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T Frey

Publications and source records attributed to T Frey.

At least 19 recordsLinked to original sources
PubMed2000

Evidence for phase-separated quantum dots in cubic InGaN layers from resonant raman scattering

The emission of light in the blue-green region from cubic InxGa1-xN alloys grown by molecular beam epitaxy is observed at room temperature and 30 K. By using selective resonant Raman spectroscopy (RRS) we demonstrate that the emission is due to quantum confinement effects taking place in phase-separated In-rich quantum dots formed in the layers. RRS data show that the In content of the dots fluctuates across the volume of the layers. We find that dot size and alloy fluctuation determine the emission wavelengths.

Journal Article↗
PubMed1999

Nifedipine is not feasible for biliary pain in patients with gallbladder stones.

OBJECTIVE: Biliary pain is generally treated with NSAIDs and spasmolytics, but some patients do not tolerate them. Nifedipine has been suggested to have some analgesic effect and it has been used successfully in many painful smooth muscle disorders. Our aim was to evaluate the effect of nifedipine for biliary colics and gallbladder volume. PATIENTS AND METHODS: Twenty-seven patients suffering from uncomplicated symptomatic gallbladder stones were prospectively randomized to receive either oral nifedipine (10 mg 3 times daily) or placebo in a double-blind manner. Liver chemistry and ultrasonography were examined before and after the 8-week study period. The patients completed each day a diary of their pain, headache, palpitation, burning feeling in skin, dizziness, and their use of painkillers. RESULTS: Biliary pain seemed to be less intensive and shorter in duration, but without statistical significance, whereas headache tended to be more common (p = 0.077) in nifedipine group than that in placebo group. This difference would have reached statistical significance with over 155 patients randomized. Overall additional drug use was similar in both groups, and was increased in nifedipine group for headache (p = 0.05). The fasting gallbladder volume tended to decrease (p = 0.085) during the nifedipine treatment but not with placebo. Serum liver chemistry remained within normal range. CONCLUSIONS: This small study shows that nifedipine may decrease slightly biliary pain intensity and duration, and contrary to previous findings in healthy volunteers, it seems to decrease resting gallbladder volume in patients with symptomatic uncomplicated gallbladder stones, but did not reduce the need of traditional pain medication partly because of increased need for headache. Thus it is not a feasible choice for routine use against biliary pain in symptomatic gallbladder stones, which is why the study was not continued to reach statistical significance in respect to biliary pain.

Adult↗
PubMed1997

Correlated flow cytometric analysis of terminal events in apoptosis reveals the absence of some changes in some model systems.

Many parallel processes occur during the final stages of apoptosis. It is not clear which of these processes occur in all or most models of apoptosis and which occur only in some. In addition, the temporal relationship of these events is not always well understood. Correlated flow cytometric measurements were used to address these questions. Several models of apoptosis were studied, including thymocytes treated with dexamethasone. MOLT-4 cells treated with etoposide, U937 cells treated with anti-Fas, HL-60 cells treated with camptothecin, Raji cells grown in low serum, and aged neutrophils. All models showed a decrease in LDS-751 and fluorescein diacetate (FDA) staining, an increase in staining with dihydrorhodamine 123 (dhR123) or dihydroethidium, and an acidification of the cytoplasm. In each model, these changes were highly correlated, appearing simultaneously as multiparameter measurements. Changes in membrane status detected with merocyanin 540 (MC540) and annexin V behaved differently. A population with LDS-751 and FDA changes but without annexin V or MC540 changes could be demonstrated in some models. Several models did not show any change in annexin V binding, and HL-60 did not show a change in MC540 binding during apoptosis. The loss of cell surface antigens (CD45 and CD16) from aged neutrophils occurred in the entire LDS-751 and FDA dim population, even though other membrane changes (including the appearance of annexin V binding sites) were only apparent in a subset of these cells. These results suggest a model for the ordering of some of the terminal processes in apoptosis, with annexin V and MC540 changes trailing other events in apoptosis. These results confirm the need for caution in using a single-parameter measurement as an indicator of apoptosis for any new model being studied.

Animals↗
PubMed1997

Electron tomography of neuronal mitochondria: three-dimensional structure and organization of cristae and membrane contacts.

