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At least 703 records · Page 39Linked to original sources

PubMed2001

The catalytic efficiency of soybean lipoxygenase-1 is enhanced at low gravity.

Several cellular processes are modified when cells are placed under conditions of weightlessness. As yet, there is no coherent explanation for these observations, nor it is known which biomolecules might act as gravity sensors. Lipoxygenases generate leukotrienes and lipoxins from arachidonic acid, being responsible for many pharmacological and immunological effects, some of which are known to be affected by microgravity. In the course of the 28th parabolic flight campaign of the European Space Agency we measured the activity of pure soybean lipoxygenase-1 on linoleic acid, by a fibre optics spectrometer developed on purpose. It was found that microgravity reduced the apparent Michaelis-Menten constant (Km) of the enzymatic reaction to one fourth with respect to the 1 g control, whereas, the catalytic constant (k(cat)) was unaffected. Consequently, the catalytic efficiency of lipoxygenase-1 (k(cat)/Km) was approximately four-fold higher in flight than on ground. This unprecedented finding suggests that lipoxygenase-1 might be a molecular target for gravity.

Catalysis↗

PubMed1999

Short latency compound action potentials from mammalian gravity receptor organs.

Gravity receptor function was characterized in four mammalian species using far-field vestibular evoked potentials (VsEPs). VsEPs are compound action potentials of the vestibular nerve and central relays that are elicited by linear acceleration ramps applied to the cranium. Rats, mice, guinea pigs, and gerbils were studied. In all species, response onset occurred within 1.5 ms of the stimulus onset. Responses persisted during intense (116 dBSPL) wide-band (50 to 50,000 Hz) forward masking, whereas auditory responses to intense clicks (112 dBpeSPL) were eliminated under the same conditions. VsEPs remained after cochlear extirpation but were eliminated following bilateral labyrinthectomy. Responses included a series of positive and negative peaks that occurred within 8 ms of stimulus onset (range of means at +6 dBre: 1.0 g/ms: P1=908 to 1062 micros, N1=1342 to 1475 micros, P2=1632 to 1952 micros, N2=2038 to 2387 micros). Mean response amplitudes at +6 dBre: 1.0 g/ms ranged from 0.14 to 0.99 microV. VsEP input/output functions revealed latency slopes that varied across peaks and species ranging from -19 to -51 micros/dB. Amplitude-intensity slopes also varied ranging from 0.04 to 0.08 microV/dB for rats and mice. Latency values were comparable to those of birds although amplitudes were substantially smaller in mammals. VsEP threshold values were considerably higher in mammals compared to birds and ranged from -8.1 to -10.5 dBre 1.0 g/ms across species. These results support the hypothesis that mammalian gravity receptors are less sensitive to dynamic stimuli than are those of birds.

Acoustic Stimulation↗

PubMed1986

Pedoscope studies on neonatal activity and center of gravity after delivery.

Seventeen normal term infants delivered at the Jikei University School of Medicine were placed daily on a pedoscope in the supine and prone position after birth, and the movement of the gravity center and changes in the activities of the extremities were assessed. The results indicated that both the activity of the extremities and the movement of the gravity center were sluggish after birth, that both increased to reach peaks within 1 to 3 days, and that then temporary decreases occurred before they increased again. The probable reason for the temporary decrease in activity may be habituation or a decrement in the infant, and it is also presumed that the increase in activity after the transitory decrease reflects natural development.

Extremities↗

PubMed1993

A technique for prevention of sudden pressure loss on emptying of irrigation bags during arthroscopic surgery using gravity-fed irrigation systems.

Gravity-fed irrigation systems in arthroscopic surgery are safe and cheap, but visualization can be impaired by fluctuations in in-flow pressure, which leads to bleeding and temporary disruption of surgery. We describe a gravity-fed irrigation system using differential hydrostatic pressures in sequentially arranged irrigation bags that can be independently raised and lowered. This technique maintains a relatively steady flow and intra-articular pressure, thereby improving the quality of irrigation without having to resort to the more expensive pressure infusion systems, and minimizing the need for surgery under tourniquet.

Arthroplasty↗

PubMed1998

Intraoperative flexion against gravity as an indication of ultimate range of motion in individual cases after total knee arthroplasty.

