Biomedical subjects

Andreas Reichenbach

Publications and source records attributed to Andreas Reichenbach.

At least 37 records · Page 2Linked to original sources

PubMed2005

Protective effects of various antioxidants during ischemia-reperfusion in the rat retina.

BACKGROUND: Oxidative stress during ischemia-reperfusion (I/R) is thought to be a major cause of retinal injury after I/R. The present study was aimed at investigating the protective role of antioxidant application. METHODS: Four commonly used antioxidants (vitamin E=alpha tocopherol, lutein, fenugreek=Trigonella foenum-graecum and germander=Teucrium multicaule) were applied in ischemia-reperfusion (I/R) injury of the right retinae of 51 adult pigmented rats. Each of the antioxidants was administered every 6 h, beginning 6 h before the ischemia. After 60 min ischemia and 24 h reperfusion, we assayed (1) oxidative damage by measuring malondialdehyde (MDA), (2) apoptosis by measuring activated caspase-3 (using immunoblots), and (3) intrinsic antioxidative capacity by measuring glutathione (GSH) levels in the retinae. RESULTS: In the order of lutein>Trigonella>vitamin E>Teucrium, all four compounds were effective in preventing retinal damage by I/R, as (1) they significantly decreased the formation of MDA (8.83, 16.48, 17.24, 18.5 nmol/100 mg tissue wet weight, respectively) compared with I/R without protection (23.29 nmol/100 mg tissue wet weight; controls: 8.0 nmol/100 mg tissue wet weight); (2) they significantly inhibited the activation of caspase-3 [0.01, 0.02, 0,02, and 0.04 arbitrary units (AU), respectively, versus control, 0.0, and I/R, 0.08 AU]; and (3) they significantly decelerated the loss of GSH (from control levels of 36.04 nmol/100 mg tissue wet weight) to 30.4, 15.98, 18.1, 15.02 nmol/100 mg tissue wet weight, respectively (lutein, Trigonella, vitamin E, Teucrium), compared with unprotected I/R (12.84 nmol/100 mg tissue wet weight). CONCLUSIONS: Our study shows that lutein, Trigonella, Teucrium and vitamin E exert protection against in vivo retinal I/R injury in rats; this may recommend these compounds (in particular, lutein) for clinical use in patients with different types of ocular I/R injuries.

Animals↗

PubMed2005

Atypical gliosis in Müller cells of the slowly degenerating rds mutant mouse retina.

Retinal Müller glial cells are known to undergo reactive changes (gliosis) in various retinal diseases. In virtually all cases studied, an upregulation of glial fibrillary acidic protein (GFAP) and a hypertrophy can be observed. Physiological alterations, such as a strong downregulation of inwardly rectifying K+ (Kir) currents, were found after retinal detachment (man, rabbit) and after ischemia/reperfusion (rat) but not in more slowly progressing retinal degenerations (Borna Disease Virus-infected rats, RCS rats). This led us to hypothesize that Müller cells respond with 'typical' reactive gliosis only to rapid but not to slow retinal degeneration. To test this hypothesis, we studied Müller cells from rds mutant mice (PrphRd2), which show a retinal degeneration of early onset and slow progression, resulting in a complete loss of photoreceptors after 9-12 months. In Müller cells of rds mice, we found immunoreactivity for GFAP, a marker of gliosis in Müller cells, from postnatal day 21 on, accompanied by a moderately increased membrane capacitance (taken as an indicator of hypertrophy), whereas no change in the expression of the Kir4.1 protein occurred in adult rds mice. We failed to observe significant changes in the membrane resistance and the membrane potential of cells from rds mice from first week after birth until 1 year of age. Current densities were decreased in cells from 3- and 5-week old rds mice. Furthermore, as in control cells from wildtype animals, these cells displayed dominant Kir currents, voltage-dependent Na+ currents, and glutamate uptake currents. These data support the idea that in mice as well as previously shown in rats, slow retinal degeneration induces an atypical gliosis of Müller cells.

Animals↗

PubMed2005

The glucocorticoid triamcinolone acetonide inhibits osmotic swelling of retinal glial cells via stimulation of endogenous adenosine signaling.

