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Biomedical subjects

R Nossal

Publications and source records attributed to R Nossal.

At least 19 recordsLinked to original sources
PubMed1990

Small angle neutron scattering studies of HbA in concentrated solutions.

Differential cross-sections for neutrons scattered by normal human hemoglobin have been determined over the range of concentrations from 2 to approximately 35 weight percent. Data are compared with structure factors calculated from models of monodisperse hard spheres interacting through a screened Coulomb potential. Good agreement is noted when the volume fraction eta is adjusted during multivariate fitting of data, but the fitted value of eta is always lower than expected from the known Hb concentration of the samples. Calculations of cross-sections for polydisperse scatterers suggest that the samples may contain oligomers of the fundamental tetrameric Hb molecule.

Carboxyhemoglobin↗
PubMed1988

SANS studies of interacting hemoglobin in intact erythrocytes.

Small angle neutron scattering (SANS) was used to investigate interaction forces between hemoglobin (Hb) molecules contained within human red cells. The scattering separately attributable to cell membranes and intracellular Hb was identified. A series of D2O-H2O contrast variation measurements were made in order to establish conditions for which scattering from the cell membrane is minimized (approximately 15% D2O). Measurements then were performed to examine changes in intermolecular Hb interactions occurring when the cells are contracted or swollen by varying the ionic strength of the suspension buffer. The scattering cross-sections were fitted to structure factors computed by a mean spherical approximation, and molecular parameters thereby extracted. Oxygenation studies on normal cells were performed, and results contrasted with those of similar studies of erythrocytes obtained from sickle cell disease patients.

Anemia, Sickle Cell↗
PubMed1988

On the elasticity of cytoskeletal networks.

Models relating to the gelation and elasticity of complex cytoskeletal networks are formulated and investigated. Kinetic equations for reversible elongation of nucleated actin filaments are analyzed when the filaments are acted upon by capping proteins and cross-linking factors. Analytical expressions are obtained that relate the low frequency elastic shear modulus of a network, G, to chain growth kinetics, the number of nucleation sites, monomer concentration, and the amount of capping and cross-linking protein. Elasticity curves that relate G to such factors as the association constant for cross-linking are derived and then used to determine solation-gelation phase contours.

Actins↗
PubMed1988

[Diagnosis and therapy of hyponatremic syndromes].

Hyponatremia is the most common abnormality in electrolyte and water metabolism. In adult patients it is related to high morbidity and mortality. The degree of CNS-damage depends 1st on the absolute serum sodium concentration (NaS) and 2nd on the rapidity with which NaS is lowered. The most frequent etiology of hyponatremia in pediatric patients is dilutional hyponatremia (SIADH, infusion-therapy). Nephrotic syndromes and congestive heart insufficiency associated with cardiac low output are further causes. Being aware of the different pathophysiological mechanism prevention of hyponatremia is easily achieved by monitoring serum electrolytes, water balance and compensating renal factors in critically ill patients. Hyponatremias accompanied by neurological symptoms should be corrected by rapid infusion of hypertonic saline (514 mmol/l). NaS concentration should increase at a rate of 2 mmol/1 hour. Symptoms of central pontine myelinolysis in hyponatremia were not yet described in pediatric patients.

Child↗
PubMed1987

Model for photon migration in turbid biological media.

Various characteristics of photon diffusion in turbid biological media are examined. Applications include the interpretation of data acquired with laser Doppler blood-flow monitors and the design of protocols for therapeutic excitation of tissue chromophores. Incident radiation is assumed to be applied at an interface between a turbid tissue and a transparent medium, and the reemission of photons from that interface is analyzed. Making use of a discrete lattice model, we derive an expression for the joint probability gamma(n, rho)d2 rho that a photon will be emitted in the infinitesimal area d2 rho centered at surface point rho = (x, y), having made n collisions with the tissue. Mathematical expressions are obtained for the intensity distribution of diffuse surface emission, the probability of photon absorption in the interior as a function of depth, and the mean path length of detected photons as a function of the distance between the site of the incident radiation and the location of the detector. We show that the depth dependence of the distribution of photon absorption events can be inferred from measured parameters of the surface emission profile. Results of relevant computer simulations are presented, and illustrative experimental data are shown to be in accord with the theory.

Computer Simulation↗
PubMed1987

Dynamic light scattering methods for biorhelogy.

Several noninvasive light scattering techniques are reviewed that can be utilized in rheological studies of mucus and other soft biological matrices. Included are quasielastic light scattering techniques to determine the compressibility moduli of polymer lattices, resonance methods that can be used to measure the shear modulus of weak gels, assays that probe the swelling and contraction of mucin aggregates, and microscope based light scattering techniques to probe gelation within single cells.

Lasers↗
PubMed1984

Effect of Ca++ on the structure and rheology of canine tracheal mucin.

