Biomedical subjects

E Rungger-Brändle

Publications and source records attributed to E Rungger-Brändle.

At least 19 recordsLinked to original sources

PubMed2004

Ultrastructural alterations in capillaries of the diabetic hypertensive rat retina: protective effects of ACE inhibition.

AIMS/HYPOTHESIS: The ACE inhibitor cilazapril was administered to diabetic hypertensive rats to evaluate its ability to influence the development of retinal capillary alterations. METHODS: Normotensive (strain: Wistar Kyoto) and genetically hypertensive (strain: spontaneously hypertensive) rats were rendered diabetic by intravenous injections of streptozotocin. Half of the diabetic animals received cilazapril with their daily food. At 20 weeks of diabetes, endothelial cells, pericytes and extracellular matrix were assessed by ultrastructural morphometry. Each experimental group consisted of seven animals. RESULTS: Cilazapril normalised systolic arterial pressure in diabetic hypertensive rats (137+/-2 mm Hg compared with 188+/-16 mm Hg in non-medicated diabetic hypertensive rats, p<0.001). The number of endothelial intercellular junctions was reduced in untreated diabetic hypertensive rats (0.15+/-0.05, p<0.02, vs 0.47+/-0.20 in non-diabetic normotensive rats). In diabetic hypertensive animals treated with cilazapril, this loss was attenuated (0.32+/-0.16, p<0.05). The significant thickening of the basement membrane observed in the diabetic normotensive (132.8+/-19.4 nm) and diabetic hypertensive (150.3+/-20.2 nm) groups was decreased by cilazapril in the diabetic hypertensive group (116.7+/-11.0 nm, p<0.01), but was unaffected in the normotensive (131.9+/-17.3 nm) group. No protective effect of the drug was observed in either group on pericytes. CONCLUSIONS/INTERPRETATION: Long-term administration of an effective antihypertensive therapy normalises endothelial alterations and basement membrane thickness in diabetic hypertensive conditions, and thus may account for the well-known improvement of the blood-retinal barrier observed during antihypertensive treatment.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2000

[Effect of insulin on retinal glycogen content].

BACKGROUND: The effect of insulin on glucose and glycogen metabolism in peripheral organs is well known. However, information about the action of this peptide in the retina is incomplete. We addressed the questions whether insulin influences glycogen content in the cat retina and whether glycogen breakdown is triggered by lack of glucose. MATERIAL AND METHODS: Eyes from adult cats were enucleated under deep barbiturate and fentanylanesthesia. Retinas were snap frozen either before or following arterial in vitro perfusion. Three conditions were studied: a) Perfusion with a glucose- and insulin-free medium; b) perfusion with the addition of physiologic glucose concentration; and c) in combination with insulin. Glycogen content was determined by in vitro measurement of glucose converted from glycogen. RESULTS: The reference value for retinal glycogen after enucleation (10 min of ischemia) is 2.4 micrograms glucose/mg protein. Glucose- and insulin-free perfusion for 80 min following "normoglycemia" reduced the amount of retinal glycogen by one third. Perfusion for 3 h with 5.5 mM glucose led to a small increase of the partly depleted glycogen stores. Insulin, in contrast, markedly augmented the glycogen content. CONCLUSIONS: Insulin led to an increase in retinal glycogen content, indicating an influence of this peptide on retinal glucose and glycogen metabolism. However, it appears that glycogen might play a dynamic role in retinal metabolism as a buffer between abrupt changes in focal metabolic demands that occur during normal glucose supply rather than acting solely as an emergency energy reserve for neural function during hypoglycemia.

Animals↗

PubMed2000

Glial reactivity, an early feature of diabetic retinopathy.

