Biomedical subjects

P Walter

Publications and source records attributed to P Walter.

At least 145 records · Page 8Linked to original sources

PubMed1996

The cumulative normalised rim/disc area ratio curve.

BACKGROUND: The assessment of the cup of the optic disc depends, among other criteria, on the disc area. A small cup in a small optic disc can indicate an advanced glaucomatous lesion, while on the other hand a large cup in a large optic disc can be normal. Therefore, a cumulative normalised rim/disc area ratio curve could help to distinguish between glaucomatous and normal optic cups. The aim of our study was to calculate normalised rim/disc area ratio curve. METHODS: Heidelberg Retina Tomograph examinations of the optic nerve head of 100 randomly selected eyes of 100 normal subjects were evaluated. We calculated the disc area-adjusted normalised rim/disc area ratio in sectors of 10 degrees. The 95th, 90th and 50th percentiles of each of the 36 sectors were displayed in descending order. RESULTS: In relation to the normal percentile curves, it is possible to display an individual normalised rim/disc area ratio curve. We obtained such curves for a normal optic disc, optic nerve heads with moderate and advanced lesions and a small optic disc with glaucomatous damage. CONCLUSION: We present a new display mode for the results of Heidelberg Retina Tomograph optic nerve head examination, which may be helpful for easy and reliable assessment of the local, diffuse and combined components of glaucomatous optic nerve head damage depending on optic disc size.

Adult↗

PubMed1996

Prognostic factors associated with the visual outcome after vitrectomy for endophthalmitis.

BACKGROUND: Functional results following vitrectomy with intraocular and systemic antibiotic treatment for endophthalmitis are influenced by numerous factors. METHODS: A retrospective study of 65 cases of endophthalmitis treated between October 1988 and May 1994 at the Department of Ophthalmology, University of Cologne, Germany was conducted. All eyes underwent pars plana vitrectomy and intraocular and systemic antibiotic treatment. RESULTS: Vision of 20/400 or better could be obtained in 66% of eyes following extracapsular cataract extraction and intraocular lens implantation (ECCE + IOL), in 62% after severe eye injury, in 36% of eyes after intraocular surgery for other reasons than cataract extraction with lens implantation and in 33% of patients with endogenous endophthalmitis. Vision of 20/50 or better could be achieved in 41% of eyes following ECCE + IOL and additional systemic steroid treatment. In 22% of cases primary silicone endotamponade was performed; 57% of these eyes obtained visual acuity of 20/400 or better. Fifteen patients (23%) suffered diabetes mellitus; 20/400 vision or better could be achieved in 73% of these eyes. Visual acuity of hand movements or better before vitrectomy was associated with 20/400 vision or better in 69% of cases, whereas ambulatory vision could be attained in only 33% of patients with visual acuity of worse than hand movements at the initial presentation. Visual acuity of less than 20/400 was found in all eyes with haemolytic streptococcal infections. CONCLUSION: Prompt treatment of endophthalmitis is crucial. Additional treatment using systemic steroids and, if necessary, silicone oil can improve the functional outcome in some cases.

Adult↗

PubMed1996

[Effects of fluorescein and indocyanine green angiography on subsequent dark adaptation and the electroretinogram].