The glucocorticoid triamcinolone acetonide is clinically used for the treatment of macular edema. However, the edema-resolving mechanisms of triamcinolone are incompletely understood. Since cell swelling is a central cause of cytotoxic edema in the brain and retina, we determined the effects of triamcinolone acetonide on the swelling of retinal ganglion and Müller glial cells in acutely isolated retinas from rats and guinea pigs in situ. Triamcinolone acetonide (100 microM) had no effect on the swelling of ganglion cells that was evoked in isolated whole mounts of the guinea pig retina by acute application of glutamate (1 mM) or high K+ (50 mM). However, triamcinolone reversed the osmotic swelling of Müller glial cells in retinas of the rat that was observed under various experimental conditions: in retinas isolated at 3 days after transient retinal ischemia, in retinas of eyes with lipopolysaccharide-induced ocular inflammation, and in control retinas in the presence of Ba2+ (1 mM), H2O2 (200 microM), arachidonic acid (10 microM), or prostaglandin E2 (30 nM). The inhibiting effect of triamcinolone on osmotic glial cell swelling was mediated by stimulation of transporter-mediated release of endogenous adenosine and subsequent A1 receptor activation, resulting in an elevation of the intracellular cAMP level and activation of the protein kinase A, and, finally, in an opening of extrusion pathways for K+ and Cl- ions. The inhibitory effect on the cytotoxic swelling of glial cells may contribute to the fast edema-resolving effect of vitreal triamcinolone observed in human patients.

Adenosine↗

PubMed2005

Changes in retinal gene expression in proliferative vitreoretinopathy: glial cell expression of HB-EGF.

PURPOSE: To compare the gene expression pattern of control postmortem retinas with retinas from patients with proliferative vitreoretinopathy (PVR), to determine the expression of the heparin binding epidermal growth factor-like growth factor (HB-EGF) by glial cells in fibroproliferative membranes, and to examine whether cells of the human Müller cell line, MIO-M1, respond to HB-EGF with proliferation, migration, and secretion of the vascular endothelial growth factor (VEGF). METHODS: To identify genes that were differently expressed in PVR and control retinas, the RNA from the neural retinas of seven postmortem donors and of two patients with PVR were analyzed for differential gene expression, by hybridization of labeled cRNA probes to an Affymetrix human genome microarray set. The results were validated by real time PCR experiments investigating RNA from 6 postmortem retinas and 4 PVR retinas. Epiretinal PVR membranes were immunohistochemically stained for colocalization of HB-EGF and the glial cell marker, glial fibrillary acidic protein (GFAP). The HB-EGF evoked proliferation of cultured Müller cells was investigated by a bromodeoxyuridine immunoassay, chemotaxis was assessed with a migration assay, and the release of VEGF was evaluated by ELISA. RESULTS: Out of the 12,600 genes and expressed sequence tags investigated, the levels of 80 showed an increased expression, and 21 were expressed at decreased levels, in the retinas of PVR patients compared to the control retinas. The upregulated signals include genes for nuclear and cell cycle related proteins, extracellular secretory proteins, cytosolic signaling proteins, and proteins of the membrane and the extracellular matrix. The genes of the hepatocyte growth factor and of HB-EGF were found to be expressed in PVR retinas but not in control retinas. In epiretinal membranes of patients with PVR, HB-EGF immunoreactivity partially colocalized with GFAP. In cultured Müller cells, HB-EGF stimulated both proliferation and chemotaxis, and the secretion of VEGF, via activation of the extracellular signal regulated kinases 1 and 2 and of the phosphatidylinositol-3 kinase. CONCLUSIONS: The development of PVR is accompanied by complex changes of the gene expression in the neural retina, with an upregulation of genes that support cell proliferation, cell signaling, cell motility, and extracellular matrix remodeling. HB-EGF is one of the factors that are significantly upregulated in PVR retinas. HB-EGF expression in fibroproliferative tissue and its stimulatory effect on glial cell proliferation, chemotaxis, and VEGF secretion suggest that HB-EGF may be a factor mediating glial cell responses during PVR.

