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PubMed1980

Surface and cytoplasmic antigens in retinoblastoma.

Surface and cytoplasmic antigens in retinoblastoma were examined by antisera prepared against two tissue-cultured retinoblastoma cell lines. In addition, several other antisera, including anti-rhodopsin, anti-rod outer segment, anti-large-molecular-weight protein, anti-S, and anti-P antigen, were also utilized in a complement-dependent cytotoxicity assay in order to explore the tumor cell surface. Antisera to tissue-cultured retinoblastoma cell lines were cross-reactive to both cell lines as was rod outer segment antiserum.

Antigens, Neoplasm↗
PubMed2003

Retarded outer segment development in TrkB knockout mouse retina organ culture.

PURPOSE: To determine the effects of trkB deficiency in the mouse retina on photoreceptor development and retinal organization, in the absence of confounding systemic effects. METHODS: Newborn mice that carried two null trkB alleles (trkB-/-) and their wild type (WT) littermates were used for retinal organ cultures. On Day 21, rod development was assessed histologically in plastic sections (outer segment length) and retinal organization was analyzed using retinal cell-type specific antibodies. Anatomical data obtained from the organ cultures were compared to previously published histological results from in vivo data. RESULTS: (1) Rod outer segment length was significantly shorter in retinas from trkB-/- mice in the presence of normal numbers of rods. (2) No dopaminergic amacrine cells were observed in the knockout retina. (3) Unlike in the in vivo condition, recoverin-positive OFF-cone bipolar cells were present in trkB-/- retinas grown in culture. CONCLUSIONS: (1) These results demonstrate that rod outer segment development is compromised in the absence of trkB in the retina. (2) This study further supports our previous conclusion that the elimination of trkB expression alters rod development, because the presence of trkB receptors within the retina is essential for normal rod maturation and not because of confounding systemic effects. (3) More generally, this study stresses the importance of investigating complex phenotypes in gene knockout mice under conditions that isolate the organ under investigation from unrelated systemic variations.

Animals↗
PubMed1993

Visual transduction in dialysed detached rod outer segments from lizard retina.

1. Properties of a new preparation for studying the physiology and biochemistry of phototransduction in retinal rods are described. Whole-cell voltage clamp was used to record the generation, maintenance and light-sensitivity of dark current in rod outer segments that had been isolated from the rest of the receptor cell by detachment at the connecting cilium. 2. Detached outer segments dialysed with standard internal solution supplemented with physiological amounts of ATP (5 mM) and GTP (1 mM) developed a standing inward dark current that was the sum of three components: approximately 91% light-sensitive current, approximately 6% Na(+)-Ca2+,K+ exchange current and approximately 3% leakage current. Light-sensitive dark current (mean amplitude approximately -63 pA) was suppressed transiently by brief flashes in an intensity-dependent manner. Light responses had the same kinetics, sensitivity and intensity-response relationship as those recorded from intact rods. 3. Dialysed outer segments differed from intact rods in that intense flashes evoked saturating responses that recovered incompletely to a plateau of reduced dark current caused by incomplete inactivation of the transduction cascade. Light sensitivity was reduced for a short time following an intense flash and then recovered despite persistent reduction of dark current. This suggests that there is no fixed relationship between dark current amplitude and light sensitivity. 4. Light-sensitive dark current faded rapidly when outer segments were not supplied with nucleotides. Outer segments dialysed with solution that contained cyclic GMP, but no ATP or GTP, supported dark current at a level that increased with [cyclic GMP]. When basal phosphodiesterase (PDE) activity is inhibited, 8 microM cyclic GMP supports a dark current of approximately 70 pA. 5. Light sensitivity decreased during recordings made with solution that contained only cyclic GMP, consistent with the inhibition of G protein activation by loss of GTP. After thorough nucleoside triphosphate depletion, however, intense illumination evoked a transient increase rather than a decrease in dark current, i.e. an inverted light response. This result suggests that isomerized rhodopsin may generate a signal that causes either inhibition of basal PDE activity or release of bound cyclic GMP. 6. Sustained Na(+)-Ca2+,K+ exchange current was recorded during steady illumination when Ca2+, but not when Mg2+, was added to the dialysis solution. Exchange current increased with the amount of added Ca2+ and saturated at approximately 18 pA when the dialysis solution contained > or = 10 mM Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed2001

Rod outer segments mediate mitochondrial DNA damage and apoptosis in human retinal pigment epithelium.

