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At least 1,639 records · Page 91Linked to original sources
PubMed2004

Quantitative examination of a perfusion microscope for the study of osmotic response of cells.

The perfusion microscope was developed for the study of the osmotic response of cells. In this microscope, the cells are immobilized in a transparent chamber mounted on the stage and exposed to a variety of milieus by perfusing the chamber with solutions of different concentrations. The concentration of the supplied solution is controlled using two variable-speed syringe pumps, which supply an isotonic solution and a hypertonic solution. Before using this system to characterize the osmotic response of cells, the change in the concentration of NaCl solution flowing through the chamber is examined quantitatively using a laser interferometer and an image processing technique. The NaCl concentration is increased from an isotonic condition to a hypertonic condition abruptly or gradually at a given constant rate, and decreased from a hypertonic condition to an isotonic condition. It is confirmed that the concentration is nearly uniform in the cross direction at the middle of the chamber, and the change in the NaCl concentration is reproducible. The average rate of increase or decrease in the measured concentration agrees fairly well with the given rate when the concentration is changed gradually at a constant rate. The rate of the abrupt change is also determined to be the highest limit achieved by the present method. As the first application of using the perfusion microscope for biological studies, the volume change of cells after exposure to a hypertonic solution is measured. Then, the hydraulic conductivity of the cell membrane is determinedfrom the comparison of the volume change between the experiment and the theoretical estimation for the measured change in the NaCl concentration of the perfused solution.

Adenocarcinoma↗
PubMed2003

Optoacoustic tomography using time-resolved interferometric detection of surface displacement.

We introduce a minimally invasive technique for optoacoustic imaging of turbid media using optical interferometric detection of surface displacement produced by thermoelastic stress transients. The technique exploits endogenous or exogenous optical contrast of heterogeneous tissues and the low attenuation of stress wave propagation to localize and image subsurface absorbers in optically turbid media. We present a system that utilizes a time-resolved high-resolution interferometer capable of angstrom-level displacement resolution and nanosecond temporal resolution to detect subsurface blood vessels within model tissue phantoms and a human forearm in vivo.

Absorption↗
PubMed2003

Optoacoustic determination of optical attenuation depth using interferometric detection.

We use a modified Mach-Zehnder interferometer to measure surface displacement resulting from the thermoelastic response of a target to the absorption of a short laser pulse with axial and temporal resolutions of 0.1 nm and 3 ns, respectively. These measurements are used in conjunction with a solution to the thermoelastic wave equation and a nonlinear optimization algorithm to extract optical attenuation depth. We demonstrate the ability to determine the effective optical attenuation depth of homogeneous targets with either diffuse or specular reflecting surfaces with a precision of <or=4% for attenuation depths spanning 0.1 to 2 mm.

Absorption↗
PubMed2003

Axial and peripheral eye length measured with optical low coherence reflectometry.

An optical low-coherence reflectometer (OLCR device) is described that allows the precise and noncontact measurement of eye length. The device measures eye length both on-axis and off-axis, thus enabling the determination of eye shape, an ocular parameter thought to be important in the development of refractive error. It is essential for several applications in ophthalmology and vision science. This improved OLCR device operates using a single-beam interferometer with a beam deflection mechanism that allows the precise measurement of eye length along the visual axis and within 15 deg horizontally and vertically from the fovea. The validity of this instrument and its revised software is evaluated by measuring the reproducibility of axial length results in an adult eye and an artificial eye, and by correlating axial eye length measured in a group of ten adult eyes with axial eye length obtained with A-scan ultrasound in the same eyes. The precision obtained with adult subjects is compared with that obtained with children.

Adult↗
PubMedDate not supplied

Photomechanical investigations on the stress-strain relationship in dentine macrostructure.

In this study photomechanical experiments were carried out to examine the relationship between macroscopic mechanical stress and strain gradients within the root dentine structure. Three-dimensional digital photoelasticity was used to study the stress distribution patterns in tooth models, while digital moire interferometry was used to study the strain gradients within the natural teeth. The stress analysis showed a distinct bending stress distribution, along faciolingual plane in the coronal and cervical regions of the tooth. There was a reduction in bending towards the apical third of the tooth model. The strain analysis displayed strain gradients in the axial (along the long axis of the tooth) and lateral (perpendicular to the long axis of the tooth) directions in dentine. There was a conspicuous reduction in strains from the cervical to the apical third of the root dentine. The root dentine displayed uniform distribution of normal strains. Although there was a steep increase in stresses from the inner core region to the outer surface of an isotropic tooth model, there were more uniform strain gradients in the natural dentine structure. It is apparent from these observations that complex organization of material properties facilitated distinct strain gradients in dentine structure during mechanical functions.