Adolescent↗

PubMed2005

Effect of alpha2-macroglobulin on retinal glial cell proliferation.

BACKGROUND: Activation of the receptor for alpha2-macroglobulin (alpha2 M), the low-density lipoprotein-related protein (LRP1; CD91), has been suggested to represent a possible strategy for the inhibition of uncontrolled retinal cell proliferation via stimulation of the clearance of alpha2 M-bound growth factors and proteinases from the extracellular space. In order to prove this assumption, we investigated the effect of alpha2 M on the proliferation of Müller glial cells in vitro. METHODS: Proliferation assays using bromodeoxyuridine were carried out on cultured Müller glial cells of the guinea pig in the absence and presence of alpha2 M. RESULTS: Activated alpha2 M evoked a slight increase of the cell proliferation at control conditions. Addition of alpha2 M to the culture medium inhibited the proliferation evoked by agonists of G-protein-coupled receptors [adenosine 5'-triphosphate (ATP), neuropeptide Y]. However, alpha2 M did not diminish the proliferation evoked by agonists of receptor tyrosine kinases (epidermal and platelet-derived growth factors) and by serum, respectively. Inhibition of LRP1 by a neutralizing antibody did not alter the ATP-evoked proliferation while it increased the proliferation in the presence of alpha2 M. CONCLUSION: It is concluded that alpha2 M inhibits the proliferation evoked by agonists of G-protein-coupled receptors, possibly via enhanced growth factor clearance by LRP.

Adenosine Triphosphate↗

PubMed2005

Glial cell-mediated spread of retinal degeneration during detachment: a hypothesis based upon studies in rabbits.

In human subjects with peripheral retinal detachments, visual deficits are not restricted to the detached retina but are also present in the non-detached tissue. Based upon studies on a rabbit model of rhegmatogenous retinal detachment, we propose a glial cell-mediated mechanism of spread of retinal degeneration into non-detached retinal areas which may also have importance for the understanding of alterations in the human retina. Both detached and attached portions of the rabbit retina display photoreceptor cell degeneration and cystic degeneration of the innermost layers. An inverse mode of photoreceptor cell degeneration in the attached tissue suggests a disturbed support of the photoreceptor cells by Müller cells which show various indications of gliosis (increased expression of intermediate filaments, cell hypertrophy, decreased plasma membrane K(+) conductance, increased Ca(2+) responsiveness to purinergic stimulation) in both detached and attached tissues. We propose that gliotic alterations of Müller cells contribute to the degeneration of the attached retina, via disturbance of glial homeostasis mechanisms. A down-regulation of the K(+) conductance of Müller cells may prevent effective retinal K(+) and water clearance, and may favor photoreceptor cell degeneration and edema development.

Adenosine Triphosphate↗

PubMed2005

Altered membrane physiology in Müller glial cells after transient ischemia of the rat retina.

Inwardly rectifying K+ (Kir) channels have been implicated in the mediation of retinal K+ homeostasis by Muller glial cells. To assess possible involvement of altered glial K+ channel expression in ischemia-reperfusion injury, transient retinal ischemia was induced in rat eyes. Acutely isolated Muller cells from postischemic retinae displayed a fast downregulation of their Kir currents, which began within 1 day and reached a maximum at 3 days of reperfusion, with a peak decrease to 20% as compared with control. This strong decrease of Kir currents was accompanied by an increase of the incidence of cells which displayed depolarization-evoked fast transient (A-type) K+ currents. While no cell from untreated control rats expressed A-type K+ currents, all cells investigated from 3- and 7-day postischemic retinae displayed such currents. An increased incidence of cells displaying fast transient Na+ currents was observed at 7 days after ischemia. These results suggest a role of altered glial Kir channel expression in postischemic neuronal degeneration via disturbance of retinal K+ siphoning.

Animals↗

PubMed2005

Glutamate transport by retinal Muller cells in glutamate/aspartate transporter-knockout mice.