PURPOSE: To investigate the interrelationships between DNA damage, mitochondrial activity, and apoptosis in retinal pigment epithelial cells (RPE) after exposure to rod outer segments (ROS). METHODS: After incubation of cultured human RPE with ROS, mitochondrial redox function was evaluated from MTT reduction. Mitochondrial (mt) and nuclear (n) DNA damage were determined by quantitative polymerase chain reactions (QPCR). Apoptotic RPE cells were detected by binding of annexin V to phosphatidyl serine (PS) using fluorescence microscopy. The expression of the pro-apoptotic proteins, p53 and p21(waf-1), and DNA repair enzymes, apurinic/apyrimidinic endonuclease (APE(ref-1)) and DNA polymerase beta (beta-pol) were quantitatively determined by Western blotting analysis. RESULTS: Mitochondrial function decreased by 20 +/- 5% and annexin V immunofluorscent binding was enhanced after exposure of cells to physiological levels of ROS (3.8 x 10(6)cm(-2)) for 4 h. MtDNA was preferentially damaged after exposure to ROS with increased lesion frequencies of 1.49 +/- 0.37 and 2.2 +/- 0.14 per 10 kb base pairs (bp), respectively after 5 and 7 h contact, compared to untreated controls (zero class damage). APE(ref-1)expression increased more than 340% above controls after exposure to ROS for 7 and 24 h. The expression of beta-pol in cultures increased 110% above controls after 24 h contact with the ROS. The expression of p53 and p21 in cells increased 100 and 38% above controls after 24 h exposure to the ROS. CONCLUSIONS: Exposure of ROS to ROS induced mtDNA damage and dysfunction and activated nDNA repair pathways, which did not prevent apoptosis.

Animals↗
PubMed1989

Extrusion of calcium from rod outer segments is driven by both sodium and potassium gradients.

Calcium is transported across the surface membrane of both nerve and muscle by a Na+-dependent mechanism, usually termed the Na:Ca exchange. It is well established from experiments on rod outer segments that one net positive charge enters the cell for every Ca2+ ion extruded by the exchange, which is generally interpreted to imply an exchange stoichiometry of 3 Na+:1 Ca2+. We have measured the currents associated with the operation of the exchange in both forward and reversed modes in isolated rod outer segments and we find that the reversed mode, in which Ca2+ enters the cell in exchange for Na+, depends strongly on the presence of external K+. The ability of changes in external K+ concentration ([K+]o) to perturb the equilibrium level of [Ca2+]i indicates that K+ is co-transported with calcium. From an examination of the relative changes of [Ca2+]o, [Na+]o, [K+]o and membrane potential required to maintain the exchange at equilibrium, we conclude that the exchange stoichiometry is 4 Na+:1 Ca2+, 1 K+ and we propose that the exchange should be renamed the Na:Ca, K exchange. Harnessing the outward K+ gradient should allow the exchange to maintain a Ca2+ efflux down to levels of internal [Ca2+] that are considerably lower than would be possible with a 3 Na+:1 Ca2+ exchange.

Algorithms↗
PubMed1998

Effect of rhodopsin C-terminal peptide on photoresponses in functionally intact rod outer segments.

The protein-protein interactions that underlie shut-off of the light-activated rhodopsin were studied using synthetic peptides derived from C-terminal region of the rhodopsin. The photoresponses were recorded in whole-cell voltage clamp from rod outer segments (ROS) that were internally dialyzed with an intracellular solution containing the synthetic peptides. This was the first time that synthetic peptides have been used in functionally intact ROS. None of the tested peptides promoted the shut-off of the photolyzed rhodopsin (R) by stimulating the binding of an activated arrestin to non-phosphorylated R, contrary to what was expected from in vitro experiments (Puig et al. FEBS Lett. 362: 185-188, 1995).

Adenosine Triphosphate↗
PubMed1986

Phosphorylation reactions in bovine rod outer segments studied by 32P-labelling of intact retina.

