Biomedical subjects

G J Koper

Publications and source records attributed to G J Koper.

7 recordsLinked to original sources

PubMed1997

On the difference in ionization properties between planar interfaces and linear polyelectrolytes.

Ionizable planar interfaces and linear polyelectrolytes show markedly different proton-binding behavior. Planar interfaces protonate in a single broad step, whereas polyelectrolytes mostly undergo a two-step protonation. Such contrasting behavior is explained using a discrete-charge Ising model. This model is based on an approximation of the ionizable groups by point charges that are treated within a linearized Poisson-Boltzmann approximation. The underlying reason as to why planar interfaces exhibit mean-field-like behavior, whereas linear polyelectrolytes usually do not, is related to the range of the site-site interaction potential. For a planar interface, this interaction potential is much more long ranged if compared with that of the cylindrical geometry as appropriate to a linear polyelectrolyte. The model results are in semi-quantitative agreement with experimental data for fatty-acid monolayers, water-oxide interfaces, and various linear polyelectrolytes.

Electrolytes↗

PubMed1986

Measurement of single-cell DNA synthesis by pokeweed mitogen-stimulated mononuclear cells with combined light and scanning electron microscopy.

The response of peripheral blood mononuclear cells to pokeweed mitogen (PWM) stimulation was investigated with combined light (LM) and scanning electron microscopy (SEM). The DNA content of the nucleus of a cell (measured by fluorescence) was compared directly with the diameter and morphological features (by SEM). It was found that upon PWM stimulation lymphocytes transform into blast cells without measurable increase of diploid DNA content (4C) were not seen. The results of DNA fluorescence measurements were comparable with [3H]thymidine uptake profiles, both having peak values on Days 4 and 5 after the start of stimulation. Lymphocyte-enriched populations stimulated by PWM showed a small but distinct population of cells with a diameter of approximately 4-5 micrometers and having a tetraploid DNA content on Days 3, 4 and 5 after the start of stimulation. This reflects the cells' ability to divide in response to mitogen stimulation. SEM showed no characteristic cell-surface morphology for blast cells with increasing DNA content.

DNA↗

PubMed1983

Flow cytometry of reticulocytes applied to clinical hematology.

Reticulocytes in fixed human blood samples were stained for RNA with the fluorescent dye pyronin Y and measured by flow cytometry. The resulting relative frequency distributions of the RNA fluorescence intensities concurred with the different stages in maturation from early reticulocytes to mature red cells. A computer program was written to calculate from these frequency distributions the relative number of reticulocytes, their relative RNA content, and the median of the reticulocyte population (RNA index). This method was applied to 30 healthy blood bank donors (control group), as well as to patients with various hematologic disorders showing abnormal erythropoietic activity. The measured percentage of reticulocytes, RNA content, and RNA index were found to correlate well with the various hematologic disorders. Changes in erythropoiesis could be clearly followed, as was demonstrated by analyzing blood samples from children with aplastic anemia or acute myeloid leukemia, who were treated with allogeneic bone marrow transplantation. Measurements on blood samples from healthy blood bank donors showed that with this method, small changes in the reticulocyte population, such as the appearance of polychromatic erythrocytes in the peripheral blood 5-8 hr after donation, can be detected. The statistical reliability and the information provided on the maturation stage of the entire reticulocyte population make flow cytometry of peripheral blood reticulocytes a more informative method for the study of hematologic abnormalities than conventional methods for reticulocyte counting and classification.

Anemia, Aplastic↗

PubMed1982

An epiiluminator/detector unit permitting arc lamp illumination for fluorescence activated cell sorters.

The application of arc lamps to flow cytometers is discussed and epiillumination for jet-in-air cell sorters is introduced. An epiilluminator/detector unit equipped with a mercury arc lamp constructed for a commercially available cell sorter is described. Experiments in which laser and mercury arc lamp illumination were compared show that the signal-to-noise ratio for the arc lamp illumination is predominantly limited by shot noise from constant light backgrounds due to reflected excitation light and ambient light. Arc lamp illumination can be used for the sorting of highly fluorescent objects such as cells stained for DNA by for example: ethidium bromide, propidium iodide, or the Hoechst dyes. The simultaneous employment of mercury arc and laser light sources as an inexpensive dual wavelength system is discussed.

Cell Separation↗

PubMed1981

Flow cytometry of human reticulocytes based on RNA fluorescence.

A fluorescent staining procedure based on pyronin Y is described. The technique has been used to stain RNA in human reticulocytes for subsequent flow analysis and sorting. Histograms of fluorescence values of mature red blood cells and reticulocytes obtained by flow cytometry of stained blood samples, contain more information than offered by conventional methods for counting reticulocytes. Analysis of the fluorescence histograms provides new descriptive parameters of the reticulocyte populations. The potential importance of this method in experimental and routine hematology is illustrated for a number of clinical cases.

Anemia↗

PubMed1981

The look-up table: a classifier for cell sorters.

Currently used classifiers for flow cell sorters are described and the look-up table is introduced as such. An experimental setup of a look-up table classifier added to a commercially available cell sorter, under control of a microcomputer is described. The contents of the look-up table are obtained from contours of regions of interest. These regions are defined by the user who designates the areas on a video color display of the bivariate flow data. Since most cell clusters form elliptic or ovoid shapes in a multi-dimensional feature space this method enables a better matching of window shapes to cluster outlines, compared to conventional sort decision circuitry.

Cell Separation↗

PubMed1981

The look-up table: a logarithmic converter for cell sorters.

The employment of logarithmic amplifiers for flow cytometers is discussed and a logarithmic conversion algorithm is introduced. Two applications of the algorithm are given: the rescaling of a histogram and the use of a cheap programmable read-only memory circuit. The performance of the algorithm is compared with a logarithmic amplifier.

Cell Separation↗