BACKGROUND: In clinical practice the electroretinogram (ERG) usually should not be recorded immediately after conventional fluorescein angiography (FLA), because of the bleaching effects of strong light exposure on the course of dark adaptation and on the ERG. Currently it is not known, if indocyaningreen (ICG) angiography using the Heidelberg Retina Angiograph (HRA) has similar effects on the outer retina and if therefore the ERG should also not be recorded after ICG angiography. METHODS: Eight patients with different retinal diseases were examined. After 5 minutes of light adaptation to 160 cd/m2, Ganzfeld ERGs were repeatedly recorded using DTL electrodes during a 30 minutes dark period with a flash luminance of 0.1 cds/.m2. After this dark adaptation period a standardized ERG was recorded according to the ISCEV recommendations. This procedure was followed either by ICG angiography using the HRA or by conventional fluorescein angiography using the Canon CF 60 fundus camera. Within an interval of 5 minutes the above mentioned ERG procedure was repeated. RESULTS: ICG angiography using the HRA did neither affect the course of dark adaptation as measured by increasing b-wave amplitudes during the 30 minutes dark adaptation period, nor the values for each response of the Ganzfeld standard ERG. FLA did neither affect b-wave responses to dim stimuli, nor to stronger stimuli in the scotopic range. However, the course of dark adaptation was significantly prolonged after FLA. The maximum b-wave was not affected. CONCLUSIONS: ICG angiography using the HRA could be performed prior to the recording of the ERG, without any effect on the ERG. In contrast conventional FLA must be performed after ERG recordings, in order not to alter the electrophysiological responses.

Adult↗

PubMed1996

ER membrane protein complex required for nuclear fusion.

Diploid cells of the yeast Saccharomyces cerevisiae form after the mating of two haploid cells of the opposite mating type. After fusion of the two plasma membranes of the mating cells, a dinucleated cell forms initially in which the two haploid nuclei then rapidly fuse to form a single diploid nucleus. This latter event, called karyogamy, can be divided into two distinct steps: the microtubule-based movement that causes the two nuclei to become closely juxtaposed and the fusion of the nuclear membranes. For the membrane fusion step, one required component, the ER luminal protein Kar2p (BiP), has been identified. For topological reasons, however, it has been unclear how Kar2p could function in this role. Kar2p is localized to the luminal (i.e., noncytoplasmic) face of the ER membrane, yet nuclear fusion must initiate from the cytosolic side of the outer nuclear membrane or the ER membrane with which it is contiguous. There is both genetic and biochemical evidence that Kar2p interacts with Sec63p, an ER membrane protein containing both luminal and cytosolic domains that is involved in protein translocation across the membrane. We have isolated novel sec63 mutant alleles that display severe karyogamy defects. Disruption of the genes encoding other Sec63p-associated proteins (Sec71p and Sec72p) also results in karyogamy defects. A suppressor mutant (sos1-1) partially corrects the translocation defect but does not alleviate the karyogamy defect. sec61 and sec62 mutant alleles that cause similar or more severe protein translocation defects show no karyogamy defects. Taken together, these results suggest a direct role for Sec63p, Sec71p, and Sec72p in nuclear membrane fusion and argue against the alternative interpretation that the karyogamy defects result as an indirect consequence of the impaired membrane translocation of another component(s) required for the process. We propose that an ER/nuclear membrane protein complex composed of Sec63p, Sec71p, and Sec72p plays a central role in mediating nuclear membrane fusion and requires ER luminally associated Kar2p for its function.

Endoplasmic Reticulum↗

PubMed1996

Signal sequences specify the targeting route to the endoplasmic reticulum membrane.

In the yeast Saccharomyces cerevisiae, only a subset of preproteins that are translocated across the ER membrane require the function of the signal recognition particle (SRP), suggesting that an alternative, SRP-independent pathway must exist (Hann, B.C., and P. Walter. 1991. Cell. 67:131-144). We have established that the two targeting pathways function in parallel. Mutant alleles of SEC62 and SEC63 were isolated that specifically impaired the translocation of SRP-independent preproteins in vivo and in vitro, whereas SRP-dependent preproteins were unaffected. Based on this analysis, preproteins fall into three distinct classes: SRP dependent, SRP independent, and those that can use both pathways. Pathway specificity is conferred by the hydrophobic core of signal sequences. Our studies show a previously unrecognized diversity in ER-directed signal sequences, that carry structural information that serves to identify the route taken.

Base Sequence↗

PubMed1996

Clinical efficacy of haemorheological treatment using plasma exchange, selective adsorption and membrane differential filtration in maculopathy, retinal vein occlusion and uveal effusion syndrome.