The protein phosphorylation pattern in the intact bovine retina has been investigated by labelling with 32P-phosphate under incubation conditions that preserve the electrical photoresponse of the photoreceptor cells. The phosphorylation of rod outer segment proteins was analysed after isolation of outer segments from the labelled retina. The global influence of light, Ca2+ and the phosphodiesterase inhibitor, isobutylmethylxanthine, on protein phosphorylation in rod outer segments was analysed. A 12 kDa protein is the most prominent phosphorylated species in the intact bovine retina. Its phosphorylation is increased by light and/or Ca2+. Evidence is presented that this strongly phosphorylated protein is not located in the outer segment, and we suggest that it may be a synaptic protein. Retinal rod outer segment membrane proteins with apparent molecular weights of 245, 226, 125, 110, 50, 46, 38 and 20 all show light-stimulated phosphorylation. Lowering the extracellular Ca2+ levels results in a decrease of the phosphorylation level of some of these proteins, viz. at 125, 50, 38 and probably at 20 kDa. Such proteins, whose phosphorylation level is influenced both by light and by elevated Ca2+, are candidates for mediators of phototransduction. The phosphorylated species at 245, 226, 110, 50 and 20 kDa are enriched in rod outer segment plasma membrane preparations. These protein species could participate in the light-regulated modulation of the Na+-conductance of the plasma membrane.

1-Methyl-3-isobutylxanthine↗
PubMed1997

Fusion of intracellular rod outer segment disk membranes with the surrounding plasma membrane.

PURPOSE: The series of experiments described were undertaken to evaluate the use of a cell-free lysis model to measure membrane fusion events in photoreceptor rod outer segments (ROS). The experiments measure fusion initiated with the osmotic disruption of fluorescenty-labeled ROS and correlate these findings with previously described disc-plasma membrane fusion. The influence of calcium and disc membrane cholesterol content on fusion between ROS membrane species was evaluated. METHODS: Membrane fusion was followed by measuring the dilution of a membrane-associated fluorophore (R18) from labeled plasma membrane to an unlabeled membrane species; discs. Free calcium in the ROS preparations was measured using the calcium-sensitive fluorophore Quin-2. The affects of cholesterol content on fusion were investigated by increasing and decreasing disc membrane cholesterol content using well established lipid exchange techniques. RESULTS: There is an increase in R18 fluorescence on hypotonic lysis of ROS whose plasma membrane is labeled with R18. This increase in fluorescence is inhibited by EGTA and requires nanomolar levels of calcium. The initial rates of fusion between R18-labeled plasma membrane and discs were virtually identical in discs with increased and decreased levels of membrane cholesterol. CONCLUSIONS: The increase in R18 fluorescence on lysis of R18-labeled ROS is consistent with fusion between disc membranes and the surrounding plasma membrane. This fusion is dependent on nanomolar levels of calcium, is inhibited by EGTA, and is independent of the cholesterol content of these membranes.

Aminoquinolines↗
PubMed2000

Identification and characterization of all-trans-retinol dehydrogenase from photoreceptor outer segments, the visual cycle enzyme that reduces all-trans-retinal to all-trans-retinol.

Retinol dehydrogenase (RDH), the enzyme that catalyzes the reduction of all-trans-retinal to all-trans-retinol within the photoreceptor outer segment, was the first visual cycle enzymatic activity to be identified. Previous work has shown that this enzyme utilizes NADPH, shows a marked preference for all-trans-retinal over 11-cis-retinal, and is tightly associated with the outer segment membrane. This paper reports the identification of a novel member of the short chain dehydrogenase/reductase family, photoreceptor RDH (prRDH), using subtraction and normalization of retina cDNA, high throughput sequencing, and data base homology searches to detect retina-specific genes. Bovine and human prRDH are highly homologous and are most closely related to 17-beta-hydroxysteroid dehydrogenase 1. The enzymatic properties of recombinant bovine prRDH closely match those previously reported for RDH activity in crude bovine rod outer segment preparations. In situ hybridization and RNA blotting show that the PRRDH gene is expressed specifically in photoreceptor cells, and protein blotting and immunocytochemistry show that prRDH localizes exclusively to both rod and cone outer segments and that prRDH is tightly associated with outer segment membranes. Taken together, these data indicate that prRDH is the enzyme responsible for the reduction of all-trans-retinal to all-trans-retinol within the photoreceptor outer segment.

Alcohol Oxidoreductases↗
PubMed1998

Fusion between retinal rod outer segment membranes and model membranes: a role for photoreceptor peripherin/rds.

