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Biomedical subjects

P Walter

Publications and source records attributed to P Walter.

At least 163 records · Page 9Linked to original sources
PubMed1995

[Intraocular silicone lenses and silicone oil].

BACKGROUND: Foldable silicone intraocular implants are becoming more popular in conjunction with small incision phacoemulsification. PATIENTS: We observed three patients with silicone oil droplets adherent to the posterior surface of the silicone implant, following silicone oil removal after preceding vitreoretinal surgery with the installation of silicone oil. These droplets could not be dislodged intraoperatively either with focal aspiration or irrigation. They interfered with the patients subjective visual acuity. For this reason, we performed an exchange of the silicone intraocular implant against a PMMA one-piece lens in all three cases. RESULTS: This procedure resulted in an increase of the visual acuity. The mechanism of adherence between the two silicone polymers is finally not known. CONCLUSIONS: With increased use of implantable silicone intraocular lens and silicone oil this complication may be encountered more frequently. Therefore, implantation of silicone lens in vitreoretinal high risk eyes should avoided.

Aged↗
PubMed1995

The beta subunit of the signal recognition particle receptor is a transmembrane GTPase that anchors the alpha subunit, a peripheral membrane GTPase, to the endoplasmic reticulum membrane.

The signal recognition particle receptor (SR) is required for the cotranslational targeting of both secretory and membrane proteins to the endoplasmic reticulum (ER) membrane. During targeting, the SR interacts with the signal recognition particle (SRP) which is bound to the signal sequence of the nascent protein chain. This interaction catalyzes the GTP-dependent transfer of the nascent chain from SRP to the protein translocation apparatus in the ER membrane. The SR is a heterodimeric protein comprised of a 69-kD subunit (SR alpha) and a 30-kD subunit (SR beta) which are associated with the ER membrane in an unknown manner. SR alpha and the 54-kD subunits of SRP (SRP54) each contain related GTPase domains which are required for SR and SRP function. Molecular cloning and sequencing of a cDNA encoding SR beta revealed that SR beta is a transmembrane protein and, like SR alpha and SRP54, is a member of the GTPase superfamily. Although SR beta defines its own GTPase subfamily, it is distantly related to ARF and Sar1. Using UV cross-linking, we confirm that SR beta binds GTP specifically. Proteolytic digestion experiments show that SR alpha is required for the interaction of SRP with SR. SR alpha appears to be peripherally associated with the ER membrane, and we suggest that SR beta, as an integral membrane protein, mediates the membrane association of SR alpha. The discovery of its guanine nucleotide-binding domain, however, makes it likely that its role is more complex than that of a passive anchor for SR alpha. These findings suggest that a cascade of three directly interacting GTPases functions during protein targeting to the ER membrane.

Amino Acid Sequence↗
PubMed1995

[Atrophic thyroiditis: an unusual course of a Basedow-like variation of Hashimoto disease. Apropos of a case].

This case concerns a 27-year-old man with a very high level of anti-thyroid antibody and pretibial elephantiasis myxedema which developed progressively over several years following subtotal thyroidectomy for << hashitoxicosis >>. Complementary resection of the thyroid stump was performed ; under microscopic examination this stump presented an aspect of atrophic thyroiditis. This unusual development towards atrophic thyroiditis raises the problem of the relations between the various forms autoimmune thyroiditis.

Adult↗
PubMed1995

Change in hemorrheological and biochemical parameters following membrane differential filtration.

INTRODUCTION: The elimination of high molecular weight proteins may have a positive influence on disorders of the microcirculation due to an improvement in rheological parameters. We therefore attempted to evaluate the rheological efficacy of membrane differential filtration (MDF). PATIENTS AND METHODS: Ten patients suffering from macular disease underwent MDF. Rheological and biochemical parameters as well as visual acuity were determined one day before and after therapy: The study aimed at a reduction in plasma viscosity, standardized whole blood viscosity at hematocrit 0.45 and erythrocyte aggregation at hematocrit 0.3. RESULTS: Severe side-effects were not observed. The rheological parameters were significantly reduced. In detail the posttreatment values were reduced as compared to the pretreatment values as follows: plasma viscosity 85%, standardised whole blood viscosity 86% (hematocrit 0.45), erythrocyte aggregation 59% (hematocrit 0.3), total protein 81%, IgG 66%, IgA 59%, IgM 33%, alpha-2-macroglobulin 30%, triglycerides 102%, total cholesterol 47%, VLDL cholesterol 94%, LDL cholesterol 33%, HDL cholesterol 62%. Visual acuity was improved in 7/10 patients. CONCLUSIONS: MDF is a safe and highly effective method for lowering biochemical and improving rheological parameters which led to improvement in visual acuity. We have already replaced plasma exchange with MDF in our clinical practice of hemorrheological therapy.