PURPOSE: To characterize early structural gliotic reactions in retinal Müller cells, astrocytes, and microglia in experimentally induced diabetes. METHODS: Rats were rendered diabetic by streptozotocin injection and killed after 2, 4, 12, or 20 weeks. Cell densities were determined in flatmounted retinas or transverse semithin sections. Expression of glial fibrillary acidic protein (GFAP) was localized on frozen sections or flatmounts by immunofluorescence and confocal microscopy, and GFAP content was evaluated by Western blot analysis. Microglial cells were visualized by binding of isolectin B4 or staining with antibodies to phosphotyrosine residues. The integrity of the blood-retinal barrier was assessed by intravenous injection of Evans blue. RESULTS: The density of Müller cells and microglia was significantly increased at 4 weeks of diabetes compared with nondiabetic controls. GFAP expression in Müller cells was not detected at 4 weeks but was prominent at 12 weeks. The number of astrocytes was significantly reduced at 4 weeks in the peripapillary and far peripheral retina. Shape changes of microglial cells indicated functional activation. Leakage of the blood-retinal barrier was observed at 2 weeks of hyperglycemia, the earliest time point investigated. CONCLUSIONS: The leakage of the blood-retinal barrier before glial reactivity suggests that glia are early targets of vascular hyperpermeability. The individual glial cell types react differentially to the diabetic state. Müller cells undergo hyperplasia preceding GFAP expression, and microglial cells are activated, whereas astrocytes regress. This glial behavior may contribute decisively to the onset and development of neuropathy in the diabetic retina.

Animals↗

PubMed1999

Remodeling of retinal capillaries in the diabetic hypertensive rat.

PURPOSE: To document the effect of sustained systemic hypertension on the integrity and ultrastructural morphology of retinal capillaries in diabetic and nondiabetic rats. METHODS: Normotensive (strain Wistar-Kyoto; WKY) and genetically hypertensive (spontaneously hypertensive; SHR) rats were rendered diabetic by intravenous streptozotocin injection. At 20 weeks of diabetes, endothelial cells, pericytes, and extracellular matrix were evaluated by ultrastructural morphometry. Serum albumin was localized by immunofluorescence microscopy. RESULTS: The endothelial cell layer was markedly thinner in the diabetic normotensive animals. The number of intercellular junctions was reduced in both the nondiabetic and diabetic hypertensive group but less so in the diabetic normotensive group. No significant endothelial cell loss was noted in either of the experimental groups, whereas the number of pericytes and the number of their cytoplasmic processes were reduced in diabetic and hypertensive animals. Significant thickening of the basement membrane and increased permeability to serum albumin were observed in diabetic and hypertensive rats and were strongly enhanced in the combined diseases. CONCLUSIONS: Endothelial thinning and shape changes from an elaborate to a simpler form as well as rounding up of the pericytes and loosening of their vascular sheaths indicate remodeling of the vascular wall during chronic diabetes and sustained hypertension, before a characteristic vasculopathy becomes manifest. The combination of diabetes and hypertension enhances these features, as well as basement membrane thickening and breakdown of the blood-retinal barrier.

Animals↗

PubMed1996

Differential regulation of Src-family protein tyrosine kinases in GPI domains of T lymphocyte plasma membranes.

The association of glycosylphosphatidylinositol (GPI)-anchored cell surface glycoproteins with Src-family protein tyrosine kinases was analysed in intact T lymphocyte plasma membranes. Following subcellular fractionation without detergent, 25% of the recovered plasma membranes were light density vesicles enriched in GPI-anchored glycoproteins and sphingolipids (GPI domains), while the remainder behaved as heavier density vesicles containing equal amounts of lipids and proteins. Qualitatively similar lipids were found in both vesicle types, but only light density vesicles made of 65-75% lipids yielded a Triton X-100 resistant, sedimentable fraction containing GPI-linked glycoproteins and sphingolipids. The GPI-rich vesicles phosphotyrosylated an exogenous substrate as efficiently as the denser vesicles, despite a low Lck and Fyn kinase content. Likewise, these kinases were more efficiently phosphorylated in GPI domains than in denser vesicles. GPI domains thus could constitute plasma membrane "hot spots" where associated Src kinases assume an optimally active conformation that contributes to signaling via GPI-anchored cell surface glycoproteins.

Animals↗

PubMed1996

Histochemical demonstration of glycogen in neurons of the cat retina.