Peripherin/rds plays an essential role in the maintenance of photoreceptor rod cell disk membrane structure. The purification of this protein to homogeneity [Boesze-Battaglia, K., et al. (1997) Biochemistry 36, 6835-6846] has allowed us to characterize the functional role of peripherin/rds in the maintenance of rod outer segment (ROS) membrane fusion processes. Utilizing a cell-free fusion assay system, we report that the fusion of R18-labeled ROS plasma membrane (R18-PM) with disk membranes or peripherin/rds-enriched large unilammellar vesicles (LUVs) is inhibited upon trypsinolysis of peripherin/rds. To understand this phenomenon, we tested the ability of a series of overlapping synthetic C-terminal peripherin/rds peptides to mediate model membrane fusion. Within the 63 amino acid long region of the C-terminus, we identified a minimal 15 residue long amino acid sequence (PP-5), which is necessary to promote membrane fusion. PP-5 was able to inhibit R18-PM disk membrane fusion and promoted ANTS/DPX contents mixing in a pure vesicle system. This peptide (PP-5) promoted calcium-induced vesicle aggregation of phosphatidylethanolamine:phosphatidylserine LUVs. FTIR analysis confirmed the structural prediction of this peptide as alpha-helical. When modeled as an alpha-helix, this peptide is amphiphilic with a hydrophobicity index of 0.75 and a hydrophobic moment of 0.59. PP-5 has substantial biochemical and functional homology with other well-characterized membrane fusion proteins. These results demonstrate the necessity for peripherin/rds in ROS membrane fusion, specifically the requirement for an intact C-terminal region of this protein.

Amino Acid Sequence↗
PubMed1987

Monensin stimulates glycerolipid incorporation into rod outer segment membranes.

Monensin is an ionophore which disrupts the structure of the Golgi apparatus and inhibits vesicular transport in eukaryotic cells. In this study, we examined the effects of monensin on the incorporation of newly synthesized glycerolipids into retinal rod outer segment (ROS) membranes. Frog retinas were incubated in the presence or absence of monensin (50 nM) with either [1,2,3-3H]glycerol or [9,10-3H]palmitic acid as radiolabeled substrate. Total lipids were extracted from retinas and ROS membranes and resolved into individual phospholipid classes and neutral lipids by thin-layer chromatography. In the presence of monensin, the specific activity of ROS phospholipids was increased about 2-fold with [3H]glycerol and nearly 3-fold with [3H]palmitate as substrates relative to controls. In contrast, the specific activity of total retinal lipids, the relative incorporation of label into ROS and retinal phospholipids, and the total lipid phosphorous content of ROS membranes and retinas were not significantly different from control values. These data suggest that the enhanced labeling of ROS phospholipids in the presence of monensin was due to altered intracellular routing of lipids rather than increased glycerolipid synthesis. Under the same conditions, total retinal protein synthesis was about 90% of control, but light microscopic autoradiography indicated that newly synthesized proteins were not transported to the ROS for assembly into disc membranes. Thus, newly synthesized glycerolipids can be delivered to the ROS by a mechanism which is independent of protein transport to that cellular compartment.

Animals↗
PubMed1997

Iris pigment epithelial cells of long evans rats demonstrate phagocytic activity.

The phagocytic activities of iris pigment epithelial (IPE) cells and retinal pigment epithelial (RPE) cells of Long Evans rats towards latex beads and rod outer segments (ROS) were compared in vitro. IPE and RPE cells of Long Evans rats were isolated and pure cultures obtained. The cultures were incubated with latex beads, fixed, and analysed computer morphometrically, IPE and RPE cell cultures were also incubated with isolated ROS and examined using transmission electron microscopy. IPE cells were able to ingest latex beads. There was no significant difference between the number of latex particles phagocytized by IPE and RPE cells. After incubation with isolated ROS, IPE cells also recognized and ingested the ROS particles. However, the specific phagocytic capacity of IPE cells was 76% of that of RPE cells. The autologous IPE cells might have the potential to be used as an alternative to RPE cells for transplantation in the subretinal space.

Animals↗
PubMed1999

Longitudinal spread of second messenger signals in isolated rod outer segments of lizards.

1. In vertebrate rods activation of the phototransduction cascade by light triggers changes in the concentrations of at least two diffusible intracellular second messengers (cGMP and Ca2+) whose actions depend on how far they spread from their site of production or entry. To address questions about their spatial spread, cell-attached patch current recording and fluorescence imaging of Calcium Green-dextran were used to measure the longitudinal spread of cGMP and Ca2+, respectively, in functionally intact isolated Gecko gecko lizard rod outer segments under whole-cell voltage clamp. 2. The light-evoked changes in cGMP and Ca2+ concentrations decayed with distance from a site of steady focal activation by two-photon absorption of 1064 nm light with similar decay lengths of approximately 3.5 microm. 3. These results can be understood on the basis of a quantitative model of coupled diffusible intracellular messengers, which is likely to have broad relevance for second messenger signalling pathways in general. 4. The decay length for the spread of adaptation from a site of steady local illumination was about 8 microm, i.e. substantially longer than the decay lengths measured for the spread of cGMP and Ca2+. There are a number of factors, however, that could broaden the apparent relationship between functional changes in the light response and the concentration of a diffusible messenger. For these reasons the measured decay length is an upper limit estimate of the spread of adaptation and does not rule out the possibility that Ca2+ and/or cGMP carry the adaptation signal.

