on a mudpuppy disk and are not free to diffuse over the whole surface. This argument is supported by the observation that mudpuppy disks are separated into petal -shaped regions by incisures, some of which penetrate nearly to the disk center.

Animals↗
PubMed1992

Ultrastructural changes of the retina and the retinal pigment epithelium in Briard dogs with hereditary congenital night blindness and partial day blindness.

The offspring of two Briard dogs (brother and sister) with congenital, clinically stationary night blindness showed an aggravation of the disease with severe impairment of day vision in addition to night blindness. This ultrastructural study was performed on four such second generation puppies at the age of 4 months. The neuroretina and retinal pigment epithelium (RPE) from four locations were studied: the central area (immediately temporal to the optic disc); the centre of the tapetal area; the upper periphery (border of tapetal area); and the lower periphery (non-tapetal area). The RPE showed large inclusions, seemingly lipid in nature, mainly in the central and tapetal areas of the retina. Small, membrane bound, electron-dense inclusions were scattered in the RPE cytoplasm in all areas examined. The small inclusions were found to be less numerous in normal than in affected dogs and may be lysosomal in nature. Forty to fifty percent of the rod outer segments in the tapetal area showed disorientation of the disc membranes, whereas the corresponding figures were 20-40% in the central and lower peripheral areas and 6-25% in the upper peripheral area. No structural abnormalities were found in the rod inner segments or synaptic bodies. The cones were better preserved. The inner retina appeared normal. These electron microscopic findings seem to correspond to a previously published electrophysiologic evaluation, indicating a defective and delayed rod function (virtually no scotopic a- and b-waves), a better preserved cone function (photopic flicker responses present, although reduced) and impaired RPE activity (a prominent, slow negative potential of long latency at the site of the c-wave). It appears that these Briard dogs, showing structural changes of the rod outer segments in addition to pigment epithelial inclusions, mainly located in the posterior pole, comprise a pigment epitheliopathy and retinopathy morphologically different from other hereditary canine retinopathies that have been described earlier in the literature and different from animal models of congenital night blindness.

Animals↗
PubMed1990

Ca2+ binding capacity of cytoplasmic proteins from rod photoreceptors is mainly due to arrestin.

Arrestin (also called S-antigen or 48-kDa protein) binds to photoexcited and phosphorylated rhodopsin and, thereby, blocks competitively the activation of transducin. Using Ca2+ titration in the presence of the indicator arsenazo III and 45Ca2+ autoradiography, we show that arrestin is a Ca2(+)-binding protein. The Ca2+ binding capacity of arresting-containing protein extracts from bovine rod outer segments is about twice as high as that of arrestin-depleted extracts. The difference in the Ca2+ binding of arrestin-containing and arrestin-depleted protein extracts was attributed to arrestin. Both, these difference-measurements of protein extracts and the measurements of purified arrestin yield dissociation constants for the Ca2+ binding of arrestin between 2 and 4 microM. The titration curves are consistent with a molar ratio of one Ca2+ binding site per arrestin. No Ca2+ binding in the micromolar range was found in extracts containing mainly transducin and cGMP-phosphodiesterase. Since arrestin is one of the most abundant proteins in rod photoreceptors occurring presumably up to millimolar concentrations in rod outer segments, we suggest that aside from its function to prevent the activation of transducin, arrestin acts probably as an intracellular Ca2+ buffer.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2004

A novel tetraspanin fusion protein, peripherin-2, requires a region upstream of the fusion domain for activity.