Aged↗
PubMed1994

Subunits of the Saccharomyces cerevisiae signal recognition particle required for its functional expression.

The signal recognition particle (SRP) is an evolutionarily conserved ribonucleoprotein (RNP) complex that functions in protein targeting to the endoplasmic reticulum (ER) membrane. Only two protein subunits of the SRP, Srp54p and Sec65p, and the RNA subunit, scR1, were previously known in the yeast Saccharomyces cerevisiae. Purification of yeast SRP by immunoaffinity chromatography revealed five additional proteins. Amino acid sequencing and cloning of the genes encoding four of these proteins demonstrated that the yeast SRP contains homologs (termed Srp14p, Srp68p and Srp72p) of the SRP14, SRP68 and SRP72 subunits found in mammalian SRP. The yeast SRP also contains a 21 kDa protein (termed Srp21p) that is not homologous to any protein in mammalian SRP. An additional 7 kDa protein may correspond to the mammalian SRP9. Disruption of any one of the four genes encoding the newly identified SRP proteins results in slow cell growth and inefficient protein translocation across the ER membrane. These phenotypes are indistinguishable from those resulting from the disruption of genes encoding SRP components identified previously. These data indicate that a lack of any of the analyzed SRP components results in loss of SRP function. ScR1 RNA and SRP proteins are at reduced levels in cells lacking any one of the newly identified proteins. In contrast, SRP components are present at near wild type levels and SRP subparticles are present in cells lacking either Srp54p or Sec65p. Thus Srp14p, Srp21p, Srp68p and Srp72p, but not Sec65p or Srp54p, are required for stable expression of the yeast SRP.

Amino Acid Sequence↗
PubMed1994

Genetic and biochemical analysis of the fission yeast ribonucleoprotein particle containing a homolog of Srp54p.

Mammalian signal recognition particle (SRP), a complex of six polypeptides and one 7SL RNA molecule, is required for targeting nascent presecretory proteins to the endoplasmic reticulum (ER). Earlier work identified a Schizosaccharomyces pombe homolog of human SRP RNA and showed that it is a component of a particle similar in size and biochemical properties to mammalian SRP. The recent cloning of the gene encoding a fission yeast protein homologous to Srp54p has made possible further characterization of the subunit structure, subcellular distribution, and assembly of fission yeast SRP. S. pombe SRP RNA and Srp54p co-sediment on a sucrose velocity gradient and coimmunoprecipitate, indicating that they reside in the same complex. In vitro assays demonstrate that fission yeast Srp54p binds under stringent conditions to E. coli SRP RNA, which consists essentially of domain IV, but not to the full-length cognate RNA nor to an RNA in which domain III has been deleted in an effort to mirror the structure of bacterial homologs. Moreover, the association of S. pombe Srp54p with SRP RNA in vivo is disrupted by conditional mutations not only in domain IV, which contains its binding site, but in domains I and III, suggesting that the particle may assemble cooperatively. The growth defects conferred by mutations throughout SRP RNA can be suppressed by overexpression of Srp54p, and the degree to which growth is restored correlates inversely with the severity of the reduction in protein binding. Conditional mutations in SRP RNA also reduce its sedimentation with the ribosome/membrane pellet during cell fractionation. Finally, immunoprecipitation under native conditions of an SRP-enriched fraction from [35S]-labeled fission yeast cells suggests that five additional polypeptides are complexed with Srp54p; each of these proteins is similar in size to a constituent of mammalian SRP, implying that the subunit structure of this ribonucleoprotein is conserved over vast evolutionary distances.

Base Sequence↗
PubMed1994

Interaction of E. coli Ffh/4.5S ribonucleoprotein and FtsY mimics that of mammalian signal recognition particle and its receptor.