The aim of the study was to test the clinical efficacy of haemorheological treatment with extracorporeal techniques in ocular diseases. We treated patients suffering from maculopathies of different origin: age-related (AMD, n = 17), uveitis-associated (n = 14) and myopia-associated maculopathy (n = 5). We also treated patients with uveal effusion syndrome (n = 3) and central retinal vein occlusion (n = 4) resistant to haemodilution or steroid therapy. The treatment consisted of plasma exchange, selective adsorption with a tryptophan-polyvinylalcohol adsorber and membrane differential filtration. Maculopathy patients underwent two treatments while the other patients received between 1 and 7 treatments. Pulsatile ocular blood flow was measured in 10 patients before and after therapy. The main parameter for evaluating clinical outcome was the change in visual acuity. Severe side-effects did not occur. The rheological parameters including plasma viscosity, whole blood viscosity and erythrocyte aggregation were statistically significantly lowered. Of 36 patients suffering from maculopathy, 25 showed an improvement of at least 1 line of visual acuity after therapy, 7/17 patients in AMD, 6/14 in uveitis and 0/5 in myopia improved 3 lines or more. All patients suffering from retinal vein occlusion improved at least 1 line and two showed an improvement of 3 lines or more. In uveal effusion syndrome, an improvement of 3 lines or more was reached in all patients. Plasma exchange, selective adsorption and membrane differential filtration are effective rheological treatment approaches to improving visual acuity in patients suffering from maculopathy except myopia-associated maculopathy. Efficacy in patients suffering from central retinal vein occlusion and uveal effusion syndrome was proven, even when the patients were resistant to previous haemodilution or steroid therapy. We conclude that a rheological approach should be considered before invasive methods such as laser coagulation, radiation therapy or surgery are applied.

Hemofiltration↗

PubMed1996

Apoptotic cell death in proliferative vitreoretinopathy.

Apoptosis is a selective event of physiological cell deletion that plays a crucial role in the development of numerous tissues, including the retina. In this paper we report the occurrence of apoptosis in epiretinal membranes derived from patients with proliferative vitreoretinopathy (PVR). Detection of apoptosis was performed by an in situ DNA-end labeling technique using terminal transferase-mediated deoxyuridine triphosphate (dUTP) incorporation. Apoptotic nuclei exhibiting chromatin condensation and fragmentation were also identified by acridine orange fluorescence. Apoptosis was detected in varying numbers of cells. The typical appearance of apoptotic nuclei, including nuclear chromatin condensation, was detected scattered inhomogeneously throughout the epiretinal membranes, in clusters, or even in single cells. Induction of apoptosis in human retinal pigment epithelial (RPE) cells by daunomycin could be demonstrated by in situ DNA end labeling and by quantitative determination of cytoplasmatic histone-associated DNA fragments using a photometric enzyme immunoassay. Since apoptosis has been shown to be an important factor in the growth control of various untransformed and neoplastic cell populations, the pharmacological induction of apoptosis in epiretinal membranes could result in a new approach toward inhibiting cellular proliferation in PVR.

Adult↗

PubMed1996

NMR studies of the most conserved RNA domain of the mammalian signal recognition particle (SRP).