PURPOSE: To demonstrate histochemically the cellular distribution of particulate glycogen in the cat retina and to correlate it with glucose sensitivity of neuronal electrical activities. METHODS: Free-floating, ultrathin sections of cat eyes (without glucose challenges) were stained by the periodic acid-thiocarbohydrazide-silver proteinate procedure and examined by electron microscopy. RESULTS: Muller cells were filled uniformly with fine-grain glycogen throughout all retinal layers. Particle density was higher in Muller cells of the peripheral retina than in those of central retina. Astrocytes contained little, if any, particulate glycogen. Alpha and beta ganglion cells had a heavy content of clumped glycogen granules. Rod bipolar and A17 amacrine cells of the rod pathway were stained intensely with particulate glycogen. No glycogen was seen in photoreceptor cells, cone bipolar cells, and the majority of amacrine cells, including AII cells of the rod pathway. However, one type of cone bipolar-driven amacrine cell was intensely glycogen positive. Its ultrastructural morphology, stratification pattern, and synaptology suggest that is a wide-field, axon-bearing type called A22. CONCLUSIONS: Except for the cone bipolar-driven ON-OFF A22 amacrine cell, it appears that glycogen staining preferentially labels neurons of the rod pathway. These observations are compatible with the reported sensitivity of the rod-driven electroretinogram and optic nerve response to glucose in the cat retina.

Animals↗

PubMed1996

Expression and release of tumor necrosis factor-alpha by explants of mouse cornea.

PURPOSE: To elucidate a possible target of immunosuppressive agents widely used in the treatment of corneal disorders, the authors determined whether corneal cells are capable of expressing and releasing tumor necrosis factor-alpha (TNF alpha) on lipopolysaccharide (LPS) stimulation, and they investigated whether TNF alpha production can be modulated by pharmacologic agents. METHODS: Trephined central corneas from C57BL/6 mice were kept in culture for 3 days. Release of TNF alpha after a 24-hour stimulation with LPS (1 microgram/ml) into the culture medium was determined both by bioassay and by enzyme-linked immunosorbent assay. Expression of TNF alpha mRNA after 6-hour stimulation was examined by polymerase chain reaction. Immunofluorescent staining on cryostat sections of cultured corneas was performed to localize TNF alpha in the tissue. Corneal explants were pretreated with immunosuppressive agents (prednisolone, budesonide, cyclosporin A) for 48 hours, followed by 6-or 24-hour stimulation with LPS in the continuous presence of the agents. RESULTS: Lipopolysaccharide stimulated TNF alpha release into the culture medium. The addition of budesonide (10(-7) M) or prednisolone (10(-6) M) significantly inhibited LPS-induced TNF alpha release, whereas cyclosporin A (10(-7) - 10(-5) M) had no marked effect. Levels of TNF alpha mRNA in corneal explants increased fivefold after stimulation with LPS. Immunohistochemical staining revealed that TNF alpha was expressed in the epithelial cells. Budesonide markedly decreased mRNA expression and abolished immunostaining of TNF alpha stimulated by LPS. CONCLUSIONS: TNF alpha is produced and released by the epithelial cells of mouse central cornea in response to LPS. Contrary to cyclosporin A, corticosteroids such as prednisolone and budesonide potently inhibit TNF alpha production.

Animals↗

PubMed1995

Behaviour of macroglial cells, as identified by their intermediate filament complement, during optic nerve regeneration of Xenopus tadpole.

