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- Light Scattering from Intact Cells Reports Oxidative-Stress-...Light Scattering from Intact Cells Reports Oxidative-Stress-Induced Mitochondrial Swelling
Biophysical Journal, Volume 88, Issue 4, 1 April 2005, Pages 2929-2938
Jeremy D. Wilson, Chad E. Bigelow, David J. Calkins and Thomas H. Foster
AbstractAngularly resolved light scattering measurements were performed on suspensions of EMT6 cells and on mitochondria isolated from rabbit liver. Mie theory analysis of the scattering from intact cells indicated that mitochondrial-sized organelles dominated scattering in the range 5–90°. This interpretation was supported by the analysis of scattering from isolated mitochondria. Intact cells were subjected to oxidative stress by photodynamic insult. After 3h of incubation in the heme precursor aminolevulinic acid hexylester, EMT6 cells accumulated abundant protoporphyrin IX, an endogenous photosensitizer formed in mitochondria. Irradiation of aminolevulinic acid/protoporphyrin IX-sensitized cells with 10J cm of 514nm light led to pronounced changes in angularly resolved light scattering consistent with mitochondrial swelling. Electron microscopy of similarly treated EMT6 cell monolayers showed significant changes in mitochondrial morphology, which included distension of the outer unit membrane and bloating of the internal mitochondrial compartment. Informed by these electron microscopy results, we implemented a coated sphere model to interpret the scattering from intact cells subjected to oxidative stress. The coated sphere interpretation was compatible with the scattering measurements from these cells, whereas simpler Mie theory models based on homogenous swelling were dramatically unsuccessful. Thus, in this system, angularly resolved light scattering reports oxidative-stress-induced changes in mitochondrial morphology.
Abstract | Full Text | PDF (266 kb) - Simulation of Ultrasound Backscattering by Red Cell Aggregat...Simulation of Ultrasound Backscattering by Red Cell Aggregates:Effect of Shear Rate and Anisotropy
Biophysical Journal, Volume 82, Issue 4, 1 April 2002, Pages 1696-1710
Isabelle Fontaine, David Savéry and Guy Cloutier
AbstractTissue characterization using ultrasound (US) scattering allows extraction of relevant cellular biophysical information noninvasively. Characterization of the level of red blood cell (RBC) aggregation is one of the proposed application. In the current paper, it is hypothesized that the microstructure of the RBCs is a main determinant of the US backscattered power. A simulation model was developed to study the effect of various RBC configurations on the backscattered power. It is an iterative dynamical model that considers the effect of the adhesive and repulsive forces between RBCs, and the effect of the flow. The method is shown to be efficient to model polydispersity in size, shape, and orientation of the aggregates due to the flow, and to relate these variations to the US backscattering properties. Three levels of aggregability at shear rates varying between 0.05 and 10s were modeled at 40% hematocrit. The simulated backscattered power increased with a decrease in the shear rate or an increase in the RBC aggregability. Angular dependence of the backscattered power was observed. It is the first attempt to model the US power backscattered by RBC aggregates polydisperse in size and shape due to the shearing of the flow.
Abstract | Full Text | PDF (456 kb) - Red Blood Cells Initiate Leukocyte Rolling in Postcapillary ...Red Blood Cells Initiate Leukocyte Rolling in Postcapillary Expansions: A Lattice Boltzmann Analysis
Biophysical Journal, Volume 85, Issue 1, 1 July 2003, Pages 208-222
Chenghai Sun, Cristiano Migliorini and Lance L. Munn
AbstractLeukocyte rolling on the vascular endothelium requires initial contact between leukocytes circulating in the blood and the vessel wall. Although specific adhesion mechanisms are involved in leukocyte-endothelium interactions, adhesion patterns in vivo suggest other rheological mechanisms also play a role. Previous studies have proposed that the abundance of leukocyte rolling in postcapillary venules is due to interactions between red blood cells (RBCs) and leukocytes as they enter postcapillary expansions, but the details of the fluid dynamics have not been elucidated. We have analyzed the interactions of red and white blood cells as they flow from a capillary into a postcapillary venule using a lattice Boltzmann approach. This technique provides the complete solution of the flow field and quantification of the particle-particle forces in a relevant geometry. Our results show that capillary-postcapillary venule diameter ratio, RBC configuration, and RBC shape are critical determinants of the initiation of cell rolling in postcapillary venules. The model predicts that an optimal configuration of the trailing red blood cells is required to drive the white blood cell to the wall.
Abstract | Full Text | PDF (2905 kb) - …more
Copyright © 1995 The Biophysical Society. All rights reserved.
Biophysical Journal, Volume 69, Issue 3, 1170-1177, 1 September 1995
doi:10.1016/S0006-3495(95)79991-X
Research Article
Measuring diameters of rod-shaped bacteria in vivo with polarized light scattering
B.V. Bronk, S.D. Druger, J. Czégé and W.P. Van de Merwe
U.S. Air Force Project Reliance at ERDEC, Aberdeen Proving Ground, Maryland 21010–5423, USA.
Abstract
The angular function for elements of the Mueller matrix for polarized light scattering from suspensions of microorganisms is known to be reproducible for different growths of a given bacterial strain in the log (or exponential) phase of growth. The reason for this, the stability of the size and shape distribution for cells, is briefly discussed. Experiments were performed using suspensions of two different strains of Escherichia coli cells in log phase and measuring the angular dependence of the Mueller matrix ratio S34/S11. Calculations were then performed using the coupled dipole approximation to model electromagnetic scattering from particles where the shape of an individual cell was approximated by a cylinder capped with hemispheres of the same radius as the cylinder. Using previously measured values for the length distribution and index of refraction of the cells, the calculated scattering curve was found to fit the measured curve very well. The values obtained for the cell diameters were quite close to diameters previously measured by optical microscopy. Thus this method provides a rapid and convenient method for monitoring bacterial diameters in vivo even when there is an appreciable distribution of bacterial lengths in the population.
