Biomedical subjects

L Dang

Publications and source records attributed to L Dang.

15 recordsLinked to original sources

PubMed2006

Effects of IKK inhibitor PS1145 on NF-kappaB function, proliferation, apoptosis and invasion activity in prostate carcinoma cells.

A key antiapoptotic transcription factor, nuclear factor kappa-B (NF-kappaB), is known to be critically important for tumor cell growth, angiogenesis and development of metastatic lesions. We and others showed previously that NF-kappaB transcription factor was constitutively activated in androgen-independent prostate carcinoma (PC) cell lines due to the upregulated activity of inhibitor of NF-kappaB kinases (IKK). In this work, using luciferase assay, electrophoretic mobility shift assay and Northern blot analysis of expression of endogenous kappaB-responsive genes, we demonstrate that a novel highly specific small-molecule IKK inhibitor, PS1145, efficiently inhibited both basal and induced NF-kappaB activity in PC cells. We found that PS1145 induced caspase 3/7-dependent apoptosis in PC cells and significantly sensitized PC cells to apoptosis induced by tumor necrosis factor alpha. We also showed that PS1145 inhibited PC cell proliferation. Effects of PS1145 on proliferation and apoptosis correlated with inhibition of interleukin (IL)-6, cyclin D1, D2, inhibitor of apoptosis (IAP)-1 and IAP-2 gene expression and decreased IL-6 protein level. In addition, we found that incubation with PS1145 inhibited the invasion activity of highly invasive PC3-S cells in invasion chamber assay in a dose-dependent manner. Overall, this study provides the framework for development of a novel therapeutic approach targeting NF-kappaB transcription factor to treat advanced PC.

Animals↗

PubMed2006

Notch3 signaling initiates choroid plexus tumor formation.

Notch3 has been studied in the context of brain development, but whether it plays a role in the formation of brain tumors is unclear. We demonstrate that the introduction of constitutively active Notch3 into periventricular cells of embryonic day 9.5 mice causes the formation of choroid plexus tumors (CPTs). Tumors arose in the fourth ventricles in 83% of animals and were associated with hydrocephalus. They were microscopically highly similar to choroid plexus papillomas in humans, with an ongoing proliferation rate of 4-6%. Signs of Notch pathway activity were also present in human choroid plexus lesions, and receptor mRNA levels in papillomas were elevated over those in non-neoplastic choroid plexus. Notch2 was overexpressed approximately 500-fold in one case, suggesting that the role of this pathway in CPTs may not be specific to Notch3. Our findings indicate that activated Notch3 can function as an oncogene in the developing brain, and link the Notch pathway to human CPT pathogenesis.

Animals↗

PubMed2005

Evaluation of ablation patterns using a biophysical model of atrial fibrillation.

Atrial fibrillation (AF) is the most common form of cardiac arrhythmia. Surgical/Radiofrequency (RF) ablation is a therapeutic procedure that consists of creating lines of conduction block to interrupt AF. The present study evaluated 13 different ablation patterns by means of a biophysical model of the human atria. In this model, ablation lines were abruptly applied transmurally during simulated sustained AF, and success rate, time to AF termination and average beat-to-beat interval were documented. The gold standard Cox's Maze III procedure was taken as reference. The effectiveness of twelve less invasive patterns was compared to it. In some of these incomplete lines (entailing a gap) were simulated. Finally, the computer simulations were compared to clinical data. The results show that the model reproduces observations made in vivo: (1) the Maze III is the most efficient ablation procedure; (2) less invasive patterns should include lines in both right and left atrium; (3) incomplete ablation lines between the pulmonary veins and the mitral valve annulus lead to uncommon flutter; (4) computer simulations of incomplete lines are consistent with clinical results of non-transumural RF ablation. Biophysical modeling may therefore be considered as a useful tool for understanding the mechanisms underlying AF therapies.

Atrial Fibrillation↗

PubMed2001

Glutathione peroxidase-1 deficiency leads to increased nuclear light scattering, membrane damage, and cataract formation in gene-knockout mice.