Peripherin-2 (also known as peripherin/rds), a photoreceptor specific tetraspanin protein, is required to maintain normal cell structure through its role in renewal processes requiring membrane fusion. It is the first tetraspanin fusogen and has been shown to directly mediate fusion between disk membranes and opposing membranes to maintain the highly ordered structure of rod outer segments. Localized to the C terminus of human, bovine, and murine peripherin-2 is an amphiphilic fusion peptide domain (residues 312-326) and a highly conserved region upstream of this domain that we hypothesize is essential for fusogenic function. Our previous studies indicated that substitution of a threonine for a proline at position 296 within this highly conserved region enhanced fusion activity. In this study we wanted to determine whether this proline is essential with the introduction of three additional substitutions of proline with alanine, leucine, and glutamic acid. Wild type, P296T, P296A, P296L, and P296E mutants of peripherin-2 were expressed as His6-tagged full-length proteins in Madin-Darby canine kidney (MDCK) cells. All of the proteins were localized to intracellular membranes and detected as 42-kDa monomers by Western blot analysis. The wild type, P296A, and P296L assembled into core tetramers; in contrast the P296T and P296E formed higher order oligomers. Fusogenic activity of full-length protein expressed in MDCK membranes and purified protein reconstituted in model membrane liposomes was determined using fluorescence quenching techniques. Fusion activity was decreased in the P296L, P296A, and P296E mutants both in endogenous MDCK membranes and in model liposomes. Collectively, these results suggest that the proline at position 296 is necessary for optimal function.

Amino Acid Sequence↗
PubMed1981

Some indications of structural damage in retina by heavy ion radiation.

At the Lawrence Berkeley Laboratory Bevalac Facility, iron nuclei were accelerated to an energy of 600 MeV/amu. The beam of iron thus obtained was used to irradiate living biological specimens in order to study possible microscopic tissue damage with the aid of SEM. The experiments involved total head irradiation of live rats which were subsequently returned to their cages to remain for 1 day and 30 days before further examination. After the 1 day and 30 day waits, both eyes were enucleated and placed in chemical fixative followed by ethanol dehydration and critical point drying. Retinas were carefully removed from the eye cups and loaded separately on aluminum stubs which were sputter coated. SEM of the 1 day and 30 day retinas revealed lesions which were not found at all in control retinas. The 1 day and 30 day retinas manifest regions where outer rod segments were missing or rearranged. A single energetic iron nucleus may be capable of generating a retinal lesion which becomes enlarged as biological processes intervene during the 1 day and 30 day waits. Being composed of highly specialized nerve cells, retinas cannot regenerate following irradiation which severely damages the rod cells. Thus one would expect the observed radiation induced retinal lesions to correspond to permanent tissue damage and possible loss of visual acuity in the intact animal.

Animals↗
PubMed1985

The 3, 4-didehydroretinal chromophore of goldfish porphyropsin.

The isomeric configuration of the 3,4-didehydroretinal chromophore of goldfish porphyropsin was determined by high performance liquid chromatography (HPLC) and by the regeneration of this visual pigment with authentic isomers of 3,4-didehydroretinal. A nonisomerizing, quantitative method using hydroxylamine and methylene chloride was employed to extract the 3,4-didehyroretinal chromophore from the rod outer segment membrane (containing the porphyropsin). When this extracted chromophore was injected into the HPLC, only a single major peak was observed and this peak coeluted with the authentic 11-cis 3,4-didehydroretinyl oxime. This suggests that the chromophore of goldfish porphyropsin is 11-cis 3,4-didehydroretinal. When the bleached rod outer segments (containing the opsin) were incubated with different 3,4-didehydroretinal isomers (13-cis, 11-cis, 9-cis, and all-trans), only the 11-cis isomer resulted in the degeneration of porphyropsin. This also suggests that the porphyropsin chromophore exists in the 11-cis configuration.

Animals↗
PubMed1994

Insulin stimulation of retinal outer segment uptake by cultured human retinal pigment epithelial cells determined by a flow cytometric method.