Glutamate transporters are involved in maintaining extracellular glutamate at a low level to ensure a high signal-to-noise ratio for glutamatergic neurotransmission and to protect neurons from excitotoxic damage. The mammalian retina is known to express the excitatory amino acid transporters, EAAT1-5; however, their specific role in glutamate homeostasis is poorly understood. To examine the role of the glial glutamate/aspartate transporter (GLAST) in the retina, we have studied glutamate transport by Muller cells in GLAST-/- mice, using biochemical, electrophysiological, and immunocytochemical techniques. Glutamate uptake assays indicated that the Km value for glutamate uptake was similar in wild-type and GLAST-/- mouse retinas, but the Vmax was approximately 50% lower in the mutant. In Na+-free medium, the Vmax was further reduced by 40%. In patch-clamp recordings of dissociated Muller cells from GLAST-/- mice, application of 0.1 mM glutamate evoked no current showing that the cells lacked functional electrogenic glutamate transporters. The result also indicated that there was no compensatory upregulation of EAATs in Muller cells. [3H]D-Aspartate uptake autoradiography, however, showed that Na+-dependent, high-affinity transporters account for most of the glutamate uptake by Muller cells, and that Na+-independent glutamate transport is negligible. Additional experiments showed that the residual glutamate uptake in Muller cells in the GLAST-/- mouse retina is not due to known glutamate transporters-cystine-glutamate exchanger, ASCT-1, AGT-1, or other heteroexchangers. The present study shows that while several known glutamate transporters are expressed by mammalian Muller cells, new Na+-dependent, high-affinity glutamate transporters remain to be identified.

Amino Acid Transport System ASC↗

PubMed2005

Membrane-associated guanylate kinase proteins MPP4 and MPP5 associate with Veli3 at distinct intercellular junctions of the neurosensory retina.

MPP4 and MPP5 are closely related members of the p55-subfamily of membrane-associated guanylate kinases (MAGUKs) known to mediate the assembly of protein complexes at the plasma membrane of cell-cell junctions. Both MPP4 and MPP5 have been implicated in retinal function; however, their specific roles in the cellular mechanisms underlying vision are largely unknown. Here, we generated specific poly- and monoclonal antibodies against the two proteins and show that MPP4 and MPP5 are localized at distinct sites of cell-cell contact in the mouse retina. While MPP4 is a component of the synaptic terminals of photoreceptors, MPP5 exclusively localizes to apical membrane domains of the outer limiting membrane (OLM) junctions. The vertebrate homologs of Caenorhabditis elegans lin-7, Veli1, -2, and -3, have previously been identified as putative binding partners of MPP5. In this study, we show that MPP4 directly interacts with the Veli proteins via L27 heterodimerization in vitro. In addition, two of the three Veli isoforms, Veli1 and -3, are demonstrated to be expressed in the mouse retina. Immunofluorescence microscopy reveals extensive colocalization of Veli3 with both MPP4 and MPP5. This association of Veli3 with either MPP4 or MPP5 suggests that the MAGUKs recruit Veli3 and its binding partners to different cellular regions of the retina where they may participate in the organization of specialized intercellular junctions.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Glycogen phosphorylase isozyme pattern in mammalian retinal Müller (glial) cells and in astrocytes of retina and optic nerve.

Müller cells, the radially oriented dominant macroglial cells of the retina, are known to contain abundant glycogen as well as the key enzyme for its degradation, glycogen phosphorylase (GP), but the expressed isozyme pattern is unknown. To elucidate the isoform expression pattern, specific antisera directed against the brain (BB) and muscle (MM) isoforms of GP were applied to retinal sections, isolated Müller cells, and sections of the optic nerve. We show that Müller cells of rat, rabbit, guinea pig, and mouse retina exclusively express the BB isoform. Astrocytes of rat and rabbit optic nerve, as well as retina express only the BB isoform. In contrast, astrocytes in the brain and spinal cord as well as the epithelial cells of the pars caeca and of the ciliary body express both the BB and MM isoform. This result may indicate some differences in the role of glycogen in retinal macroglia and brain astrocytes, reflecting a local specialization of macroglia in the retina proper.