To assess a method of predicting the final postoperative flexion in individual cases after total knee arthroplasty, 364 primary posterior cruciate-retaining total knee arthroplasties were reviewed retrospectively. The knees were subdivided into three preoperative flexion groups--I: poor motion (0 degrees to 85 degrees), II: intermediate motion (90 degrees to 110 degrees), and III: good motion (115 degrees to 140 degrees). There were 302 cases of osteoarthritis and 62 rheumatoid knees (12 juvenile rheumatoid). Correlation was made between preoperative; intraoperative, and postoperative (minimum 2-year follow-up) passive knee flexion for individuals. Intraoperative flexion against gravity was measured after capsular closure by passively flexing the patient's hip 90 degrees and allowing the weight of the lower leg to flex the knee joint. The overall mean value of postoperative flexion for all three groups was similar to preoperative and intraoperative flexion in both osteoarthritis and rheumatoid arthritis. In the poor motion group (I), postoperative flexion (103 degrees) was increased over preoperative flexion (84 degrees) but similar to intraoperative flexion (104 degrees). In the intermediate group (II), postoperative flexion (110 degrees) was similar to both the preoperative flexion (108 degrees) and intraoperative flexion (110 degrees). In the good group (III), postoperative flexion (119 degrees) tended to be less than preoperative flexion (123 degrees) and more than intraoperative flexion (116 degrees), but the differences were not statistically significant. When comparing preoperative and intraoperative flexion to postoperative flexion for individual cases, 55% of knees had postoperative flexion +/-10 degrees of their preoperative value, while 97% of knees had postoperative flexion +/-10 degrees of their intraoperative value. This study indicates that the final postoperative mean flexion for a group of patients with poor preoperative flexion (<85 degrees) and for individual cases (regardless of their preoperative mobility) can best be predicted by intraoperative flexion against gravity rather than by a preoperative value.

Arthritis, Juvenile↗

PubMed2003

Increased levels of UV-induced protease activity in human UVAP-1 cells exposed to gravity-changing stress: involvement of E-64-sensitive proteases in suppression of UV mutagenicity.

Under the 1G condition, the increase in antipain-sensitive protease activity promptly after UV (mainly 254 nm wavelength) irradiation in cultured human cells is detected and found to be one of the intriguing events involved in suppression of cell mutability. It was found that two cell lines, RSa and its variant UVAP-1 cells are applicable; the former is hypermutable and not susceptible to protease activation, while the latter is hypomutable and susceptible. In the present study it was investigated whether the increase in protease activity by UV irradiation is also observed in hypomutable human UVAP-1 cells exposed to gravity-changing stress and whether the increase is involved in suppression of UV mutagenicity. Exposure of human UVAP-1 cells to gravity-changing stress such as free-fall and parabolic flight prior to UV irradiation resulted in a pronounced increase in protease activity, but not to hypergravity conditions (2 and 10G) prior to UV irradiation. To characterize the proteases, components of lysates from the cells exposed to free-fall prior to UV irradiation were fractionated by high performance liquid chromatography, indicating two separate fractions with highly increased levels of E-64-sensitive protease activity. In the cells treated with E-64 during their exposure to free-fall, K-ras codon 12 base substitution mutation was detected after UV irradiation, although the mutation was not detected after UV irradiation alone. Thus, the increase in E-64-sensitive protease activity may be involved in the suppression of UV mutagenicity in UVAP-1 cells exposed to free-fall.

Antipain↗

PubMed2003

Influence of gravity on radiographic contrast material-based measurements of regional blood flow distribution.

RATIONALE AND OBJECTIVES: Radiographic measurement of regional blood flow distribution in the lungs is potentially biased because the contrast material used to track flow is denser than blood. The authors performed this study to evaluate the effect of gravity on flow estimates by using an experimental test phantom and numeric simulations. MATERIALS AND METHODS: Cross-sectionally uniform boluses of radiopaque contrast material were delivered at the upstream end of a horizontal inlet tube connected to a downstream axisymmetric bifuration attached to collecting tubing spirals. The phantom was imaged by using both planar angiography and dynamic multi-detector row computed tomography (CT) during the passage of the bolus through the phantom. The images were analyzed to determine the relative amounts of contrast material traveling through the top and bottom branches of the bifurcation by using varying Reynolds numbers and ratios of inlet tube volume to bolus volume. Numeric simulations of flow within a straight channeL with use of a dispersion operator intended to simulate settling of the bolus due to gravity, were performed under conditions representative of those in the experiments. RESULTS: When the plane of the bifurcation was vertical and actual flow through the two branches was equal, the fraction of contrast material passing through the downward-directed branch increased with decreasing Reynolds number and increasing inlet tube-bolus volume ratio. This occurred in both the experiments and the simulations. CONCLUSION: Because in the circulation Reynolds number decreases and pathway length increases with decreasing vessel diameter, the accuracy of regional flow measurements obtained with angiography or CT within the lungs may be limited by density differences between contrast material and blood.