Adaptation, Physiological↗
PubMed1995

Hyperthermia accelerates retinal light damage in rats.

PURPOSE: To study the time course of visual cell damage resulting from hyperthermic light exposure and the possible involvement of rod outer segment (ROS) lipids in the process. METHODS: Rats were acclimated in darkness for 2 hours in a hyperthermic chamber to elevate core body temperature and then exposed to intense green light for up to 4 hours during hyperthermia. After light exposure, the animals were either sacrificed immediately for biochemical or morphologic analysis of retinal light damage or returned to darkness for up to 2 weeks at ambient temperature before analysis. Rod outer segment lipid profiles were characterized, and visual cell loss was determined by rhodopsin and visual cell DNA measurements. Morphology was performed at the light and electron microscopic level. RESULTS: Retinal damage resulting from hyperthermic light exposure was found to be temperature, time, and light intensity dependent. At an elevated environmental temperature of 34.5 degrees, 50% visual cell loss was found after 1.5 hours of 1100 lux light exposure; the same degree of visual cell loss occurred after only 1 hour when rats were maintained at 37 degrees C. At ambient temperatures, 4 hours of light exposure had no effect on visual cell loss. Irrespective of environmental temperature, when rats were maintained in darkness no visual cell loss occurred. Whereas docosahexaenoic acid (22:6) was unchanged in the purest fraction of ROS isolated immediately after light treatment, a 5 mol% loss of the polyunsaturated fatty acid was found in ROS isolated 2 or 24 hours after light exposure. Rod outer segment lipid composition was largely unaffected by hyperthermic light exposure, but the density of some ROS increased. Morphologically, the ROS appeared to be nearly normal immediately after hyperthermic light exposure and structurally more abnormal 2 and 24 hours later. The retinal pigment epithelium exhibited damage immediately after exposure, which also increased 2 and 24 hours later. CONCLUSIONS: Hyperthermia in rats dramatically accelerates retinal light damage compared with light exposure under euthermic conditions. Over loss of ROS 22:6 does not occur during hyperthermic light exposure, but it is apparent during the 24-hour period after light treatment. This suggests that the disappearance of 22:6 from ROS occurs in tandem with the process of visual cell death resulting from retinal light damage.

Animals↗
PubMed1999

Comparative study of ROS degradation by IPE and RPE cells in vitro.

BACKGROUND: The aim of this study was to compare the degradation of rod outer segments (ROS) in porcine iris pigment epithelial cells (IPE) and retinal pigment epithelial (RPE) cells by measuring the increase of lipofuscin-like fluorescence. METHODS: We measured the development of autofluorescence of lipofuscin-like material in living cells over a period of 4 weeks using an image-analyzing system comprising a light microscope, a filter set with an appropriate wavelength for the detection of lipofuscin-like autofluorescence and a silicon-intensified target camera connected to a computer. The lipofuscin-like fluorescence was quantified as the mean gray value of pixels over a defined area in the cell. In addition, ultrastructural examination of the cells was performed using transmission electron microscopy. RESULTS: We found that while both cell types had increased autofluorescence over time, the increase of lipofuscin-like fluorescence was significantly higher in IPE cells than in RPE cells. The ultrastructure of both cell types was similar and no accumulation of lipofuscin-like granules was observed. CONCLUSION: These findings suggest that although IPE cells are able to phagocytize ROS, their ability to degrade them may be lower than in RPE cells. The increase of lipofuscin-like fluorescence is not due to the accumulation of lipofuscin-like granules.

Animals↗
PubMed1987

Cytochemical localization of Mn2+-dependent pyrimidine 5'-nucleotidase activity in isolated rod outer segments.