Assessment of glial cell behaviour during optic nerve (ON) regeneration in Xenopus tadpoles is hampered by the lack of classical cellular markers that distinguish different glial cells in mammals. We thus have characterized the intermediate filament (IF) complement of tadpole glial cells and used it to follow the fate of glial cell subsets during the first 10 days after ON crush. Glial cells synthesize a restricted number of cytokeratin (CK) species and vimentin. This pattern remains essentially unchanged during metamorphosis and regeneration. However, vimentin turnover is specifically enhanced after injury. The expression of CKs and vimentin has been followed immunocytochemically in situ and in isolated cells recovered from dissociated ON segments. In the normal nerve, 79% of ramified glial cells express both CK and vimentin, 1% CK and 4% vimentin only, whereas 16% express neither IF protein. We tentatively classified CK expressing cells as mature astrocytes and those without IF proteins as oligodendrocytes. In the regenerating ON, the relative number of oligodendrocytes is decreased, while the astrocytic subset becomes accordingly larger but is decreased by day 10 already in favour of cells expressing vimentin only. Astrocytes invade the lesion site soon after crush, arrange into a central core within the distal nerve segment and establish a peripheral scaffold that is readily crossed by axons. Unlike mammalian astrocytes that remain absent from the lesion site but form a scar at some distance to it, amphibian astrocytes appear to provide active guidance to axons growing through the lesion site.

Animals↗

PubMed1995

Inhibition of Xhox1A gene expression in Xenopus embryos by antisense RNA produced from an expression vector read by RNA polymerase III.

Antisense inhibition of gene expression during Xenopus development was obtained by injecting, into the zygote, an expression vector carrying the adenovirus VAI gene read by RNA polymerase III. This vector yields high levels of antisense RNA in most embryonic cells between mid-blastula transition and tailbud stage. As a target we chose the Xenopus homeobox gene Xhox1A. A 26 bp long oligonucleotide, including the initiation codon of this gene, was inserted in opposite polarity into the vector. Antisense treatment reduces Xhox1A mRNA in embryos up to stage 22 and Xhox1A protein expression up to stage 30. Half of the antisense-treated embryos develop a characteristic phenotype with disorganized somites in the anterior trunk and delayed development of the intestinal tract.

Animals↗

PubMed1994

Effect of disruption of actin filaments by Clostridium botulinum C2 toxin on insulin secretion in HIT-T15 cells and pancreatic islets.

To examine their role in insulin secretion, actin filaments (AFs) were disrupted by Clostridium botulinum C2 toxin that ADP-ribosylates G-actin. Ribosylation also prevents polymerization of G-actin to F-actin and inhibits AF assembly by capping the fast-growing end of F-actin. Pretreatment of HIT-T15 cells with the toxin inhibited stimulated insulin secretion in a time- and dose-dependent manner. The toxin did not affect cellular insulin content or nonstimulated secretion. In static incubation, toxin treatment caused 45-50% inhibition of secretion induced by nutrients alone (10 mM glucose + 5 mM glutamine + 5 mM leucine) or combined with bombesin (phospholipase C-activator) and 20% reduction of that potentiated by forskolin (stimulator of adenylyl cyclase). In perifusion, the stimulated secretion during the first phase was marginally diminished, whereas the second phase was inhibited by approximately 80%. Pretreatment of HIT cells with wartmannin, a myosin light chain kinase inhibitor, caused a similar pattern of inhibition of the biphasic insulin release as C2 toxin. Nutrient metabolism and bombesin-evoked rise in cytosolic free Ca2+ were not affected by C2 toxin, indicating that nutrient recognition and the coupling between receptor activation and second messenger generation was not changed. In the toxin-treated cells, the AF web beneath the plasma membrane and the diffuse cytoplasmic F-actin fibers disappeared, as shown both by staining with an antibody against G- and F-actin and by staining F-actin with fluorescent phallacidin. C2 toxin dose-dependently reduced cellular F-actin content. Stimulation of insulin secretion was not associated with changes in F-actin content and organization. Treatment of cells with cytochalasin E and B, which shorten AFs, inhibited the stimulated insulin release by 30-50% although differing in their effects on F-actin content. In contrast to HIT-T15 cells, insulin secretion was potentiated in isolated rat islets after disruption of microfilaments with C2 toxin, most notably during the first phase. This effect was, however, diminished, and the second phase became slightly inhibited when the islets were degranulated. These results indicate an important role for AFs in insulin secretion. In the poorly granulated HIT-T15 cells actin-myosin interactions may participate in the recruitment of secretory granules to the releasable pool. In native islet beta-cells the predominant function of AFs appears to be the limitation of the access of granules to the plasma membrane.