PURPOSE: Previous in vitro studies with transgenic and gene-knockout mice have shown that lenses with elevated levels of glutathione peroxidase (GPX)-1 activity are able to resist the cytotoxic effect of H(2)O(2), compared with normal lenses and lenses from GPX-1-deficient animals. The purpose of this study was to investigate the functional role of this enzyme in antioxidant mechanisms of lens in vivo by comparing lens changes of gene-knockout mice with age-matched control animals. METHODS: In vivo lens changes were monitored by slit lamp biomicroscopy, and enucleated lenses were examined under a stereomicroscope in gene-knockout animals and age-matched control animals ranging in age from 3 weeks to 18 months. Transmission (TEM) and confocal microscopy were performed on different regions of lenses after the mice were killed at various times. RESULTS: Slit lamp images showed an increase in nuclear light scattering (NLS) in gene-knockout mice compared with control animals. TEM revealed changes in the nucleus as early as 3 weeks of age by the appearance of waviness of fiber membranes. With increasing age, there was greater distortion of fiber membranes and distension of interfiber space at the apex of fiber cells compared with control mice. The changes in nuclear fiber membranes were even more dramatic, as observed by confocal microscopy, which was performed on thicker sections. In contrast to the changes in the lens nucleus, the morphology of the epithelium and superficial cortex remained unchanged in knockout animals during the same experimental period, consistent with slit lamp observations. Stereomicroscopy of ex vivo lenses demonstrated a significant increase in opacification in gene-knockout mice relative to control animals of the same age. This effect became evident in mice aged 5 to 9.9 months and persisted thereafter in older animals, resulting in mature cataracts after 15 months. CONCLUSIONS: The results demonstrate the critical role of GPX-1 in antioxidant defense mechanisms of the lens nucleus. The increased NLS appears to be associated with damage to fiber membranes in the nucleus, which is particularly susceptible to oxidative challenge because of the deficiency of GPX-1. It is suggested that the lens membrane changes in the knockout animals may be due to the formation of lipid peroxides, which serve as substrates for GPX-1. Cataract development in gene-knockout mice appeared to progress from focal opacities, apparent at an earlier age, to lamellar cataracts between 6 and 10 months, and finally to complete opacification in animals older than 15 months. This is the first reported phenotype in GPX-1-knockout mice.

Animals↗

PubMed1998

Regulation of corneal endothelial barrier function by adenosine, cyclic AMP, and protein kinases.

PURPOSE: To determine which processes or factors that regulate corneal hydration are responsible for the hydration-modulating effects of adenosine. Influx of fluid to the stroma and efflux to the aqueous humor are governed, respectively, by the imbibition pressure of the stromal matrix and the transendothelial ionic gradients determined by the permeability and active transport characteristics of this monolayer. The focus of this study was to assess the effects of adenosine on these endothelial parameters. METHODS: Isolated corneas freshly dissected from rabbit eyes were used throughout. Active ion transport was assessed by measurement of 86Rb+ uptake by the endothelial cells of intact corneas incubated for 30 minutes in 25 mM HCO3(-)-Ringer with agents promoting corneal deturgescence or corneal swelling. Intracellular and extracellular fluid in the scraped endothelial cell mass was estimated from simultaneous counts of 3H-mannitol and 14C-urea, allowing calculation of tissue-to-medium (T-M) ratios of 86Rb+ in cell water. Permeability of the endothelium was determined by measuring the efflux into the superfusate of 5-carboxyfluorescein (CF) applied to the stroma of deepithelialized corneas superfused at the endothelial surface with the same media described for 86Rb+ uptake. Thickness of these corneas and of others fixed for scanning electron microscopy was monitored with a specular microscope. RESULTS: In the control medium, 25 mM HCO3(-)-Ringer, 86Rb+ was accumulated to yield a T-M ratio of 6.21. Neither adenosine nor other agents that increase cyclic adenosine monophosphate (cAMP)--that is, forskolin and dibutyryl cAMP--changed this value to a significant extent. Bumetanide had no effect, but ouabain caused a decrease in T-M to 1.30, a 79% inhibition. Elimination of Na+ or HCO3- also caused marked decreases in uptake. Permeability to CF in control medium was 3.40 x 10(-4) cm/min. A decrease of more than 20% (P < 0.05) was seen in the presence of adenosine and cAMP promoters and also with the protein kinase inhibitor H-8, whereas phorbol myristate acetate caused an increase to 4.50 x 10(-4) cm/min (P < 0.01). Ouabain caused no change, but blocked the effects of adenosine. Reducing the Ca2+ concentration of the superfusing medium caused time-dependent increases in permeability to 4.57 at 15 to 45 minutes and 12.5 at 80 to 110 minutes. At the earlier time, this increase in permeability could be prevented by the addition of adenosine or H-8. Elimination of Na+ or HCO3- ions from the medium caused a small decrease in permeability and, like ouabain, blocked the effect of adenosine. Changes in thickness of corneas were consistent, in most cases, with the observed alterations in 86Rb+ uptake or permeability to CF. Scanning electron microscopy showed contraction and rounding of endothelial cells in low Ca2+ medium, with stretching of intercellular borders, features that were largely eliminated when adenosine was also present. CONCLUSIONS: Adenosine, through increasing cAMP, decreases permeability of the corneal endothelium. This effect, rather than a change in the active transport (fluid pump) mechanism, is responsible for the promotion of deturgescence and maintenance of lower steady state thickness of corneas exposed to adenosine. The mechanism may involve the phosphorylation state of cytoskeletal proteins and seems to be dependent on an undisturbed environment of monovalent ions.