The structure of neuronal mitochondria from chick and rat was examined using electron microscope tomography of chemically fixed tissue embedded in plastic and sliced in approximately 500 nm-thick sections. Three-dimensional reconstructions of representative mitochondria were made from single-axis tilt series acquired with an intermediate voltage electron microscope (400 kV). The tilt increment was either 1 degree or 2 degrees ranging from -60 degrees to +60 degrees. The mitochondrial ultrastructure was similar across species and neuronal regions. The outer and inner membranes were each approximately 7 nm thick. The inner boundary membrane was found to lie close to the outer membrane, with a total thickness across both membranes of approximately 22 nm. We discovered that the inner membrane invaginates to form cristae only through narrow, tubular openings, which we call crista junctions. Sometimes the cristae remain tubular throughout their length, but often multiple tubular cristae merge to form lamellar compartments. Punctate regions, approximately 14 nm in diameter, were observed in which the inner and outer membranes appeared in contact (total thickness of both membranes approximately 14 nm). These contact sites are known to a play a key role in the transport of proteins into the mitochondrion. It has been hypothesized that contact sites may be proximal to crista junctions to facilitate transport of proteins destined for the cristae. However, our statistical analyses indicated that contact sites are randomly located with respect to these junctions. In addition, a close association was observed between endoplasmic reticulum membranes and the outer mitochondrial membrane, consistent with the reported mechanism of transport of certain lipids into the mitochondrion.

Animals↗
PubMed1996

Apoptosis of cells in aged samples as detected by the ProCOUNT reagent.

An unusual population of high side scatter, low nucleic acid dye binding, dim CD45 cells was found in aged blood samples stained with the ProCOUNT reagent. Cell surface staining showed that these cells have the surface phenotype of neutrophils. However, they have decreased expression of several surface antigens, bind annexin V, and stain more dimly than normal neutrophils with LDS-751. These characteristics indicate that the cells have become apoptotic. The decreased expression of the CD45 antigen on apoptotic neutrophils could have an impact on some methods for enumerating CD34-positive progenitor cells. Absolute CD34-positive cell counts are frequently obtained by multiplying CD34-positive cells as a percentage of the total cells by the white blood cell count from a hematologyanalyzer. Cells staining dimly with CD45 may not pass a flow cytometer threshold set on this parameter but appear to be detected by a hematology instrument thresholding on cell size. Thus the white blood cell counts from the two sources may not be identical, introducing error into the calculated absolute CD34 count. Absolute counts of CD34 cells based on simultaneous acquisition of a counting bead are not affected by the presence of this population, but purity estimates can be affected if the possible presence of these cells is not considered in aged samples.

Apoptosis↗
PubMed1996

Apoptosis in hematopoietic cells is associated with an extensive decrease in cellular phosphotyrosine content that can be inhibited by the tyrosine phosphatase antagonist pervanadate.

In the present study, we investigated whether apoptosis in hematopoietic cells is associated with changes in cellular phosphotyrosine content. Murine thymocytes and B cells, human leukemia cells, and normal peripheral blood leukocytes were induced to undergo apoptosis by treatment with specific stimuli or by incubation in growth factor-deprived medium. Multiparameter flow cytometry was used to measure changes in phosphotyrosine content that correlated with the appearance of features of programmed cell death, such as cell shrinkage, DNA fragmentation, and loss of membrane integrity. The results show that conditions that induced apoptosis also induced a dramatic decrease in cellular phosphotyrosine levels. Tyrosine dephosphorylation preceded the loss of plasma membrane integrity and, in most cases, was temporally correlated with the onset of DNA fragmentation. The protein tyrosine phosphatase antagonist pervanadate had a dose-dependent inhibitory effect on both dephosphorylation and apoptosis in murine thymocytes, which were treated with dexamethasone or with the topoisomerase II inhibitor etoposide. The results suggest that extensive tyrosine dephosphorylation is an intrinsic part of the apoptotic process of hematopoietic cells and may be involved mechanistically in the apoptosis induced by certain stimuli.

Animals↗
PubMed1995

Nucleic acid dyes for detection of apoptosis in live cells.