Animals↗

PubMed2005

The activation of IL-8 receptors in cultured guinea pig Müller glial cells is modified by signals from retinal pigment epithelium.

Interleukin 8 (IL-8, CXCL8) is a pro-inflammatory chemokine which attracts neutrophils to sites of inflammation via an activation of the G-protein-coupled receptors, CXCR1 and CXCR2. However, both IL-8 and IL-8 receptors are widely expressed in various tissues and cell types, and have been suggested to be involved in other functions such as angiogenesis, tumor growth, or brain pathology. We examined the expression of IL-8 and IL-8 receptors in highly enriched primary cultures of guinea pig Muller glial cells. Immunoreactivity for CXCL8, CXCR1 and CXCR2 was observed in all cultured Muller cells. The expression of CXCL8 was confirmed by PCR, and the secretion of the CXCL8 protein from Muller cells was revealed by ELISA. Western blots showed prominent bands at approximately 40 kDa by using antibodies specific for human CXCR1 and CXCR2, and the expression of a putative CXCR2 receptor in Muller cells was confirmed by PCR. Furthermore, cultured Muller cells responded to application of recombinant human IL-8 with an increase of the cytosolic Ca(2+) concentration. If supernatants of cultured human retinal pigment epithelium (RPE) cells were applied to the Muller cell cultures, no obvious changes were observed in the CXCL8, CXCR1 and CXCR2 expression but (i) Muller cell proliferation was stimulated, and (ii) there was an increased number of CXCL8-responsive Muller cells and the amplitudes of the evoked calcium responses were enhanced. It is concluded that Muller glial cells may participate in the inflammatory response(s) of the retina during ocular diseases, and that this contribution may be modified by interactions with RPE cells.

Adenosine Triphosphate↗

PubMed2005

Ocular inflammation alters swelling and membrane characteristics of rat Müller glial cells.

Ocular inflammation is a common cause of retinal edema that may involve swelling of Müller glial cells. In order to investigate whether endotoxin-induced ocular inflammation in rats alters the swelling and membrane characteristics of Müller cells, lipopolysaccharide (LPS; 0.5%) was intravitreally injected. At 3 and 7 days after treatment, hypotonic challenge induced swelling of Müller cell somata that was not observed in non-treated control eyes. Müller cells of LPS-treated eyes displayed a downregulation of inward K(+) currents and upregulation of A-type K(+) currents that was associated with a decreased expression of Kir4.1 protein in retinal slices. The data suggest that ocular inflammation induces alterations of both the swelling characteristics and the K(+) channel expression of Müller cells.

Analysis of Variance↗

PubMed2005

P2X(7) receptor-mRNA and -protein in the mouse retina; changes during retinal degeneration in BALBCrds mice.

A combined real-time PCR/immunohistochemistry study was carried out to investigate whether P2X(7) receptors, known to induce apoptosis and necrosis, may be causally related to the process of retinal degeneration in BALBCrds mice. In the retinae of BALBCrds mice, P2X(7) receptor-mRNA was the highest at an age of 20-40 days, and declined afterwards. At the same time, the P2X(7) receptor-message was constantly low in the retina of control BALBC mice until postnatal day 100. The receptor-mRNA in total brain tissue of both strains of mice was comparable with that of BALBCrds retinae. Double immunofluorescence in combination with laser scanning microscopy was used to study the distribution of P2X(7) receptor-immunoreactivity (IR) on neurons and different glial cell types of the retina. An exclusively neuronal localization of P2X(7)-IR in the ganglion cell layer was found by using either anti-neuronal nuclei or microtubule associated protein-2 as neuronal markers. There was a slight age-dependent decrease in the abundance of neuronal P2X(7)-IR both in BALBCrds or BALBC mice. P2X(7)-IR failed to co-localize with any of the non-neuronal markers used to stain microglial or Müller glial cells. No P2X(7) receptor-IR was found in the retinal ganglion cell layer of P2X(7)(-/-) animals, when compared with the control littermates. Hence, we suggest that, in BALBCrds mice, an early up-regulation of neuronal P2X(7) receptors may cause injury of retinal neurons and thereby functionally contribute to the retinal damage.