Adenosine↗

PubMed1997

Anti-beta-crystallin antibodies (mouse) or sera from humans with age-related cataract are cytotoxic for lens epithelial cells in culture.

Circulating autoantibodies against lens antigens are prevalent in patients with age-related cataract (ARC), but their pathogenic significance is unknown. We hypothesized that these autoantibodies are cytotoxic for lens epithelial cells (LECs). To test this hypothesis. We incubated LECs with mouse polyclonal or monoclonal antibodies against beta-crystallin (anti-beta) in the presence or absence of guinea pig complement. We found that anti-beta in the presence of the complement bound to and killed mouse LECs (MLECs) and human LECs (HLECs). Sera obtained from patients with ARC also were cytotoxic to both HLECs and MLECs in culture. Heat-inactivated human sera were not cytotoxic to LECs in the absence of the complement, but were cytotoxic to both HLECs and MLECs in the presence of additional complement. These results support the hypothesis that autoantibodies against lens antigens are cytotoxic to LECs, and that cell death may involve complement-mediated pathways.

Animals↗

PubMed1997

Peroxide-induced damage in lenses of transgenic mice with deficient and elevated levels of glutathione peroxidase.

Transgenic mice with elevated glutathione peroxidase (GSHPx) activity and gene knockout animals with a deficiency of the enzyme were used to investigate the role of GSHPx in defending the lens against H2O2-induced damage. The effects of peroxide on cultured lenses were determined by using light and transmission electron microscopy to evaluate morphological changes occurring in the epithelium and superficial cortex of the central and equatorial regions of the lens. DNA single-strand breaks in the epithelium were also examined. Following a 30-min exposure to 25 microM H2O2, lenses from normal animals showed distinct changes in the morphology of both the epithelium and superficial cortex. The damage to these cells was extensive in lenses of gene knockout mice in which activity of GSHPx was undetectable. In marked contrast, lenses of transgenic mice, which had 5-fold higher activities of GSHPx, were able to resist the cytotoxic effects. Similar to damage to cell morphology, the extent of DNA strand breaks was significantly lower (40% of control) in H2O2-exposed lenses as compared to normal lenses while DNA damage in gene knockout lenses was 5 times greater than that of GSHPx-rich transgenic lenses. The present studies extend our previous findings on the role of the glutathione redox cycle in the detoxification of peroxide and demonstrate that an increase in GSHPx activity protects the lens against peroxide-induced changes in cell morphology and DNA strand breaks.

Animals↗

PubMed1997

An assessment of rat photoreceptor sensitivity to mitochondrial blockade.