Actin Cytoskeleton↗

PubMed1993

Confocal microscopy and computer-assisted image reconstruction of astrocytes in the mammalian retina.

The distribution of astrocytes in the vascularized retina of pigs, rats and cats was investigated by confocal microscopy and computer-assisted image processing. In whole mounts, immunocytochemical identification was done by staining astrocytes for glial fibrillary acidic protein (GFAP), and blood vessels for alpha-smooth muscle actin or collagen IV. Double-staining was followed through consecutive optical sections and made it possible to precisely align the two markers in the inner retina. The resulting computer-assisted image reconstructions revealed asymmetric ensheathment of blood vessels by GFAP-positive fibres. The ultrastructural basis for this asymmetry, as studied by electron microscopy, was found to be different in pigs and cats. In the pig, astrocytes firmly ensheathed the vessel circumference, but glial filaments were much more abundant on the vitreal and lateral than on the scleral side. By contrast, in the cat astrocytes were generally confined to regions occupied by axonal bundles and constituted only part of the vascular glia limitans, else formed by Müller cells. Moreover, our observations unambiguously showed that individual astrocytes maintained simultaneous contact with axons and blood vessels and lined the vitreous body. The physical links provided by astrocytes suggest that they are able to function as central communicating elements between ganglion cells, the vasculature and the vitreous body.

Animals↗

PubMed1993

Three-dimensional visualization of multi-channel volume data: the amSFP algorithm.

In this paper we present a three-dimensional visualization technique for multi-channel volume data. The technique simulates the physical process of fluorescence, hence its name: achromatic multi-channel simulated fluorescent process (amSFP). The data set is simulated as 3D distribution of different fluorescent dyes, where each channel is represented by a particular type of dye. Apart from the spatial density map, no additional characteristics about the data set have to be defined; no image segmentation is needed prior to visualization. The degree of interaction among the channels in the fluorescence process can be adapted to optimally render specific structures in the image. 3D multi-channel data can be obtained by a three-dimensional imaging device that is able to measure a number of physical quantities at a given location within a specimen. The fluorescence principle, the algorithm, and its implementation are presented. We have used the technique to investigate the relative spatial arrangement of blood vessels and astrocytes in the cat retina. The two components have been stained with different fluorescence dyes and recorded in a confocal light microscope to form a two-channel 3D data set.

Algorithms↗

PubMed1990

Isolation of high-affinity murine interleukin 2 receptors as detergent-resistant membrane complexes.

Murine T cells and T cell lines bearing high- and low-affinity receptors for interleukin (IL) 2 were chemically cross-linked to radiolabeled IL 2 and subjected to differential detergent extractions to evaluate the extent of IL 2 receptor association with the nonionic detergent-resistant framework of the plasma membrane. Low-affinity receptors were readily solubilized by nonionic detergent extraction of whole cross-linked cells, while solubilization of high-affinity receptors required a stronger ionic detergent suggesting their association with a membrane structure that is resistant to nonionic detergents. To achieve physical separation of low- and high-affinity receptors, cells cross-linked to 125I-labeled IL 2 were centrifuged through a sucrose barrier containing Triton X-100. Alternatively, Triton X-114 extracts of plasma membrane fractions were partitioned into aqueous and detergent phases. By either approach, high-affinity receptors differed from low-affinity ones by their increased density and consisted of detergent-resistant complexes containing p55-p75 heterodimers. The low-affinity receptors, on the contrary, were of low density and consisted exclusively of detergent-soluble p55 subunits. High density and resistance to nonionic detergent extraction of high-affinity IL 2 receptors suggest their integration into lateral microdomains of the detergent-resistant framework of the plasma membrane.

Animals↗

PubMed1990

Ocular complications in the old and glucose-intolerant genetically obese (fa/fa) rat.