Aging↗

PubMed2005

Physiological properties of retinal Muller glial cells from the cynomolgus monkey, Macaca fascicularis--a comparison to human Muller cells.

Retinae from rabbits and laboratory rodents are often used as 'models' of the human retina, although there are anatomical differences. To test whether monkey eyes provide a better model, a physiological study of Muller glial cells was performed comparing isolated cells and retinal wholemounts from the cynomolgus monkey, Macaca fascicularis and from man. The membrane conductance of Muller cells from both species was dominated by inward and outward K(+) currents. Cells displayed glutamate uptake currents and responded to nucleotides by intracellular Ca(2+) increases. However, there were also species differences, such as a lack of GABA(A) receptors and of Ca(2+)-dependent K(+) currents in monkey cells. Thus, the use of Muller cells from cynomolgus monkeys may be advantageous for investigating a few specific properties; in general, monkey cells are no more similar to human cells than those from standard laboratory animals.

Adult↗

PubMed2005

Triamcinolone does not alter glial cell activation in the experimentally detached rabbit retina.

AIMS: Retinal detachment induces neural and photoreceptor cell degeneration and fast activation of micro- (immune) and macroglial cells. Hypoxia caused by increased distance between the choriocapillaris and the neural retina, and retinal oedema during detachment, are factors causing gliotic responses and cell degeneration. Triamcinolone may inhibit some cellular responses that accompany hypoxia. Therefore, we investigated whether triamcinolone acetonide may be effective to reduce the gliotic alterations in the detached retina. METHODS: Local retinal detachment in rabbit eyes was created by subretinal injection of sodium hyaluronate, and triamcinolone acetonide (8 mg) was applied intravitreally. Wholecell patch-clamp records from Muller cells and Ca2+ imaging from retinal wholemounts were carried out. Microglial/immune cells in the nerve-fiber layer of retinal wholemounts were labeled with Griffonia simplicifolia agglutinin (GSA) isolectin. Additionally, two morphological parameters which characterize microglial activation/immune cell infiltration were estimated: the cross-sectional area of the somata of the cells in the nerve-fiber layer and the number of cell processes which evolve from the soma. RESULTS: Three days after detachment, gliotic alterations were apparent in Muller cells isolated from both detached and nondetached retinal areas, as indicated by the cellular hypertrophy, by the downregulation of the plasma membrane K+ conductance, and by the upregulation of intracellular Ca2+ responsiveness to stimulation of purinergic P2Y receptors. Intravitreal triamcinolone did not alter these gliotic alterations of Muller cells. Furthermore, triamcinolone could not inhibit the immune cell activation present in detached and attached retinal areas. However, intravitreal triamcinolone led to a strong decrease in the process number of GSA lectin-positive cells from detached retinas. CONCLUSIONS: The results suggest that triamcinolone is ineffective to inhibit gliotic responses in the detached retina. However, the immune cell activation after detachment was partially influenced by triamcinolone.

Animals↗

PubMed2005

Neuronal versus glial cell swelling in the ischaemic retina.

Under normal conditions, the pigment epithelium dehydrates the outer retina while Müller glial cells mediate the rapid water transport within the inner retina. Gliotic alterations of Müller cells may be implicated in the development of oedema in the post-ischaemic retina. Here, we suggest a mechanism of Müller cell-supported neuronal cell swelling and apoptosis in the ischaemic retina. During ischaemia, over-excitation of ionotropic glutamate receptors leads to neuronal cell depolarization that causes excess Ca(2+) influx into the cells, and to activation of the apoptosis machinery. The ion fluxes into the retinal neurons are associated with water movements that are mediated by aquaporin-4 water channels expressed by Müller cells and result in neuronal cell swelling. After reperfusion, the glial cells may swell due to the down-regulation of their K(+) conductance, which results in intracellular K(+) overload and water movements from the blood and vitreous into the cells. An inhibition of the glial cell-mediated water movements during ischaemic episodes should reduce the ion shifts at the neuronal synapses, resulting in decreased neuronal cell swelling and apoptosis. An inhibition of the water movements in the post-ischaemic phase may prevent cytotoxic Müller cell swelling but may impair the fluid clearance from retinal tissue in the presence of vasogenic oedema. Thus, pharmacological modification of the ion and fluid clearance functions of Müller cells may become a novel way to resolve both cytotoxic and vasogenic oedema in the retina.