PURPOSE: To report results of functional, biochemical and structural studies of photoreceptor mitochondria in isolated rat retinas under conditions of mitochondrial inhibition. METHODS: Dark-adapted rat retinas were incubated in a modified Ringer's bicarbonate medium under aerobic and anaerobic conditions. Several different procedures were used to inhibit mitochondrial function; N2, 0.01 mM antimycin A, and 1 and 10 mM potassium cyanide (KCN). Measurements were made of lactic acid production, retinal adenosine triphosphate (ATP) content, and receptor potentials. Morphology of the inner segment mitochondria was examined by electron microscopy. RESULTS: In the presence of N2, 0.01 mM antimycin, or 1 mM KCN, lactic acid production was linear throughout the 60- minute period; and the rate was similar for each condition. Retinal ATP content and the amplitude of the receptor potential were also maintained at high levels after short-term incubations with either N2, antimycin A, or 1 mM KCN. In contrast, use of 10 mM KCN produced an entirely different set of results. These effects were studied both at the alkaline pH (8.9) found when this concentration of KCN was simply added to bicarbonate-buffered media and at the normal pH (after readjustment) of 7.4. With 10 mM KCN (pH 8.9), retinal lactate production was severely depressed, retinal ATP content was nearly depleted within 5 to 10 minutes, and the amplitude of the receptor potential rapidly declined to a low level. The deleterious effects of 10 mM KCN on these parameters were lessened to varying degrees when pH was readjusted to 7.4. Electron microscopic observations of rat rod inner segments indicated generally excellent survival of these organelles after incubation with either N2, antimycin A, or 1 mM KCN in comparison with their appearance under oxygenated conditions. However, the inner segments were significantly disrupted after incubation of retinas with 10 mM KCN. CONCLUSIONS: Findings suggest that the loss of the receptor potential and depletion of ATP observed with minutes after exposing isolated rat retinas to media containing 10 mM KCN results from the inhibition of both respiration and glycolysis by this high concentration of KCN. In contrast, when conditions are chosen so that only respiration is impaired (as with N2, antimycin A, or 1 mM KCN) photoreceptor cells are resistant to short-term episodes of mitochondrial inhibition, principally because the upregulation of glycolysis generates sufficient ATP to compensate reasonably well for the loss in mitochondrially produced ATP.

Adenosine Triphosphate↗

PubMed1996

The effect of ionizing radiation on signal transduction: antibodies to EGF receptor sensitize A431 cells to radiation.

What determines the degree of cell-resistance or sensitivity to ionizing radiation is not yet known. As a corollary to the ability of ceramide to induce apoptosis, some questions arise as to whether malignant cells escape apoptosis because of their inability to mount a ceramide response to inducers of apoptosis. To shed more light on the molecular mechanisms of tumor cell response to radiation, we tested whether exposure to ionizing radiation (of 200-1000 cGy) is associated with changes in ceramide levels in A431 tumor epithelial cells and whether the ability of ceramide to induce apoptosis is inhibited by protein kinase C (PKC) activation. Our studies demonstrate an immediate decrease in cellular levels of ceramide in response to radiation, while sphingosine levels increase. Under the same conditions the cellular 1,2-diacylglycerol (DAG) levels decrease as well, being accompanied by the translocation of PKC alpha from the membrane to the cytoplasm. Elevation of membrane PKC levels by 12-O-tetradecanoylphorbol 13-acetate (TPA) treatment had no effect on cell survival after irradiation, while treatment with EGF during and after irradiation augmented cell survival. Moreover, monoclonal antibodies to the EGF receptor (EGFR) sensitize cells to radiation by facilitating radiation-induced apoptosis. It is thus plausible that in human Squamous carcinoma cells, radiation activates predominantly the EGFR to induce resistance, while both sphingomyelin and PKC signal transduction pathways are deactivated and demonstrate no significant role in the modulation of the sensitivity or the resistance of A431 cells to ionizing radiation.

Antibodies↗

PubMed1995

Nuclear light scattering, disulfide formation and membrane damage in lenses of older guinea pigs treated with hyperbaric oxygen.

Nuclear cataract, a major cause of loss of lens transparency in the aging human, has long been thought to be associated with oxidative damage, particularly at the site of the nuclear plasma membrane. However, few animal models have been available to study the mechanism of the opacity. Hyperbaric oxygen (HBO) has been shown to produce increased nuclear light scattering (NLS) and nuclear cataract in lenses of mice and human patients. In the present study, older guinea pigs (Initially 17-18 months of age) were treated with 2.5 atmospheres of 100% O2 for 2-2.5-hr periods, three times per week, for up to 100 times. Examination by slit-lamp biomicroscopy showed that exposure to HBO led to increased NLS in the lenses of the animals after as few as 19 treatments, compared to lenses of age-matched untreated and hyperbaric air-treated controls. The degree of NLS and enlargement of the lens nucleus continued to increase until 65 O2-treatments, and then remained constant until the end of the study. Exposure to O2 for 2.5 instead of 2 hr accelerated the increase in NLS; however, distinct nuclear cataract was not observed in the animals during the period of investigation. A number of morphological changes in the experimental lens nuclei, as analysed by transmission electron microscopy, were similar to those recently reported for human immature nuclear cataracts (Costello, Oliver and Cobo, 1992). O2-induced damage to membranes probably acted as scattering centers and caused the observed increased NLS. A general state of oxidative stress existed in the lens nucleus of the O2-treated animals, prior to the first appearance of increased NLS, as evidenced by increased levels of protein-thiol mixed disulfides and protein disulfide. The levels of mixed disulfides in the experimental nucleus were remarkably high, nearly equal to the normal level of nuclear GSH. The level of GSH in the normal guinea pig lens decreased with age in the nucleus but not in the cortex; at 30 months of age the nuclear level of GSH was only 4% of the cortical value. HBO-induced changes in the lens nucleus included loss of soluble protein, increase in urea-insoluble protein and slight decreases in levels of GSH and ascorbate; however, there was no accumulation of oxidized glutathione. Intermolecular protein disulfide in the experimental nucleus consisted mainly of gamma-crystallin, but crosslinked alpha-, beta- and zeta-crystallins were also present.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

