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At least 541 records · Page 30Linked to original sources
PubMed1987

Gravitational and magnetic activation methods applied to cultured cells (LK 35.2).

Monoclonal antibody 10.2-16 is directed toward the mouse class II major histocompatibility complex gene product 1-Ak expressed on the cell line LK35.2. Instead of activating cells by fluorophor we used (acrylamide-coated) heavy and magnetic microspheres of 0.6 micron in radius. These microspheres are chemically coupled (carbodiimide method) with the antibody toward the surface antigen. The cells are observed through a microscope with horizontal alignment, as they sediment in a (temperature controlled) tube with square cross-section. Stokes Law allows the determination of the density of cells (first alone) using viscosity and density of Dulbecco's modified Eagle's Medium together with the observed mean sedimentation velocity (66 microns/min) and a mean diameter of 10 microns. We found a density of 1.0558 +/- 0.0028 g/cm3 at 10 degrees C. Independently, thinly coated, heavy (and magnetizable) microspheres with the cited antibody are attached to cells and observed likewise. The increased sedimentation velocity permits us to show that the cells were fully covered with microspheres (290 per cell). A magnetic field gradient opposing gravity moved these cells against gravity with two different mean velocities, 340 microns/min and 850 microns/min. The higher velocity resulted in 290 particles per cell, the lower one in 130 particles per cell. The limits for the expansion of this method to smaller particle sizes (down to 10 nm) are evaluated.

Antibodies, Monoclonal↗
PubMed1983

Gravitational effects on human cardiovascular responses to isometric muscle contractions.

Isometric exercise induces profound cardiovascular adaptations increasing mean arterial pressure and heart rate. We investigated effects of simulated +Gz and -Gz respectively on the central and peripheral cardiovascular system. Sustained handgrip exercise was performed at 40% of maximum for 2 minutes in five subjects. This maneuver increased mean arterial pressure by 40-45 mm Hg both during head out water immersion which simulates weightlessness, as well as bedrest during -25, 0, and +25 degrees tilt from the horizontal. Lower body negative pressure (-60 mm Hg for 10 min) attenuated the response to handgrip exercise to 30 mm Hg. It also increased the heart rate minimally by about 20 beats per minute while the water immersion, as well as head up, head down and horizontal bedrest showed increments of about 50 beats per min. It was concluded that the response to isometric contraction is mediated through the high pressure baroreceptors, because similar responses were seen during stresses producing a wide variation in central venous pressure. During lower body negative pressure the increased sympathetic nervous activity itself increased resting heart rate and mean arterial pressure. The responses to static exercise were, therefore, weaker.

Adaptation, Physiological↗
PubMed1983

Gravitational effects on plant growth hormone concentration.

Numerous studies, particularly those of H. Dolk in the 1930's, established by means of bio-assay, that more growth hormone diffused from the lower, than from the upper side of a gravity-stimulated plant shoot. Now, using an isotope dilution assay, with 4,5,6,7 tetradeutero indole-3-acetic acid as internal standard, and selected ion monitoring-gas chromatography-mass spectrometry as the method of determination, we have confirmed Dolk's finding and established that the asymmetrically distributed hormone is, in fact, indole-3-acetic acid (IAA). This is the first physico-chemical demonstration that there is more free IAA on the lower sides of a geo-stimulated plant shoot. We have also shown that free IAA occurs primarily in the conductive vascular tissues of the shoot, whereas IAA esters predominate in the growing cortical cells. Now, using an especially sensitive gas chromatographic isotope dilution assay we have found that the hormone asymmetry also occurs in the non-vascular tissue. Currently, efforts are directed to developing isotope dilution assays, with picogram sensitivity, to determine how this asymmetry of IAA distribution is attained so as to better understand how the plant perceives the geo-stimulus.

Avena↗
PubMed1992

Understanding the organization of the amphibian egg cytoplasm: gravitational force as a probe.

A combination of hypergravity (centrifugation) and hypogravity (clinostat) studies have been carried out on amphibian (frog, Xenopus) eggs. The results reveal that the twinning caused by centrifugation exhibits substantial spawning to spawning variation. That variation can be attributed to the apparent viscosity of the egg's internal cytoplasm. Simulated hypogravity results in a relocation of the egg's third (horizontal) cleavage furrow, towards the equator. Substantial egg-to-egg variation is also observed in this "cleavage effect". For interpreting spaceflight data and for using G-forces as probes for understanding the egg's architecture the egg variation documented herein should be considered.