Animals↗

PubMed2005

Resensitization of P2Y receptors by growth factor-mediated activation of the phosphatidylinositol-3 kinase in retinal glial cells.

PURPOSE: To determine whether activation of receptor tyrosine kinases enhances the responsiveness of purinergic P2Y receptors in Muller glial cells, known to induce Muller cell proliferation. METHODS: The P2Y receptors of primary cultured Muller cells of the guinea pig were desensitized by short (30 seconds to 10 minutes)- and long (24 or 48 hours)-term application of adenosine 5'-triphosphate (ATP). Recordings of ATP-evoked intracellular calcium responses showed whether short-term application of different growth factors evoke a resensitization of the receptors. Coapplication of pharmacologic inhibitors showed whether activation of protein kinases is involved in receptor resensitization. RESULTS: Both short- and long-term incubation with ATP induced a significant P2Y receptor desensitization, which was indicated by a strongly reduced intracellular calcium mobilization and which lasted for at least 48 hours. However, the receptors were significantly resensitized after short-term application of platelet-derived, epidermal, or nerve growth factors. The growth factor-mediated resensitization was dependent on an intact cytoskeleton and on the activation of protein phosphatases and of the phosphatidylinositol-3 kinase (PI3K), but was independent of the activation of protein kinase C, src kinases, or extracellular signal-regulated kinases. CONCLUSIONS: The results show that activation of receptor tyrosine kinases causes, via activation of PI3K and protein phosphatases, a resensitization of P2Y receptors formerly desensitized by agonist application. The growth factor-mediated resensitization may underlie the previously observed enhanced responsiveness of P2Y receptors in retinal glial cells in experimental retinal detachment and proliferative vitreoretinopathy and may contribute to the induction of reactive gliosis and Muller cell proliferation.

Adenosine Triphosphate↗

PubMed2005

Ischemia-reperfusion causes exudative detachment of the rabbit retina.

PURPOSE: To characterize the activation of macroglial (Müller) and microglial cells, as well as neuronal cell degeneration, during ischemia-reperfusion in rabbit retina and to test the possible effect of triamcinolone acetonide on gliosis. METHODS: Transient retinal ischemia was produced by increasing intraocular pressure for 60 minutes. Triamcinolone (8 mg) was intravitreally applied immediately after the cessation of ischemia. At 3 and 8 days after reperfusion, the K+ currents of acutely isolated Müller cells were recorded, and the Ca2+ responses of Müller cells on stimulation of P2Y receptors were recorded fluorometrically in retinal wholemounts. Microglial/immune cells in the nerve fiber layer of retinal wholemounts were labeled with isolectin. To evaluate neuronal and Müller cell loss, the numbers of cells were counted in retinal slices. RESULTS: Transient ischemia caused exudative detachment of the central retina that was characterized by disruption of the pigment epithelial monolayer, the presence of scattered pigment epithelial and immune cells in the expanded subretinal space, and retinal folds. A significant loss of photoreceptor cells was observed at 8 days after reperfusion. At 3 and 8 days after reperfusion, Müller cell gliosis was apparent, as indicated by cellular hypertrophy, downregulation of K+ channel expression, and an increased number of cells that displayed P2Y receptor-mediated Ca2+ responses. The number of microglial/immune cells increased strongly after reperfusion. Intravitreal triamcinolone did not affect the parameters of Müller cell gliosis but decreased the number of microglial/immune cells. CONCLUSIONS: Ischemia-reperfusion of the rabbit retina causes exudative retinal detachment that is characterized by a loss of photoreceptor cells, whereas the inner retina remains largely preserved. Micro- and macroglial cells are activated early during reperfusion, even before dropout of the photoreceptor cells. Intravitreal triamcinolone may decrease the degree of microglial/immune cell activation.

Animals↗