Mammalian signal recognition particle (SRP) and its homologues exhibit a phylogenetically conserved RNA domain, whose predicted secondary structure exhibits a hairpin motif with two bulged regions. Two RNA fragments comprising one (24 nt) or two (43 nt) of the conserved bulges were studied. Each fragment binds specifically to the domain of the Escherichia coli homologue of the SRP54 protein, which is involved in signal sequence recognition. The SRP RNA fragments exhibited a pronounced structural stabilization in the presence of Mg2+. Assignments of all base, H1', H2', and most imino proton resonances in the presence of Mg2+ were obtained for the 24mer RNA via NOE spectroscopy and correlated homonuclear NMR methods. 2D NOE patterns permitted a coarse structural description, revealing a relatively compact A-type geometry for the 24mer without any indications of looped-out nucleotides, syn-oriented bases, or base triplets. The GGAA-loop is structurally very similar to that of the GCAA tetraloop [Heus HA, Pardi A, 1991, Science 253:191-194]. Mg2+ seems to stabilize the structure of the conserved bulged region, which involves G:A and C:A mismatch pairs. Deviations from ideal A-type helicity are found for a larger region than the predicted secondary structure implies. Although no explicit assignment effort has been dedicated to the 43mer yet, striking similarity in chemical shift changes upon addition of Mg2+ allowed some structural conclusions. The bulge present in both RNA fragments exhibits a similar, pronounced flexibility in the absence of Mg2+, indicating that the additional bulge in the 43mer does not stabilize the other bulge.

Binding Sites↗

PubMed1996

[Ovarian angioma. Report of 3 asymptomatic cases].

In 3 female patients, aged 46, 50 and 74 years respectively, ovarian angiomas measuring 3, 5 and 30 mm in diameter were discovered. All the angiomas were asymptomatic. They were either associated with endometrioid carcinoma or uterine leiomyomas, or detected casually by ultrasound scan in a patient with ascites, intrahepatic nodule and increased serologic CA 125. The immunohistochemical studies failed to reveal any affinity between the vascular endothelium of our ovarian angiomas and oestrogen and progesterone receptors.

Aged↗

PubMed1996

[Endovascular therapy of visceral aneurysms].

Sixteen cases of endovascular treatment of aneurysms and pseudoaneurysms were reported; five patients had true aneurysms, 11 presented pseudoaneurysms of splanchnic arteries. In all cases embolization was performed with coils; in one case we used coils in combination with Ethibloc. In 14 of 16 patients definite occlusion of the aneurysms was achieved without further surgical intervention.

Adult↗

PubMed1995

Reciprocal stimulation of GTP hydrolysis by two directly interacting GTPases.

The Escherichia coli guanosine triphosphate (GTP)-binding proteins Ffh and FtsY have been proposed to catalyze the cotranslational targeting of proteins to the bacterial plasma membrane. A mutation was introduced into the GTP-binding domain of FtsY that altered its nucleotide specificity from GTP to xanthosine triphosphate (XTP). The mutant FtsY protein stimulated GTP hydrolysis by a ribonucleoprotein consisting of Ffh and 4.5S RNA in a reaction that required XTP, and it hydrolyzed XTP in a reaction that required both the Ffh-4.5S ribonucleoprotein and GTP. Thus, nucleotide triphosphate hydrolysis by Ffh and FtsY is likely to occur in reciprocally coupled reactions in which the two interacting guanosine triphosphatases act as regulatory proteins for each other.

Amino Acid Sequence↗

PubMed1995

SRP samples nascent chains for the presence of signal sequences by interacting with ribosomes at a discrete step during translation elongation.

The signal recognition particle (SRP) binds to ribosomes that synthesize nascent chains bearing signal sequences and catalyzes their targeting to the endoplasmic reticulum membrane. In S. cerevisiae, a temperature-sensitive mutation in the SEC65 gene, encoding an SRP subunit, results in lowered levels of SRP. Growth and protein translocation defects induced by this mutation can be suppressed specifically by sublethal doses of cycloheximide but not anisomycin, each inhibitors of different steps of translation elongation. Cycloheximide also suppresses protein translocation defects caused by depletion of a different SRP subunit. We propose that reduced elongation rates in the presence of cycloheximide allow otherwise insufficient SRP to interact efficiently with ribosomes. These results are consistent with a sampling model in which SRP cycles on and off of translating ribosomes at specific steps during the elongation cycle to inspect all nascent chains for the presence of signal sequences.