This study investigates the mechanism by which insulin stimulates phagocytosis in cultured human retinal pigment epithelium, using a flow cytometric assay of retinal outer segment uptake. RPE cells were isolated from adult human donors and grown in culture. Retinal outer segments were isolated from fresh bovine eyes and covalently labeled with the fluorescent dye carboxy-SNAFL-2. Retinal outer segment binding and uptake was quantified by direct visualization and the increase in cellular fluorescence measured using a flow cytometer and the methods compared. Uptake measured by flow cytometry was further characterized by concentration, time, temperature and serum stimulation, and shown to be comparable to other published methods. Uptake of retinal outer segments was acutely stimulated by insulin in the absence or presence of serum with half maximal stimulation occurring between 0.1 and 1.0 microgram ml-1. Theophylline, forskolin and cholera toxin all reduced retinal outer segment uptake by RPE cells, but had no effect upon insulin stimulation. Measurements of cAMP showed that insulin did not change intracellular cAMP concentration compared to controls in the absence or presence of added retinal outer segments. One hundred nanomolar okadaic acid also inhibited retinal outer segment uptake but not insulin-stimulated uptake, nor did 100 microM genistein have an effect upon insulin-stimulated uptake. Preincubation of RPE cells with 25 microM ZnCl2 overnight stimulated retinal outer segment uptake and appeared to inhibit the insulin stimulation. Preincubation of the cells in 25 mM glucose overnight also increased the uptake of retinal outer segments over control and reduced the effect of insulin. We conclude that insulin stimulates retinal outer segment phagocytosis by an as yet unknown process which may involve specific tyrosine phosphatases.

Cells, Cultured↗
PubMed1992

Studies on the interaction of alpha subunits of GTP-binding proteins with beta gamma dimers.

The interaction of several preparations of purified beta gamma dimers with two types of guanosine-nucleotide-binding-regulatory-(G)-protein alpha subunits, a recombinant bv alpha i3, made in Sf9 Spodoptera frugiperda cells by the baculovirus (bv) expression system, and alpha s, either purified from human erythrocyte Gs-type GTP-binding protein, and activated by NaF/AlCl3, or unpurified as found in a natural membrane, were studied. The beta gamma dimers used were from bovine rod outer segments (ROS), bovine brain, human erythrocytes (hRBC) and human placenta and contained distinct ratios of beta subunits that, upon electrophoresis, migrated as two bands with approximate M(r) of 35,000 and 36,000, as well as distinct complements of at least two gamma subunits each. When tested for their ability to recombine at submaximal concentrations with bv alpha i3, ROS, brain, hRBC and placental beta gamma dimers exhibited apparent affinities that were the same within a factor of two. When bovine brain, placental and ROS beta gamma dimers were tested for their ability to promote deactivation of Gs, brain and placental beta gamma dimers were equipotent and at least 10-fold more potent than that of ROS beta gamma dimers; likewise, brain beta gamma and placental dimers were equipotent in inhibiting GTP-activated and GTP-plus-isoproterenol-activated adenylyl cyclase, while ROS beta gamma dimers were less potent when assayed at the same concentration. The possibility that different alpha subunits may distinguish subsets of beta gamma dimers from a single cell was investigated by analyzing the beta gamma composition of three G proteins, Gs, Gi2 and Gi3, purified to near homogeneity from a single cell type, the human erythrocyte. No evidence for an alpha-subunit-specific difference in beta gamma composition was found. These findings suggests that, in most cells, alpha subunits interact indistinctly with a common pool of beta gamma dimers. However, since at least one beta gamma preparation (ROS) showed unique behavior, it is clear that there may be mechanisms by which some combinations of beta gamma dimers may exhibit selectivity for the alpha subunits they interact with.

Adenosine Diphosphate Ribose↗
PubMed2000

Dietary 20:4n-6 and 22:6n-3 modulates the profile of long- and very-long-chain fatty acids, rhodopsin content, and kinetics in developing photoreceptor cells.