Apoptotic thymocytes were found to be much dimmer than normal thymocytes when stained with several nucleic acid dyes. These dyes provide a quick and simple assay for apoptosis which works for live cells and does not require a UV laser. The collection of dyes giving this staining pattern includes reagents suitable for use in either the FL1, FL2, or FL3 channel of a standard FACScan. Cells identified by these reagents were identical to apoptotic thymocytes defined by several widely used criteria: (i) rapid uptake of Hoechst 33342 but exclusion of propidium iodide, (ii) merocyanin 540 bright, and (iii) sub-G1 DNA content when permeabilized in a buffer that elutes fragmented DNA. In addition, L3T4/Thy-1 dim thymocytes were included in the dyc dim population. The standard Hoechst 33342 and merocyanin 540 assays were not able to separate the normal and apoptotic populations in HL-60 cells treated with camptothecin. However, the dyes SYTO-16 and LDS-751 both gave adequate differentiation of apoptotic from nonapoptotic cells in this model system. Some of these dyes also emit very little in other fluorescence channels of the flow cytometer and can be used in multicolor assays on cytometers equipped with only a single argon-ion laser.

Acridine Orange↗
PubMed1995

Dyes providing increased sensitivity in flow-cytometric dye-efflux assays for multidrug resistance.

In an effort to improve detection of P-glycoprotein-mediated multidrug resistance (mdr), several dyes were compared to rhodamine 123 (R123) in efflux assays. Two dyes (SY-38 and SY-3150) were found that provided better sensitivity. These dyes were effluxed by a cell line known to be mdr-positive (P388/R84) but not by an mdr-negative cell line (P388). Efflux was blocked by both verapamil and cyclosporine A. Efflux from KG1a cells was less than from P388/R84, just as has been seen with R123 and daunomycin. In further experiments, a model system was used to demonstrate two-color immunofluorescence plus efflux measurements. This was done using a sequential staining method. A procedure was devised that, at least for this model system, allowed single-step staining with both dye and antibody. The sensitivity of the efflux measurement was slightly compromised by using this one-step staining method.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

Detection of bromodeoxyuridine incorporation by alteration of the fluorescence emission from nucleic acid binding dyes using only an argon ion laser.

A method was developed that uses paired DNA dyes to detect the incorporation of bromodeoxyuridine (BrdUrd) into cellular DNA and requires only 488 nm excitation. The fluorescence of thiazole blue, TO-PRO-3, and LDS-751 was found to be enhanced by the presence of BrdUrd in DNA. Pairing LDS-751, thiazole blue, or TO-PRO-3 with propidium iodide (PI) for flow cytometry allowed the differentiation of cells containing BrdUrd from BrdUrd unlabeled cells. LDS-751 can be excited directly at 488 nm, and TO-PRO-3 or thiazole blue can be excited indirectly by resonance energy transfer from PI. The enhancement of fluorescence from these dyes is correlated with a decrease in PI fluorescence, suggesting an increased energy transfer from PI to the red emitting dye. Fluorescence from other dyes, including thiazole orange, TO-PRO-1, rhodamine 800, oxazine 750, and 7-aminoactinomycin D, was not altered by the presence of BrdUrd in DNA. Results also were obtained showing that BrdUrd detection using PI and TO-PRO-3 is compatible with immunofluorescence staining with FITC-labeled antibodies.

Bromodeoxyuridine↗
PubMed1994

Maintenance of transplantation potential in ex vivo expanded CD34(+)-selected human peripheral blood progenitor cells.