Anisotropy↗
PubMedDate not supplied

Optical probes and techniques for molecular contrast enhancement in coherence imaging.

Optics has played a key role in the rapidly developing field of molecular imaging. The spectroscopic nature and high-resolution imaging capabilities of light provide a means for probing biological morphology and function at the cellular and molecular levels. While the use of bioluminescent and fluorescent probes has become a mainstay in optical molecular imaging, a large number of other optical imaging modalities exist that can be included in this emerging field. In vivo imaging technologies such as optical coherence tomography and reflectance confocal microscopy have had limited use of molecular probes. In the last few years, novel nonfluorescent and nonbioluminescent molecular imaging probes have been developed that will initiate new directions in coherent optical molecular imaging. Classes of probes reviewed in this work include those that alter the local optical scattering or absorption properties of the tissue, those that modulate these local optical properties in a predictable manner, and those that are detected utilizing spectroscopic optical coherence tomography (OCT) principles. In addition to spectroscopic OCT, novel nonlinear interferometric imaging techniques have recently been developed to detect endogenous molecules. Probes and techniques designed for coherent molecular imaging are likely to improve the detection and diagnostic capabilities of OCT.

Animals↗
PubMedDate not supplied

Standing wave total internal reflection fluorescence microscopy to measure the size of nanostructures in living cells.

We present the first application of standing wave fluorescence microscopy (SWFM) to determine the size of biological nanostructures in living cells. The improved lateral resolution of less than 100 nm enables superior quantification of the size of subcellular structures. We demonstrate the ability of SWFM by measuring the diameter of biological nanotubes (membrane tethers formed between cells). The combination of SWFM with total internal reflection (TIR), referred to as SW-TIRFM, allows additional improvement of axial resolution by selective excitation of fluorescence in a layer of about 100 nm.

Equipment Design↗
PubMed2002

Optical measurement of human retinal macular pigment and its spatial distribution with age.

The existence of macular pigment (MP) in human eyes has been found to be of importance in the prevention of age-related macular degeneration (ARMD). A noninvasive technique of two-wavelength imaging fundus reflectometry was developed to measure the density distribution of this yellow pigment in retina in vivo. A total of 55 healthy human subjects were recruited and divided into three groups with average ages and sample sizes of 25.2+/-2.1 (N = 25), 40.2+/-8.3 (N = 13), and 67.5+/-7.1 years (N = 17), respectively. Only the MP distributions in the horizontal meridian of retinas are presented in this report. The results show that the average peak optical density of MP are 0.23+/-0.07, 0.21+/-0.05, and 0.25+/-0.06 from young to old groups, respectively. No significant difference is shown in the statistical t-test between the groups of the peak MP density. The half width of MP spatial distribution (HWMPD) are 4.8 degrees+/-1.5 degrees, 5.1 degrees+/-2.1 degrees and 7.7 degrees+/-2.0 degrees (1 degree = approximately 0.3 mm) from young to old groups, respectively. Mean HWMPD = approximately 5.6 degrees +/- 2.1 degrees. It shows that the area of MP is increased approximately by a rate of 0.06 degrees/yr according to the application of linear regression. However, the cause of the MP extension in the retina with age is unknown.

Adult↗
PubMed2001

Reconstitution of physiological microtubule dynamics using purified components.

Microtubules are dynamically unstable polymers that interconvert stochastically between polymerization and depolymerization. Compared with microtubules assembled from purified tubulin, microtubules in a physiological environment polymerize faster and transit more frequently between polymerization and depolymerization. These dynamic properties are essential for the functions of the microtubule cytoskeleton during diverse cellular processes. Here, we have reconstituted the essential features of physiological microtubule dynamics by mixing three purified components: tubulin; a microtubule-stabilizing protein, XMAP215; and a microtubule-destabilizing kinesin, XKCM1. This represents an essential first step in the reconstitution of complex microtubule dynamics-dependent processes, such as chromosome segregation, from purified components.