Animals↗
PubMed1994

Gravitational response of the slime mold Physarum.

The acellular slime mold Physarum polycephalum is used as a model system to investigate the graviresponse of single cells which possess no receptors specialized for the perception of gravity. To obtain insights into the gravity-signal transduction mechanism the light response of the cell is used: Macroplasmodia of the slime mold show clear geo- and phototaxes. Gravity increases and white light decreases transiently the contraction frequency of plasmodial strands whereby both responses follow the same time pattern. Since mitochondria play a major role in changing the contraction rhythm in response to light and gravity stimuli, the simultaneous and subsequent inductions of the opposing light and gravity responses and their mutual influences on one another were investigated. The experiments were performed in weightlessness (0 g)--simulated on the fast-rotating clinostat as well as in actual weightlessness during the IML-1 Space Shuttle mission. The results indicate that mitochondria (chondriome) are part of the acceleration-stimulus reaction chain in Physarum. Two models for a direct gravireceptor mechanism are discussed.

Animals↗
PubMed2006

Different elution modes and field programming in gravitational field-flow fractionation: field programming using density and viscosity gradients.

In previous papers, several approaches to programming of the resulting force field in GFFF were described and investigated. The experiments were dealing with flow-velocity and channel thickness, i.e. factors influencing hydrodynamic lift forces (HLF). The potential of density and viscosity of carrier liquid for field programming was predicted and demonstrated by preliminary experiments. This work is devoted to experimental verification of the influence of carrier liquid density and viscosity. Several carrier liquid density and simultaneously viscosity gradients using water-methanol mixtures are in this work implemented in the separation of a model silica mixture. Working with the water-methanol gradients, one is not able to separate the influence of density from the contribution of viscosity. However, we found experimental conditions to show the isolated effect of carrier liquid density (two water-methanol mixtures of equal viscosity differing in their densities). In order to demonstrate the isolated effect of viscosity, we implemented in this work a new system of (hydroxypropyl)methyl cellulose (HPMC) carrier liquids. Three different HPMC compositions enabled to vary the viscosity more than two times at almost constant density. With increasing carrier liquid viscosity, the focusing and elevating trend was clearly pronounced for 5 and 10 microm silica particles. By the isolated effect of increased viscosity, the centre of the 10 microm particle zone was elevated to the streamline at 16% of the channel height. These experiments have shown that the influence of carrier liquid viscosity on HLF should be taken into account even at higher levels above the channel bottom, i.e. beyond the near-wall region. Further, it is shown that higher value of carrier liquid viscosity improves the separation of the model mixture in terms of time and resolution.

Fractionation, Field Flow↗
PubMed2005

Cerebral oxygenation declines despite maintained orthostatic tolerance after brief exposure to gravitational stress.

We examined the effect of a single 120 s of exposure to +3Gz (head-to-foot inertial forces) centrifugation as orthostatic stress on cerebral oxygenation (oxy-Hb) and cerebral blood volume (CBV) changes in response to stand test, in order to relate the occurrence of altered cerebral oxygenation control to any increase in sympathetic activity. Frontal near-infrared spectroscopy and mean arterial blood pressure at brain level (MAPbrain) were recorded in 14 subjects in supine and then in standing (10 min) position, before and after +3Gz centrifugation. The decrease in oxy-Hb (-7 +/- 5 a.u. versus -27 +/- 4 a.u., P<0.001) and in CBV (-6 +/- 10 a.u. versus -15 +/- 8 a.u., P<0.05) upon standing was more important after +3Gz centrifugation, with unchanged MAPbrain (-8 +/- 8 mmHg versus -3 +/- 11 mmHg). Upon standing, the high-frequency component of heart rate was lower (1090 +/- 460 ms2 versus 827 +/- 412 ms2, P<0.05) after +3Gz centrifugation. These findings suggest a downward shift in the static cerebral autoregulatory curve. We conclude that cerebral vasoconstriction might have occurred without centrally mediated increase in the entire peripheral sympathetic activity of the body.

Adult↗
PubMed1999

High-resolution, submicron particle size distribution analysis using gravitational-sweep sedimentation.