Genetically obese fatty (fa/fa) male rats with abnormal oral glucose tolerance associated with initial hyperinsulinaemia as well as control lean (FA/FA) rats were investigated for the development of retinal microangiopathies. The animals were kept on a standard or sucrose supplemented diet. When tested at 60 weeks, the glucose intolerance of fa/fa rats was accompanied by an insulin response that was now either comparable to that of lean rats (standard diet) or close to nil (sucrose supplemented diet). At killing (68 weeks of age), retinal vasculature was examined by electron microscopy and morphological changes were quantitatively assessed by ultrastructural morphometry. A retinal microangiopathy was observed in all mutant animals which was more pronounced in the sucrose fed group, and which was characterized by: (1), an increase in focal thickenings and in nodules of the basement membrane adjacent to the perivascular glial cells: (2), a decrease in the number of pericyte nulei with concomitant signs of early degenerative cytoplasmic changes of pericytes; (3), an increase in the pinocytic activity of endothelial cells, indicative of presumptive changes in vascular permeability; (4), an increase in the number of intercellular endothelial junctions; (5), the presence of numerous stimulated platelets within capillaries. The fa/fa rat may thus be considered as a suitable model for studying the pathophysiology of ocular complications, in particular retinopathy accompanying non-insulin-dependent diabetes.

Animals↗

PubMed1989

An epithelium-type cytoskeleton in a glial cell: astrocytes of amphibian optic nerves contain cytokeratin filaments and are connected by desmosomes.

In higher vertebrates the cytoskeleton of glial cells, notably astrocytes, is characterized (a) by masses of intermediate filaments (IFs) that contain the hallmark protein of glial differentiation, the glial filament protein (GFP); and (b) by the absence of cytokeratin IFs and IF-anchoring membrane domains of the desmosome type. Here we report that in certain amphibian species (Xenopus laevis, Rana ridibunda, and Pleurodeles waltlii) the astrocytes of the optic nerve contain a completely different type of cytoskeleton. In immunofluorescence microscopy using antibodies specific for different IF and desmosomal proteins, the astrocytes of this nerve are positive for cytokeratins and desmoplakins; by electron microscopy these reactions could be correlated to IF bundles and desmosomes. By gel electrophoresis of cytoskeletal proteins, combined with immunoblotting, we demonstrate the cytokeratinous nature of the major IF proteins of these astroglial cells, comprising at least three major cytokeratins. In this tissue we have not detected a major IF protein that could correspond to GFP. In contrast, cytokeratin IFs and desmosomes have not been detected in the glial cells of brain and spinal cord or in certain peripheral nerves, such as the sciatic nerve. These results provide an example of the formation of a cytokeratin cytoskeleton in the context of a nonepithelial differentiation program. They further show that glial differentiation and functions, commonly correlated with the formation of GFP filaments, are not necessarily dependent on GFP but can also be achieved with structures typical of epithelial differentiation; i.e., cytokeratin IFs and desmosomes. We discuss the cytoskeletal differences of glial cells in different kinds of nerves in the same animal, with special emphasis on the optic nerve of lower vertebrates as a widely studied model system of glial development and nerve regeneration.

Animals↗

PubMed1989

Cytokeratin filaments and desmosomes in the epithelioid cells of the perineurial and arachnoidal sheaths of some vertebrate species.

Using electron microscopy and immunohistochemistry with a large panel of antibodies to various cytoskeletal proteins we have noted that the single- or multi-layered sheaths of epithelioid cells ("neurothelia") surrounding peripheral nerves (perineurial cells) or structures of the central nervous system, including the optic nerve (arachnoid cells), show remarkable interspecies differences in their cytoskeletal complements. In two anuran amphibia examined (Xenopus laevis, Rana ridibunda), the cells of both forms of neurothelia, i.e., perineurial and arachnoid, are interconnected by true desmosomes and are rich intermediate-sized filaments (IFs) of the cytokeratin type. Among higher vertebrates, a similar situation is found in the bovine and chicken nervous systems, in which the arachnoid cells of the meninges contain desmosomes and IFs of both the cytokeratin (apparently with restricted epitope accessibilities in the chicken) and the vimentin type, whereas the perineurial cells of many nerves contain cytokeratin IFs, often together with vimentin, but no desmosomes. In contrast, in rat arachnoidal and perineurial cells significant reactions have been observed neither for cytokeratins nor for desmosomes. In the human nervous system, cytokeratins and desmosomes have also not been seen in the various perineuria studied whereas desmosomes are frequent in arachnoidal cell layers which are dominated by vimentin IFs and only in certain small regions of the brain contain some additional cytokeratins. The occurrence of cytokeratins in the tissues found positive by immunohistochemistry has been confirmed by gel electrophoresis of cytoskeletal proteins, followed by immunoblotting. Our results emphasize both similarities and differences between the neurothelia on the one hand and epithelia or endothelia on the other, justifying classification as a separate kind of tissue, i.e., neurothelium. The observations of interspecies differences lead to the challenging conclusion that neither desmosomes nor cytokeratins are essential for the basic functions of neurothelial sheaths nor does the specific type of IF protein expressed in these cells appear to matter in this respect. The results are also discussed in relation to the cytoskeletal characteristics of other epithelioid tissues and of human neurothelium-derived tumors.