Mucin glycoproteins are known to be the principal determinants of epithelial mucus rheology and hence of mucociliary transport rates. We are studying the structure of such glycoproteins using a model mucin purified from canine tracheal pouch secretions. Of particular interest is the effect on mucin structure of increased Ca++ such as occurs in certain disease states. Quasielastic laser light scattering was used to study the effect of Ca++ on the hydrodynamic radius of the mucin molecules. Scattering data from 0.3mg/ml mucin solutions in physiological phosphate buffer containing 0, 5 X 10(-5)M, and 5 X 10(-4)M Ca++ were analyzed to obtain an average translational diffusion coefficient and the distribution of molecular radii for the dispersion. The effect of Ca++ was to decrease the average Stokes radius. The light scattering results are supported by rheologic measures of mucin gel viscoelasticity.

Animals↗
PubMed1984

Studies of rheologically active biological macromolecules by quasielastic light scattering.

Variables which describe the structure and rheological behavior of macromolecules in both dilute solutions and gels may be determined using methods of quasielastic laser light scattering (QELS). Such parameters include diffusion coefficients, molecular size such as hydrodynamic radius, and viscoelastic moduli. If the polymer is polydisperse, the distribution of radii may be estimated. Application of the methods is illustrated with data on the size distribution of a tracheal mucin glycoprotein solution as an example of a polydisperse polymer solution of biorheological interest. A scheme for measuring shear moduli of polymer gels using dynamic laser light scattering is illustrated with data on reconstituted fibrin clots.

Animals↗
PubMed1983

Sizes and mass distributions of clathrin-coated vesicles from bovine brain.

Clathrin-coated vesicles obtained from bovine brain have been studied by ultracentrifugation and dynamic light scattering techniques to provide information on their sedimentation and mass distributions and their average diffusion coefficients. "Uncoated" vesicles, obtained by removing the protein coat from coated vesicles, have been similarly characterized. For typical preparations, maximal values of approximately 210 and 95 S are observed for the sedimentation coefficients of coated and uncoated vesicles, respectively. Corresponding values for the average molecular weights, determined from values of average sedimentation and diffusion coefficients, are 49 X 10(6) and 13 X 10(6); values obtained by equilibrium sedimentation are 37.2 X 10(6) and 10.6 X 10(6). In order to obtain these results, some minor modifications of sedimentation and light-scattering techniques have been devised which may have application to other studies of size distributions of large particles.

Animals↗
PubMed1983

Effects of crosslinking on the rigidity and proteolytic susceptibility of human fibrin clots.

Clots formed in reconstituted human plasma or from purified human fibrin were studied in order to assess the effects of subunit crosslinking on clot strength and on resistance to plasmin degradation. The relative amounts of alpha chain and gamma chain ligation were varied by adding factor XIII to the samples. We observe, as have others, that appreciable gamma-gamma crosslinking always precedes detectable formation of alpha dimer or alpha polymer. Non-invasive light scattering measurements of the shear modulus G(t) indicate that ligation of gamma chains and of alpha chains have qualitatively similar effects on clot strength. Since alpha crosslinking occurs very slowly in the clots which are formed from plasma, we infer that under physiological conditions the involvement of alpha chains in the development of clot strength probably is only a secondary function. Light scattering techniques also were used to study the size of particles shed from the surfaces of fibrin clots undergoing fibrinolysis, and no differences could be discerned as resulting from ligation of alpha chains.

Blood Coagulation↗
PubMed1976

Chemotropism indices for polymorphonuclear leukocytes.

Trajectories of polymorphonuclear leukocytes which are responding to a chemical gradient are analyzed in order to deduce probability distributions of the angles between successive path segments. The turn angle probability distributions thus obtained are seen to be strongly dependent on the direction of locomotion prior to a turn, in that cells usually turn to maintain alignment along an axis directed towards the chemoattractant source. A mathematical model based on these observations is developed in order to understand the relationship between net chemotactic response and parameters characterizing stochastic movements of individual cells. In particular, the manner in which the chemotropism index depends on details of the turn-angle distributions is examined. When bias in the direction of turn is induced by a chemotactic field, transition from random motion to directed response occurs most abruptly if the turn-angle distribution is narrow. "Accommodation," viz., a dependence of the mean angle of turn upon prior orientation, is found to have relatively little effect on the magnitude of the response.

Mathematics↗
PubMed1974

Light-scattering spectrum due to wiggling motions of bacteria.

Simple models are used to calculate the inelastic light scattering spectrum of motile bacteria when wiggling motions are included in addition to translational displacement. Computations of spectra lead to the conclusion that nontranslational motions can be neglected when swimming speeds are deduced from light-scattering data for normal vigorously motile strains. On the other hand, for slowly translating bacteria, or for strains exhibiting noticeable wiggling motion when viewed in a microscope, additional spectral components may be significant. Such components are best distinguished when measurements are made at small and intermediate scattering angles; at large angles the spectra have approximately the same scaling properties (functionals of Qt, Q being the Bragg wave vector) as those associated with simple translational motility.

Bacteria↗
PubMed1974

Inelastic light scattering by large structured particles.

Autocorrelation functions are computed for nonspherical particles whose dimensions are comparable to or greater than the wavelength of scattered light. Particular attention is given to models of motile microorganisms. Results for Gaussian ellipsoids, finite thin rods, ellipsoids with internal structures, and dumbbell-shaped scatterers are derived and compared.

Cell Movement↗