Sedimentation velocity is a powerful tool for the analysis of complex solutions of macromolecules. However, sample turbidity imposes an upper limit to the size of molecular complexes currently amenable to such analysis. Furthermore, the breadth of the particle size distribution, combined with possible variations in the density of different particles, makes it difficult to analyze extremely complex mixtures. These same problems are faced in the polymer industry, where dispersions of latices, pigments, lacquers, and emulsions must be characterized. There is a rich history of methods developed for the polymer industry finding use in the biochemical sciences. Two such methods are presented. These use analytical ultracentrifugation to determine the density and size distributions for submicron-sized particles. Both methods rely on Stokes' equations to estimate particle size and density, whereas turbidity, corrected using Mie's theory, provides the concentration measurement. The first method uses the sedimentation time in dispersion media of different densities to evaluate the particle density and size distribution. This method works provided the sample is chemically homogeneous. The second method splices together data gathered at different sample concentrations, thus permitting the high-resolution determination of the size distribution of particle diameters ranging from 10 to 3000 nm. By increasing the rotor speed exponentially from 0 to 40,000 rpm over a 1-h period, size distributions may be measured for extremely broadly distributed dispersions. Presented here is a short history of particle size distribution analysis using the ultracentrifuge, along with a description of the newest experimental methods. Several applications of the methods are provided that demonstrate the breadth of its utility, including extensions to samples containing nonspherical and chromophoric particles.

Deuterium Oxide↗
PubMed2001

Assessment of inertial and gravitational inputs to the vestibular system.

A new device for the assessment of instantaneous angular and linear accelerations of the head is presented, which is based on four linear tri-axial accelerometers suitably attached to the head by an helmet. A procedure for reproducible helmet placement and calibration is given. A method is also illustrated to work out the different linear accelerations sensed by the vestibular organs in the left and right labyrinths and the components of the angular acceleration sensed by their semicircular canals. The computation is based on few individual parameters describing the helmet position with respect to external landmarks and on the average internal position and orientation of the vestibula. The purpose is to study the components of internal inertial forces, which represent the primary inputs to the vestibular system devoted to equilibrium and oculomotor control. The system is designed to be of easy application during rehabilitation exercises and in clinical environment during diagnostic and therapeutic manoeuvres. The prototype is tested with simple free movements such as "yes", "no", and gait.

Acceleration↗
PubMed2001

Size- and shape-dependent separation of TiO2 colloidal sub-populations with gravitational field flow fractionation.

The simplest field flow fractionation technique, which uses the earth's gravity as the external field is applied to isolate two populations, which differ in both shape and size, from a polydisperse sub-micron TiO2 powder of homogenous density. The fraction eluted first is spherical with an average diameter of 0.31 microm while the second fraction is ellipsoidal and can be associated with a 0.45 microm hydrodynamic diameter. Elution conditions appeared to be very sensitive to electrolyte and surfactant characteristics in the carrier phase as well as on the sample concentration. Using 25 microl (1%, w/w) sample suspension, separations of spherical from ovoid particles was performed in almost 2 h with a mobile phase of 0.001 M KNO3-0.01% (v/v) Fl-70 in water in a 0.025-cm thick channel made of polystyrene walls.

Chemical Fractionation↗
PubMed2003

Sonication effect on cellular material in sedimentation and gravitational field flow fractionation.

Sonication procedures are generally used prior to field flow fractionation (FFF) separation in order to produce suspensions without aggregates. Yeast cells manufactured in active dry wine yeast (ADWY) were placed in an ultrasound water bath in order to disrupt possible clumps and to obtain a single-cell suspension to be used in optimal conditions during fermentation processes. In order to determine whether this sample preparation procedure meets absolute needs, different yeast samples before and after sonication were analysed by two field flow fractionation techniques. It is shown that 2 min of sonication in the sample preparation process is sufficient to obtain an optimal dispersion of the yeast cells, that is, without critical percentage of aggregates. To demonstrate this effect, photographs of the yeast cell suspensions were performed with non-sonicated and sonicated yeast sample dispersion. The resulting data are compared with the elution profiles obtained from the two different FFF techniques. It is demonstrated that fractogram profiles prove the effectiveness of sonication methodologies.

Fractionation, Field Flow↗