The effect of ganglioside on oxidation-induced permeability changes in lens and in epithelial cells of lens and retina.

Several recent reports have indicated that ganglioside treatment both in vivo and in vitro has a protective effect on the loss of membrane permeability resulting from inhibition of transport enzyme(s) in different experimental models. In this study we have investigated the effect of monosialoganglioside on oxidation-induced changes in organ-cultured rabbit lenses and in cultured dog lens epithelium and human retinal pigment epithelial cells. Exposure of organ-cultured lenses to 0.5 mM hydrogen peroxide for 1 hr increased the efflux of 86Rb from intact lenses and loss of myoinositol from the capsule epithelium. Pretreatment of the lenses with monosialoganglioside significantly reduced the efflux rate of 86Rb and loss of myoinositol. Monosialoganglioside also prevented morphological changes induced by 0.1 mM hydrogen peroxide in dog lens epithelium and loss of cell viability caused by docosahexaenoic acid in dog lens epithelium and in human retinal pigment epithelial cells. In contrast to the protective effect of monosialoganglioside on permeability and morphological changes in cultured cells, it had no effect against single-strand breaks of DNA in dog lens epithelium resulting from exposure to hydrogen peroxide, X-ray and UV-B radiation. Although the molecular mechanisms by which monosialoganglioside prevents permeability and morphological changes induced by hydrogen peroxide and docosahexaenoic acid are not known, it appears that this ganglioside serves as a membrane stabilizer rather than as a free-radical scavenger.

Animals↗

PubMed1991

In utero and milk-mediated effect of aldose reductase inhibitor on galactose cataracts.

Our previously reported investigations showed that cataracts could be induced in fetal lenses through the maternal feeding of galactose during pregnancy. We also reported that the lens opacity present at birth reverses completely by 30 days of age if there is no further post-natal exposure to galactose. This investigation was designed to investigate if an aldose reductase inhibitor (ARI) has any cross-placental effect in preventing galactose-induced cataracts in fetuses. We have also evaluated if there are any milk-mediated effects of galactose on cataract induction and of galactose and ARI on the maintenance or reversal of opacities induced in utero. Pregnant Sprague-Dawley rats were fed either 50% galactose or rat chow with or without the ARI, (2R,4S)-6-fluoro-2-methyl spirochroman-4,4'-imidazolidine-2',5'-dione (Eisai compound E-0722). Following parturition, pups of mothers from the different dietary groups were either fed by their own mothers or foster fed by lactating females fed either rat chow or 50% galactose with or without the ARI. Lenses of the pups were examined at desired intervals with light and scanning electron microscopes. We observed that: (a) both galactose and the ARI had a cross-placental effect on the fetal lenses in the development and inhibition of cataracts, respectively; (b) galactose had very little, if any, milk-mediated effect on either the induction of cataracts in newborn pups that were born with transparent lenses or the maintenance of cataracts induced in utero; (c) the ARI appeared to have a milk-mediated effect, which accelerates the reversal of cataract associated alterations in lenses of pups with cataracts induced in utero, leading to further reinstatement of lens transparency; and (d) the presence of ARI in the diet of rats during pregnancy and/or post-parturition provided continued protection to the lenses of pups that were exposed to a galactose diet following birth.

Aldehyde Reductase↗

PubMed1989

Elemental and structural studies of the rat galactose cataract.