Animals↗

PubMed1995

An amino-terminal domain containing hydrophobic and hydrophilic sequences binds the signal recognition particle receptor alpha subunit to the beta subunit on the endoplasmic reticulum membrane.

The signal recognition particle receptor consists of two subunits of 72 kDa (SR alpha) and 30 kDa (SR beta). Assembly of SR alpha on the endoplasmic reticulum membrane can occur independent of the signal recognition particle-mediated translocation pathway. To identify the sequences within SR alpha necessary for membrane binding, a series of amino-terminal and internal deletion mutants was constructed and translated in a cell-free system. In addition, nascent SR alpha polypeptides of varying lengths were generated by cycloheximide treatment of translation reactions. Microsome binding assays performed on these polypeptides revealed a membrane binding domain consisting of the amino-terminal 140 residues of SR alpha. This domain includes the two hydrophobic sequences originally proposed to bind to membranes and a highly charged region not previously implicated in membrane assembly. Furthermore, the domain forms a protease-resistant folding unit that after proteolysis can target and anchor onto microsomes. Extraction of microsomal SR alpha at high pH supplemented with 1 M NaSCN suggests that SR alpha and the membrane binding domain are not integrated in the endoplasmic reticulum membrane. The membrane binding domain is also the major site of tight binding with SR beta, suggesting that SR beta plays a role in the membrane assembly of SR alpha.

Amino Acid Sequence↗

PubMed1995

The presence of a D-stem but not a T-stem is essential for triggering aminoacylation upon anticodon binding in yeast methionine tRNA.

Dissection of the yeast cytoplasmic initiator tRNA(Met) into two helical domains, the T psi C acceptor and anticodon minihelices, failed to show anminoacylation and binding of the acceptor minihelix by the yeast methionyl-tRNA synthetase (MetRS) even in the presence of the anticodon minihelix. In contrast, based on the measure of the inhibition constant Ki, the anticodon minihelix carrying the methionine anticodon CAU is specifically bound to the synthetase and with an affinity comparable to that of the full-length tRNA. The yeast tRNA(Met) acceptor and anticodon minihelices were covalently linked using the central core sequences of either bovine mitochondrial tRNA(Ser) (AGY) lacking a D-stem or initiator tRNA(Met) from Caenorhabditis elegans lacking a T-stem. Based on modeling studies of analogous constructs performed by others, we assume that the folding and distance between the anticodon and acceptor ends of these hybrid tRNAs are identical to that of canonical tRNA. The three-quarter molecule, which includes the T-stem, has aminoacylation activity significantly more than an acceptor minihelix, while the acceptor stem/anticodon-D stem biloop has near wild-type aminoacylation activity. These results suggest that the high selectivity of the anticodon bases in tRNA(Met) depends upon the tRNA L-shape conformation and the presence of a D-arm. Protein contacts with the D-arm phosphate backbone are required for connecting anticodon recognition with the active site. These interactions probably contribute to fine tune the position of the acceptor end in the active site, allowing entry into the transition state of aminoacylation upon anticodon binding. The importance of an L structure for recognition of tRNA(Met) by yeast MetRS was also deduced from mutations of tertiary interactions known to play a general role in tRNA folding.

Acylation↗

PubMed1995

Oxidants in mitochondria: from physiology to diseases.