The mechanism of protein translocation across the endoplasmic reticulum membrane of eukaryotic cells and the plasma membrane of prokaryotic cells are thought to be evolutionarily related. Protein targeting to the eukaryotic translocation apparatus is mediated by the signal recognition particle (SRP), a cytosolic ribonucleoprotein, and the SRP receptor, an endoplasmic reticulum membrane protein. During targeting, the 54K SRP subunit (M(r) 54,000; SRP54), a GTP-binding protein, binds to signal sequences and then interacts with the alpha-subunit of the SRP receptor (SR alpha), another GTP-binding protein. Two proteins from Escherichia coli, Ffh and FTsY, structurally resemble SRP54 and SR alpha. Like SRP54, Ffh is a subunit of a cytosolic ribonucleoprotein that also contains the E. coli 4.5S RNA. Although there is genetic and biochemical evidence that the E. coli Ffh/4.5S ribonucleoprotein has an SRP-like function, there is no evidence for an SR alpha-like role for FtsY. Here we show that the Ffh/4.5S ribonucleoprotein binds tightly to FtsY in a GTP-dependent manner. This interaction results in the stimulation of GTP hydrolysis which can be inhibited by synthetic signal peptides. These properties mimic those of mammalian SRP and its receptor, suggesting that the E. coli Ffh/4.5S ribonucleoprotein and FtsY have functions in protein targeting that are similar to those of their mammalian counterparts.

Amino Acid Sequence↗
PubMed1994

[Pseudo-aneurysm of the hepatic artery. A rare complication after laparoscopic cholecystectomy].

With the spread of laparoscopic cholecystectomy more and more complications are being reported. For the first time in this paper a pseudoaneurysm of the right hepatic artery as a complication of laparoscopic cholecystectomy in a 55 year old patient is described. During embolization the aneurysm ruptured and an emergency laparotomy was performed. The right hepatic artery was ligated. The postoperative course up to follow-up at 6 months was uncomplicated.

Aneurysm, False↗
PubMed1994

Identification of fast spurts of pyridine nucleotide oxidation evoked by light stimulation in the isolated perfused vertebrate retina.

Transitory increases of ultraviolet transmission on stimulation with light were recorded simultaneously with electroretinogram on and off effects from isolated vertebrate retina. The spectral distribution of the optical light responses coincided with that of NADH reduction. The correlation of the optical, or respiratory, responses and the electrical responses were very close within a wide range of stimulus parameters, suggesting an interpretation in terms of supply and demand of energy with a tight coupling between the two kinds of evoked activity. Prerequisite to the response behaviour was the preservation of synaptic signal transmission from first- to higher-order retinal neurons.

Animals↗
PubMed1994

Protein translocation across the endoplasmic reticulum.

In the past year, dramatic progress has been made in our understanding of protein biogenesis at the initial steps of the eukaryotic secretory pathway. New insights have refined our view of protein targeting to the endoplasmic reticulum membrane and provided the best glimpse so far of the subsequent translocation step. The interactions of three GTP-binding proteins have been found to result in a novel cycle of GTP binding and hydrolysis to regulate protein targeting. Experiments with fluorescent probes have revealed that the nascent chain enters an aqueous environment within the membrane sealed off from the cytosol. In vitro reconstitution experiments have shown surprising simplicity in the number of polypeptides required to facilitate translocation across a synthetic membrane and to promote the integration of membrane proteins. Furthermore, new genetic and functional similarities between divergent organisms have been discovered, providing convincing evidence of the evolutionary conservation of strategies used in the targeting and translocation of polypeptides.

Animals↗
PubMed1994

The unfolded-protein-response pathway in yeast.

The accumulation of unfolded proteins in the endoplasmic reticulum (ER) triggers the increased production of several ER-resident proteins. This signalling pathway exists in organisms as divergent as mammals and yeast, and is the only known example of an intracellular signalling system that links the ER and the nucleus. Recently, a transmembrane kinase similar in structure to growth-factor receptor kinases has been identified as a key component of the unfolded-protein-response pathway in yeast.

Journal Article↗
PubMed1994

Pretreatment with methylprednisolone in coronary artery bypass grafting influences the levels of histamine and tryptase in serum but not in bronchoalveolar lavage fluid.