CD34(+)-selected hematopoietic progenitor cells are being increasingly used for autotransplantation, and recent evidence indicates that these cells can be expanded ex vivo. Of 15 patients with solid tumors undergoing a phase I/II clinical trial using CD34(+)-selected peripheral blood progenitor cells (PBPCs) after high-dose chemotherapy, we analyzed the frequency of long-term culture-initiating cells (LTCIC) as a measure of transplantation potential before and after ex vivo expansion of CD34+ cells. PBPCs were mobilized by combination chemotherapy and granulocyte colony-stimulating factor (G-CSF). The original unseparated leukapheresis preparations, the CD34(+)-enriched transplants, as well as nonabsorbed fractions eluting from the CD34 immunoaffinity columns (Ceprate; CellPro, Bothell, WA) were monitored for their capacity to repopulate irradiated allogeneic stroma in human long-term bone marrow cultures. We found preservation of more than three quarters of fully functional LTCIC in the CD34(+)-selected fractions. Quantitation of LTCIC by limiting dilution analysis showed a 53-fold enrichment of LTCIC from 1/9,075 in the unseparated cells to an incidence of 1/169 in the CD34+ fractions. Thus, in a single apheresis, it was possible to harvest a median of 1.65 x 10(4) LTCIC per kg body weight (range, 0.71 to 3.72). In addition, in six patients, large-scale ex vivo expansions were performed using a five-factor cytokine combination consisting of stem cell factor (SCF), interleukin-1 (IL-1), IL-3, IL-6, and erythropoietin (EPO), previously shown to expand committed progenitor cells. LTCIC were preserved, but not expanded during the culture period. Optimization of ex vivo expansion growth factor requirements using limiting dilution assays for LTCIC estimation indicated that the five-factor combination using SCF, IL-1, IL-3, IL-6, and EPO together with autologous plasma was the most reliable combination securing both high progenitor yield and, at the same time, optimal preservation of LTCIC. Our data suggest that ex vivo-expanded CD34+ PBPCs might be able to allow long-term reconstitution of hematopoiesis.

Antigens, CD↗
PubMed1994

Bivariate flow karyotyping with air-cooled lasers.

An experimental flow cytometer was constructed using a quartz flow cell optically coupled to a 1.22 NA lens. A pair of crossed cylindrical quartz lenses allowed multilaser excitation. Two helium-cadmium (HeCd) lasers, emitting 16 mW at 442 nm and 35 mW at 325 nm, were used to excite chromomycin A3 and Hoechst 33258 fluorescence, respectively. Bivariate flow karyotypes from normal human male chromosomes and from the Daudi cell line were obtained and were compared to those from a standard instrument using dual water-cooled lasers. The new experimental instrument exhibited comparable resolution to that from the standard instrument. In further experiments with Daudi chromosomes, the 35 mW HeCd laser was replaced with a 10 mW HeCd laser, and the system still gave good, though slightly decreased, resolution.

Air↗
PubMed1994

Acute pancreatic injury in asymptomatic individuals after heavy drinking over the long-term.

Recently, high-dose short-term alcohol exposure has been observed not to induce acute pancreatic damage, as evaluated by serum pancreatic enzyme activities. In this study the effect of high-dose, long-term alcohol exposure on the pancreas was investigated in 32 consecutive alcoholics admitted to a unit to treat the problems of withdrawal after a long period of heavy drinking. None of the alcoholics complained of abdominal symptoms. The signs of clinical acute pancreatitis (pain, increased serum C-reactive protein concentration or blood white cell count) were not observed in any of the alcoholics. A significant increase in serum total amylase, pancreatic isoamylase and lipase activities developed by the second day after termination of alcohol intake. These enzyme activities remained significantly increased for one week after cessation of drinking. Seven alcoholics had signs of chronic pancreatitis at ultrasonography (pancreatic calcification, pseudocyst). These results suggest that heavy alcohol intake over the long term may frequently induce subclinical pancreatic injury.

Acute Disease↗
PubMed1993

Dimerization of CD4-C kappa chimeric molecules leads to loss of CD4 epitopes.

Structural similarities between two members of the immunoglobulin superfamily were explored by making chimeric immunoglobulin/CD4 antigen molecules. A crossover in the middle of the originally proposed J kappa homology unit of the first domain of the CD4 molecule was used to construct a chimeric molecule having human and mouse CD4 antigen sequence through the first 108 amino acids and murine J kappa and C kappa sequence thereafter. This molecule was expressed in the presence and absence of an immunoglobulin heavy chain. The resulting proteins were assayed for the expression of CD4 epitopes that should be present based on epitope mapping data. Monomeric, homodimeric, and heavy chain/light chain tetrameric forms of the recombinant protein were secreted and were all detectable with anti-kappa reagents. CD4 antibodies precipitated only the form of the CD4-C kappa light chain protein which appears as a monomer by polyacrylamide gel electrophoresis. Neither the homodimer nor the heavy chain/light chain tetramer were detected with CD4 monoclonal antibodies. An engineered gene having this CD4 antigen first domain joined to the human IgG1 constant region, when coexpressed with a mouse lambda light chain, also failed to express detectable CD4 epitopes. The structural implications of the presence or absence of CD4 epitopes on these proteins is discussed.

Animals↗