A cytochemical method was developed for localization in isolated rod outer segments of manganese-dependent pyrimidine 5'-nucleotidase (MDPNase), an enzyme activity with possible relevance to shedding that we recently reported in photoreceptors and retinal pigment epithelial (RPE) cells in the intact rat retina. The purpose of this study was to eliminate the possibility that the previously observed cytochemical staining of the rods was due to diffusion of reaction product from the RPE cell lysosomes, which were also heavily stained. Rod outer segments (ROS) were isolated on continuous sucrose gradients from retinal homogenates prepared from rats raised in cyclic light (12 hr light:12 hr dark) and killed during the first 2 hr after light onset. ROS-containing bands were removed from the gradients and the isolated rods were fixed in 0.25% glutaraldehyde and pelleted. Chopped sections of the pellets were incubated in cytochemical medium for MDPNase activity and processed for light- and electron-microscopic localization of the enzyme activity. Two patterns of cytochemical staining were seen in ROS isolated from retinas obtained at this time of day. A few of the pellets contained clusters of ROS that were heavily coated along their surfaces and seemingly interconnected by thick strands of highly reactive extracellular material that displayed a punctate pattern of cytochemical staining. This material may have originated from the apical processes of the RPE cells, which were heavily stained in tissue fixed in situ around the time of light onset. The second staining pattern, visible only by electron microscopy, was more commonly observed. In the majority of the isolated ROS profiles, discrete streaks of cytochemical reaction product were seen in association with the internal aspects of the discs, at sites that seemed to correspond to the rims, and to narrow zones within the disc interiors. This distribution of reactive sites closely resembled that observed over most of the length of the ROS in the intact retina fixed at the same time of day. Occasionally, ROS profiles were encountered in which additional reactive sites were localized to the interdisc spaces between the plasma membrane and the rims of the discs. The latter pattern resembled the distribution of reaction product seen during this period over the tips of the ROS fixed in situ. As in the intact retinas, the cytochemical staining of the isolated ROS was inhibited by fluoride ions and strongly stimulated by manganese ions.(ABSTRACT TRUNCATED AT 400 WORDS)

5'-Nucleotidase↗
PubMed2004

Basement membrane-dependent modification of phenotype and gene expression in human retinal pigment epithelial ARPE-19 cells.

PURPOSE: To use porcine lens capsule (PLC) as basement membrane for ARPE-19 cells and to characterize its effects on cell differentiation and gene expression. METHODS: Postconfluent cultures of ARPE-19 cells were established on either porous polyester filters or PLC membranes and characterized by electron microscopy, immunocytochemistry, and transepithelial electrical resistance measurements. Metabolic activity was assessed by measuring phagocytosis of rod outer segments. mRNA populations of ARPE-19 cells grown on polyester and PLC membranes were compared by suppressive subtractive hybridization. Differentially regulated messages were subsequently identified by DNA sequencing and their altered expression confirmed by Northern or virtual Northern blot analysis. RESULTS: Culture of ARPE-19 cells on PLC membrane induced the formation of apical microvilli and the ability to phagocytose rod outer segments. These culture conditions also led to enhanced junctional distribution of ZO-1 and occludin, the formation of polarized membrane domains, and a significant increase in transepithelial resistance. Gene expression was significantly altered by growth on PLC membranes and 29 differentially expressed transcripts were identified. CONCLUSIONS: Culture of ARPE-19 cells on PLC membranes resulted in a more differentiated phenotype and in expression of a specific set of transcripts encoding protein products that may affect epithelial differentiation, polarity and survival.

Animals↗
PubMed1991

Evidence for an insulin-like growth factor autocrine-paracrine system in the retinal photoreceptor-pigment epithelial cell complex.

The interphotoreceptor matrix (IPM), lying between retinal photoreceptor and pigment epithelial (RPE) cells, contains insulin-like growth factor I (IGF-I) immunoreactivity that co-elutes with authentic human IGF-I in HPLC analyses. Cultured human RPE cells synthesize and release IGF-I, raising the possibility that the RPE serves as a source of IPM IGF-I in vivo. Photoreceptor rod outer segments and cultured monkey RPE cells express specific IGF-I receptors with alpha-subunits of 120 and 138 kDa, respectively. They thus appear to be of the "brain" (in photoreceptors) and "peripheral" (in RPE cells) receptor subtypes. Additionally, the IPM contains high levels of an IGF binding protein (IGF-BP) that specifically binds IGF-I and IGF-II. The IPM-BP is visualized as a single radiographic band by both ligand blot and affinity cross-linking procedures. With enzymes specific for removing N- and O-linked oligosaccharides, the IPM-BP was found to contain O- but not N-linked glycosylated side chains. The distinctive size and glycosylation pattern of the IPM-BP indicate that it is not derived from the vitreous or serum but instead is synthesized locally. The presence of IGF-I and IGF-BP in the IPM, together with the presence of IGF-I receptors on both photoreceptor and RPE cells, suggests the presence of an outer retina autocrine-paracrine system.

Animals↗