Animals↗
PubMed1967

Red cell slip at a wall in vitro.

Interferometric microscope observations of flowing blood indicate that the absolute number of red cells maintaining sliding contact with a wall is of the order 10(4) per square centi meter at low flow rates. Contacting cell oscillation and orientation results are given. The near wall local hematocrit is found to be relatively low.

Blood Viscosity↗
PubMed1969

Axonal outgrowth and cell migration in vitro from nervous system of cockroach embryos.

Brain and ganglia of embryonic Periplaneta americana were grown for 2 to 3 weeks in a chemically defined medium. Nerve fibers sprouted vigorously from intact brains and ganglia, interconnecting nerve cultures, and adjacent cultures of the digestive tract, Glia, tracheal, and nerve cells were present in large numbers in the migratory zone surrounding the explants.

Axons↗
PubMed1989

Activation of salivary secretion: coupling of cell volume and [Ca2+]i in single cells.

High-resolution differential interference contrast microscopy and digital imaging of the fluorescent calcium indicator dye fura-2 were performed simultaneously in single rat salivary gland acinar cells to examine the effects of muscarinic stimulation on cell volume and cytoplasmic calcium concentration ([Ca2+]i). Agonist stimulation of fluid secretion is initially associated with a rapid tenfold increase in [Ca2+]i as well as a substantial cell shrinkage. Subsequent changes of cell volume in the continued presence of agonist are tightly coupled to dynamic levels of [Ca2+]i, even during [Ca2+]i oscillations. Experiments with Ca2+ chelators and ionophores showed that physiological elevations of [Ca2+]i are necessary and sufficient to cause changes in cell volume. The relation between [Ca2+]i and cell volume suggests that the latter reflects the secretory state of the acinar cell. Agonist-induced changes in [Ca2+]i, by modulating specific ion permeabilities, result in solute movement into or out of the cell. The resultant cell volume changes may be important in modulating salivary secretion.

Animals↗
PubMed1997

Structure of DNA-cationic liposome complexes: DNA intercalation in multilamellar membranes in distinct interhelical packing regimes.

Cationic liposomes complexed with DNA (CL-DNA) are promising synthetically based nonviral carriers of DNA vectors for gene therapy. The solution structure of CL-DNA complexes was probed on length scales from subnanometer to micrometer by synchrotron x-ray diffraction and optical microscopy. The addition of either linear lambda-phage or plasmid DNA to CLs resulted in an unexpected topological transition from liposomes to optically birefringent liquid-crystalline condensed globules. X-ray diffraction of the globules revealed a novel multilamellar structure with alternating lipid bilayer and DNA monolayers. The lambda-DNA chains form a one-dimensional lattice with distinct interhelical packing regimes. Remarkably, in the isoelectric point regime, the lambda-DNA interaxial spacing expands between 24.5 and 57.1 angstroms upon lipid dilution and is indicative of a long-range electrostatic-induced repulsion that is possibly enhanced by chain undulations.

Bacteriophage lambda↗
PubMed1999

The immunological synapse: a molecular machine controlling T cell activation.

The specialized junction between a T lymphocyte and an antigen-presenting cell, the immunological synapse, consists of a central cluster of T cell receptors surrounded by a ring of adhesion molecules. Immunological synapse formation is now shown to be an active and dynamic mechanism that allows T cells to distinguish potential antigenic ligands. Initially, T cell receptor ligands were engaged in an outermost ring of the nascent synapse. Transport of these complexes into the central cluster was dependent on T cell receptor-ligand interaction kinetics. Finally, formation of a stable central cluster at the heart of the synapse was a determinative event for T cell proliferation.

Animals↗
PubMed1999

Focal adhesion motility revealed in stationary fibroblasts.

Focal adhesions (FAs) are clustered integrins and associated proteins that mediate cell adhesion and signaling. A green fluorescent protein-beta1 integrin chimera was used to label FAs in living cells. In stationary cells, FAs were highly motile, moving linearly for several plaque lengths toward the cell center. FA motility was independent of cell density and resulted from contraction of associated actin fibers. In migrating cells, FAs were stationary and only moved in the tail. FA motility in stationary cells suggests that cell movement may be regulated by a clutch-like mechanism by which the affinity of integrins to substrate may be altered in response to migratory cues.

3T3 Cells↗