The objective of this study was to determine whether addition of dietary 20:4n-6 and 22:6n-3 to a conventional infant formula fat blend influences membrane long-chain and very-long-chain fatty acid composition, rhodopsin content, and rhodopsin kinetics in developing rat photoreceptor cells. The dietary fats were formulated based on the fat composition of a conventional infant formula providing an 18:2n-6/18:3n-3 ratio of 7:1 (SMA, Wyeth Nutritionals), which served as the control fat blend. This dietary fat blend was modified to contain 20:4n-6 [arachidonic acid (AA)], 22:6n-3 [docosahexaenoic acid (DHA)], AA + DHA, or an 18:2n-6/18:3n-3 ratio of 4:1 (alpha-linolenic acid). Dams were fed diets from birth, and rat pups were fed the same diet after weaning. Retinas and rod outer segments were prepared in the dark from pups at 2, 3, and 6 wk of age for fatty acid analysis of individual phospholipids, rhodopsin content, and rhodopsin disappearance kinetics after light exposure. Feeding AA + DHA in the diet increased 22:6n-3 levels in phosphatidylcholine and phosphatidylethanolamine. In phosphatidylcholine, total n-6 tetraenoic very-long-chain fatty acids and total n-3 pentaenoic and n-3 hexaenoic very-long-chain fatty acids increased after feeding AA and DHA, respectively. Developmental changes were characterized by a decrease in 20:4n-6 in the major phospholipids, whereas 22:6n-3 increased with age in rod outer segments. The highest rhodopsin content occurred in the retina of rats fed diets containing AA and/or DHA. The kinetics of rhodopsin disappearance after light exposure was highest in rats fed DHA at 6 wk of age. This study demonstrates that small manipulations of the dietary level of 20:4n-6 and 22:6n-3 are important determinants of fatty acid composition of membrane lipid and visual pigment content and kinetics in the developing photoreceptor cell.

Animals↗
PubMed1993

A comparison of phagocytosis by the retinal pigment epithelium in normal and delayed amelanotic chickens.

The retinal pigment epithelium (RPE) performs a critical role in maintaining the integrity and renewal of the retinal system by clearing the shed photoreceptor outer segment debris through the process of phagocytosis. If phagocytosis is impaired, accumulation of the debris occurs leading to the degeneration of the retina. Phagocytosis, measured by polyvinyl toluene bead uptake is a normal cell activity exhibited by the embryonic retinal pigment epithelium even before complete differentiation of the neuronal layers. It is significant that embryonic pigment epithelium from either normal or delayed amelanotic (DAM) strain is competent in the process of non-specific particle uptake. In normal chickens non-specific phagocytic activity is observable as early as embryonic day 9 and continues through the rest of the developmental period and throughout adult life. The retinal pigment epithelium in DAM chickens exhibits early phagocytic activity at embryonic day 9 and then through day 16, but by day 19 this function is lost. This loss of phagocytic capacity in RPE of the DAM strain precedes and may be instrumental in the gradual retinal degeneration exhibited by these animals. Specific phagocytosis of rod outer segments (ROS) was examined in 4-week-old post-hatch normal and DAM RPE. Phagocytosis of ROS was greatly reduced in DAM RPE implying that the defect in the DAM is expressed in non-specific and specific phagocytosis. This study indicates that the DAM retinal system can now serve as an alternative and comparative model for studying different aspects of retinal degeneration.

Animals↗
PubMed1995

Ultrastructural features of retinal dystrophy in mutant vitiligo mice.

Ultrastructural features of the retinal pigment epithelium and photoreceptor cells were studied in vitiligo (C57BL/6 mivit/mivit) mice. Eyes from 12-day- to 56-week-old animals were analysed. Abnormal photoreceptors were seen in 12-day-old mice. By 3 weeks malformed outer segments were evident in the posterior and equatorial retina, but normal photoreceptors were present in the periphery. By 28 weeks, a marked gradient in cell loss was evident, with a progressive increase in cell viability along the posterior-peripheral axis. Viable intact photoreceptors were still present in the peripheral retina of 56-week-old mice. Melanosome content varied between adjacent pigment epithelium cells in both the posterior and peripheral retina. In the choroid, however, a steep posterior-peripheral gradient in melanosome content was evident with highest pigmentation in the periphery. In the optic nerve head region abnormal development of photoreceptors was correlated with proliferation of abnormal pigment epithelium cells. Accumulation of rod outer segment debris in the posterior and peripheral subretinal space preceded photoreceptor cell death. Short pigment epithelial microvilli without proper attachment to photoreceptors are suggestive of alterations in pigment-epithelium-photoreceptor interaction, which might affect photoreceptor differentiation and phagocytosis of rod outer segments by pigment epithelium cells.

Animals↗