Animals↗

PubMed1988

Cytoskeletons of retinal pigment epithelial cells: interspecies differences of expression patterns indicate independence of cell function from the specific complement of cytoskeletal proteins.

In vertebrate tissue development a given cell differentiation pathway is usually associated with a pattern of expression of a specific set of cytoskeletal proteins, including different intermediate filament (IF) and junctional proteins, which is identical in diverse species. The retinal pigment epithelium (RPE) is a layer of polar cells that have very similar morphological features and practically identical functions in different vertebrate species. However, in biochemical and immunolocalization studies of the cytoskeletal proteins of these cells we have noted remarkable interspecies differences. While chicken RPE cells contain only IFs of the vimentin type and do not possess desmosomes and desmosomal proteins RPE cells of diverse amphibian (Rana ridibunda, Xenopus laevis) and mammalian (rat, guinea pig, rabbit, cow, human) species express cytokeratins 8 and 18 either as their sole IF proteins, or together with vimentin IFs as in guinea pig and a certain subpopulation of bovine RPE cells. Plakoglobin, a plaque protein common to desmosomes and the zonula adhaerens exists in RPE cells of all species, whereas desmoplakin and desmoglein have been identified only in RPE desmosomes of frogs and cows, including bovine RPE cell cultures in which cytokeratins have disappeared and vimentin IFs are the only IFs present. These challenging findings show that neither cytokeratin IFs nor desmosomes are necessary for the establishment and function of a polar epithelial cell layer and that the same basic cellular architecture can be achieved by different programs of expression of cytoskeletal proteins. The differences in the composition of the RPE cytoskeleton further indicate that, at least in this tissue, a specific program of expression of IF and desmosomal proteins is not related to the functions of the RPE cell, which are very similar in the various species.

Animals↗

PubMed1987

Exocytic clearing of degraded membrane material from pigment epithelial cells in frog retina.

Posterior eye cups of the frog Rana ridibunda were prefixed in the presence of tannic acid, osmicated and stained en bloc with uranyl acetate. Electron microscopy revealed the following features of membrane traffic in cells of the retinal pigment epithelium (RPE): (1) intracellular membranes with increased electron density undergo degradation within phagolysosomes and also outside lysosomes and are committed to be exocytized; (2) exocytized degraded membranes, organized as lamellar arrays, are evacuated through the basolateral extracellular space, through Bruch's membrane and into the choriocapillaris. Comparison of exocytic activity in animals kept either with a light cycle or in constant darkness suggests that exocytized lamellar arrays derive from membranes degraded through both lysosomal and non-lysosomal pathways. Autophagocytosis may contribute a substantial amount of material to exocytosis. On the other hand, exocytosis of heterophagosomes, if it takes place at all, involves only residual bodies at a final stage of degradation following slow proteolysis which is achieved within the RPE cells. Rapid transcytosis of heterophagosomes does not occur. Taken together, our observations suggest that, in the frog, exocytosis and subsequent evacuation of residual bodies is an efficient mechanism for clearing from worn-out organelles the metabolically highly active, non-dividing RPE cells.

Animals↗