A series of rat galactose lenses, from 1 to 20 days on the 50% galactose diet, were frozen in the whole eye, and fractured from pole to pole in the frozen state. Lyophilized half-lenses were prepared for analysis by energy dispersive spectrometry (EDS). Following elemental analysis, some specimens were embedded and sectioned for histological studies. Elemental X-ray maps, and/or profiles, were made for K, Na, Cl, Ca, P, and S. As early as two days on the galactose diet, a crescent-shaped region ("streak") of Cl, Na, and Ca gain, and K loss develops near the equatorial surface. Between this region and the equatorial surface are the nucleated differentiating fiber cells which maintain low Cl, Na, and Ca, and high K (viable equatorial zone, VEZ). With time the "streak" expands anteriorly, centrally and posteriorly, eventually (by 20 days) including most of the lens. The VEZ, including the epithelium, however, is non-reactive to the galactose diet, which is deleterious to the fully differentiated fiber cells. Eventually, the VEZ undergoes a characteristic morphological change, apparently due in part to changes in its physical environment.

Animals↗

PubMedDate not supplied

Nitric oxide synthesis in retinal photoreceptor cells.

Nitric oxide (NO) is known to be synthesized in several tissues and to increase the formation of cyclic GMP through the activation of soluble guanylate cyclases. Since cyclic GMP plays an important role in visual transduction, we investigated the presence of nitric oxide synthesizing activity in retinal rod outer segments. Bovine rod outer segments were isolated intact and separated into membrane and cytosolic fractions. Nitric oxide synthase activity was assayed by measuring the conversion of L-arginine to L-citrulline. Both membrane and cytosolic fractions were active in the presence of calcium and calmodulin. The activity in both fractions was stimulated by the nitric oxide synthase cofactors FAD, FMN, and tetrahydrobiopterin and inhibited by the L-arginine analog, L-monomethyl arginine. The Km for L-arginine was similar, about 5 microM for the enzyme in both fractions. However, the two fractions differed in their calcium/calmodulin dependence: the membrane fraction exhibited basal activity even in the absence of added calcium and calmodulin while the cytosolic fraction was inactive. But the activity increased in both fractions when supplemented with calcium/calmodulin: in membranes from about 40 to 110 fmol/min/mg of protein and in the cytosol from near zero to about 350 fmol/min/mg of protein in assays carried out at 0.3 microM L-arginine. The two enzymes also responded differently to detergent: the activity of the membrane enzyme was doubled by Triton X-100 while that of the cytosolic enzyme was unaffected. These results show that NO is produced by cytosolic and membrane-associated enzymes with distinguishable properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗

PubMedDate not supplied

Soluble guanylate cyclase and nitric oxide synthase in synaptosomal fractions of bovine retina.

Cyclic GMP has been shown in recent years to directly activate ion channels in bipolar and ganglion cells, and to indirectly regulate coupling between horizontal cells, and between bipolar and amacrine cells. In all of these cases, the effects of cyclic GMP are mimicked by nitric oxide. An increase in calcium concentration stimulates the production of nitric oxide by neuronal and endothelial forms of nitric oxide synthase, which in turn activates soluble guanylate cyclases, enhancing the synthesis of cyclic GMP. Though some effects of nitric oxide do not involve cyclic GMP, the nitric oxide-cyclic GMP cascade is well recognized as a signaling mechanism in brain and other tissues. The widespread occurrence of nitric oxide/cyclic GMP-regulated ion channel activity in retinal neurons raises the possibility that nitric-oxide-sensitive soluble guanylate cyclases play an important role in cell-cell communication, and possibly, synaptic transmission. Immunohistochemical studies have indicated the presence of soluble guanylate cyclase in retinal synaptic layers, but such studies are not suitable for determination of the density or quantitative subcellular distribution of the enzyme. Microanalytical methods involving microdissection of frozen retina also showed the presence of cyclase activity in retinal plexiform layers but these methods did not permit distinction between nitric oxide-sensitive and insensitive cyclases. In this study, we fractionated retinal homogenate into the cytosolic and synaptosomal fractions and investigated the specific activity and distribution of soluble guanylate cyclase and nitric oxide synthase. The results show that both enzymes are present in the synaptosomal fractions derived from inner and outer plexiform layers. The synaptosomal fraction derived from inner retina was highly enriched in cyclase activity. Nitric oxide synthase activity was also higher in the inner than outer retinal synaptosomal fraction. The results suggest that the nitric oxide-cyclic GMP system is operational in both synaptic layers of retina and that it may play a more significant role in the inner retina.

Animals↗