Reactive oxygen species (ROS: superoxide radical, O2.-; hydrogen peroxide, H2O2; hydroxyl radical, OH.), which arise from the univalent reduction of dioxygen are formed in mitochondria. We summarize here results which indicate that ROS, and also the radical nitrogen monoxide ('nitric oxide', NO), act as physiological modulators of some mitochondrial functions, but may also damage mitochondria. Hydrogen peroxide, which originates in mitochondria predominantly from the dismutation of superoxide, causes oxidation of mitochondrial pyridine nucleotides and thereby stimulates a specific Ca2+ release from intact mitochondria. This release is prevented by cyclosporin A (CSA). Hydrogen peroxide thus contributes to the maintenance of cellular Ca2+ homeostasis. A stimulation of mitochondrial ROS production followed by an enhanced Ca2+ release and re uptake (Ca2+ 'cycling') by mitochondria causes apoptosis and necrosis, and contributes to hypoxia/reperfusion injury. These kinds of cell injury can be attenuated at the mitochondrial level by CSA. When ROS are produced in excessive amounts in mitochondria nucleic acids, proteins, and lipids are extensively modified by oxidation. Physiological (sub-micromolar) concentrations of NO potently and reversibly deenergize mitochondria at oxygen tensions that prevail in cells by transiently binding to cytochrome oxidase. This is paralleled by mitochondrial Ca2+ release and uptake. Higher NO concentrations or prolonged exposure of cells to NO causes their death. It is concluded that ROS and NO are important physiological reactants in mitochondria and become toxic only when present in excessive amounts.

Animals↗

PubMed1995

The 70 carboxyl-terminal amino acids of nascent secretory proteins are protected from proteolysis by the ribosome and the protein translocation apparatus of the endoplasmic reticulum membrane.

We have used proteolysis to examine the environment through which nascent secretory proteins are translocated across the membrane of the endoplasmic reticulum. After solubilization of rough microsomes with detergent, fragments comprised of the approximately 70 carboxyl-terminal amino acids of translocating nascent chains initiated and targeted in vivo were protected from digestion by added proteases. About 40 amino acids of nascent chains were protected from proteolysis by the ribosome; thus, membrane-derived components protect an additional 30 amino acids. Under conditions in which those 30 additional amino acids are protected, only a small set of integral membrane proteins remained associated with the ribosome. These proteins include the Sec61 complex previously identified as the core component of the membrane-bound protein translocation apparatus. These results support the concept of a translocation pore that makes intimate contact with the ribosome and thereby protects nascent chains from proteolytic digestion for an additional, constant length.

Animals↗

PubMed1995

Alteration of pulmonary macrophage function by respiratory syncytial virus infection in vitro.

Alveolar macrophages (AL) are the first line of defense against inhaled pathogens and are exposed to virus during the course of a respiratory syncytial virus (RSV) infection. Interference of virus with alveolar macrophage functions may contribute to the risk of acquiring secondary bacterial infections during or after respiratory tract infections with RSV or other viral agents. We studied whether murine AL get infected with RSV and whether they support viral replication in vitro. In addition, the effects of RSV on microbicidal and on immunoregulatory functions were examined. Only a subpopulation of AL expressed viral F proteins after exposure of these cells to RSV. Infected AL released only small amounts of infectious virus into the supernatant. The extent of virus replication in AL seemed to be dependent in part on the amount of IFN induced by the virus, as has been demonstrated by infection of lung tissue macrophages and AL in vitro. In general, RSV infection of pulmonary macrophages appeared to be abortive. Nevertheless, release of reactive oxygen intermediates, phagocytosis, and killing of protozoa were reduced in RSV-infected AL in comparison to noninfected AL. In contrast, RSV stimulated secretion of TNF-alpha, IL-1, and IL-6 in an infectious-dose dependent manner. Along with the increased cytokine release, accessory functions of AL were increased after RSV exposure. Thus, exposure of AL to RSV appeared to stimulate their immunoregulatory functions, whereas the microbicidal activity of these cells seemed to be severely diminished.

Animals↗

PubMed1995

Electrophysiologic abnormalities in two cases of familial amyloidosis.

PURPOSE/METHODS: We recorded electrophysiologic data of two patients with familial amyloidosis. RESULTS/CONCLUSIONS: Only minor abnormalities could be demonstrated clinically and by means of fluorescein angiography in one patient. Considerable alterations of electrophysiologic responses could be found in both patients. These results suggest that an early retinal or optic nerve involvement in amyloidosis could be detected by using these noninvasive techniques.

Adult↗