1. The presence of histamine and tryptase in serum during and after coronary artery bypass grafting may be an indication of the induction of inflammation. 2. One group of patients received no glucocorticoids and a second group received methylprednisolone before extracorporeal circulation. In the steroid group no effects were seen on the basal levels of histamine (2.84 +/- 0.12 ng/ml) and tryptase (0.50 +/- 0.05 ng/ml) during and after surgery. In the other group two peak levels of histamine were observed: one at 10 min after starting extracorporeal circulation (4.19 +/- 1.79 ng/ml) and another at 4 h after surgery (8.26 +/- 4.85 ng/ml). In this group tryptase was only elevated during the period of extracorporeal circulation (1.54 +/- 0.16 ng/ml). 3. There were no differences between the two groups in complement activation. C3a levels rose to 170 +/- 8% and 180 +/- 10% of the initial value in the steroid and non-steroid group, respectively. 4. It was concluded that during surgery mast cells were activated, but since tryptase levels decreased in the post-operative period, the second increase in the histamine level can be explained by activation of basophils or by an unknown mechanism for the release of histamine but not tryptase by mast cells. 5. In the bronchoalveolar lavage fluid the levels of histamine and tryptase showed no differences between the two groups of patients, but histamine was enhanced compared with normal levels.

Bronchoalveolar Lavage Fluid↗
PubMed1994

[Digital data collection and analysis in clinical electrophysiology. A PC program for electrophysiology].

BACKGROUND: The number of data acquired in electrophysiology and the need for immediate analysis and interpretation justified the use of computerized signal acquisition and -analysis. Since such techniques are well known and established in computerized perimetry, the user of EOG, ERG, and VEP will profit from such an approach. METHOD: A computer program for signal acquisition and -analysis of clinical electrophysiology is described. The software is written in BASIC for IBM compatible PC/XT/AT computers. The program supports all electrophysiological examinations (EOG, ERG, VEP). It contains a subroutine for automated EOG recording and -analysis, allows measurements of amplitude and latency of standardized Ganzfeld-ERG and pattern-ERG. Options for recording and analysis of further stimuli are prepared. The possibility of determination of area under the curve is implemented. In the VEP subroutine evaluation of amplitude, latency, area under the curve, and Fast-Fourier-Transformation--necessary for steady-state-VEP--is installed. CONCLUSION: The program demonstrates that with the now available low cost Personal Computer technology it is possible to build up individual software systems for clinical electrophysiology supporting and optimizing all recording, analysing, and administrative procedures.

Data Collection↗
PubMed1994

Dietary components of malt extract such as maltodextrins, proteins and inorganic salts have distinct effects on glucose uptake and glycogen concentrations in rats.

As shown previously, glycogen deposition in liver and muscle is significantly greater in rats fed a diet containing barley malt extract than in those fed diets containing glucose or starch. We investigated whether particular components of malt extract (glucose oligomers, inorganic salts, protein) were responsible for this effect. Food-deprived rats were fed diets containing carbohydrates of different chain lengths [glucose, maltose, maltodextrins or malt carbohydrates (84-86 g/100 g)] in the presence and absence of inorganic salts (2 g/100 g) and maltodextrin diets (78 g/100 g) containing either no protein or 20 g casein/100 g. Dietary glucose oligomers caused higher blood glucose concentrations than consumption of glucose or maltose but had no significant influence on liver or muscle glycogen. Salt addition resulted in higher muscle glycogen concentrations but had no effect on blood glucose or liver glycogen. Hepatic glycogen concentrations were significantly greater in rats fed casein compared with those fed no protein. We propose that consumption of malt extract has the following advantages over consumption of diets containing glucose or maltose: 1) better glucose absorption related to the presence of glucose oligomers, 2) greater hepatic glycogen concentrations associated with the protein in malt extract, and 3) greater glycogen concentrations in muscle due to the presence of inorganic salts.

Animals↗
PubMed1994

Perioperative complications of cardioverter-defibrillator implantation: the Emory experience.

Over a 5-year period, 110 cardioverter-defibrillators (109 epicardial, 1 transvenous) were implanted consecutively in selected patients with ventricular tachyarrhythmias. The perioperative course of this patient population was examined to determine the associated morbidity and mortality of the procedure. Patients were predominantly male, with coronary artery disease and a decreased left ventricular ejection fraction. Most underwent median sternotomy for implantable cardioverter defibrillator implantation. The incidence of perioperative mortality was found to be 2.7%. New-onset atrial fibrillation or flutter occurred in 17.3% of the patients during the postoperative period and aggravation of ventricular tachyarrhythmias in 19.1%. The ICD system became infected in 2.7% of the patients and the mediastinal incision site infected in 2.4%. Pneumonia developed in 4.5%. Other complications included significant blood loss, ICD pocket hematomas, and lead dislodgement. There is an appreciable incidence of morbidity and mortality associated with ICD implantation.

Adult↗