Angiography↗

PubMed1997

Vestibular function and sensory interaction in altered gravity.

The effects of weightlessness on vestibular function have been studied since the beginning of manned spaceflight. The results of these studies have been highly variable and to some extent even contradictory, which makes it difficult to draw unambiguous conclusions. This variability is probably due to at least three factors: (1) individual differences in the adaptive process, (2) non-standardized experimental methods and conditions, (3) a lack of integrated experiments. For this reason, we have used a single integrated approach with a specially developed battery of tests. The results thus obtained for 21 cosmonauts on short- and long-term flights are reviewed here, and discussed in the light of the results obtained by others. Changes in the operation of the vestibular system and in all functions based on vestibular afferent input are commonly observed in spaceflight. These changes are characteristic for the process of adaptation and re-adaptation to altered gravity. They occur in a high proportion of persons exposed to such conditions, although there are individual differences with regard to severity, nature, time and duration of occurrence, and the dynamics of the process. Analysis of the observations in a large number of cosmonauts has permitted to distinguish three types of adaptation of the system to altered gravity. The first type of adaptation is characterized by a strong response to any stimulus during the initial adaptation period. The second type of adaptation is characterized by responses that are drastically decreased or even absent. The third type of adaptation is distinguished by the selective response of the sensory system to certain types of stimulation only. After long-term missions the process of re-adaptation usually takes a more severe course than the earlier process of adaptation to microgravity. Both adaptation and re-adaptation follow an undulating course, in which adaptation and re-adaptation are alternating. This is most conspicuous during long-term flights, and it suggests that in the initial stage of adaptation to weightlessness the vestibular input plays a dominant role, while at the end of the adaptation process the visual input prevails.

Eye Movements↗

PubMed1994

Effects of gravity on the cellular response to epidermal growth factor.

EGF and related polypeptides are involved in the regulation of cell growth and differentiation of continuously regenerating tissues, in tissue repair processes and in placental and fetal development. Their initial mode of action generally constitutes binding to specific plasma membrane localized receptors, transduction of the signal across the plasma membrane, subsequent activation of signalling pathways in the cell, and the induction of early nuclear gene expression. EGF-induced signal transmission from the plasma membrane to the nucleus has been studied in microgravity in order to gain insight in the molecular mechanisms that constitute the effects of gravity on cell growth. Exposure of human A431 cells to microgravity strongly suppresses EGF- and PMA-induced c-fos and c-jun expression. In contrast, forskolin- and A23187-induced c-fos expression and constitutive beta-2 microglobulin expression remain unaffected. This suggests that microgravity differentially modulates EGF-induced signal transduction pathways. Since both EGF and PMA are known to be activators of PKC, which is not the case for forskolin and A23187, PKC-mediated signal transduction may be a cellular target for microgravity. Inhibition of EGF-induced c-fos expression by microgravity occurs downstream of the initiation of EGF-induced signal transduction, i.e., EGF binding and EGFR redistribution. In addition to PKC signaling, actin microfilament organization appears to be sensitive to microgravity. Therefore, the inhibition of signal transduction by microgravity may be related to alterations in actin microfilament organization. The fact that early gene expression is affected by agents that alter the organization of the actin microfilament system supports this hypothesis. The decrease in c-fos and c-jun expression in microgravity may result in the decreased formation of the FOS and JUN proteins. Consequently, a short-term reduction in gene expression in microgravity may have a more dramatic effect over the long term, since both the JUN and FOS protein families are required for normal cell cycle progression. However, since more than 20 years of manned spaceflight have shown that humans can survive in microgravity for prolonged periods, it appears that cells in the human body can partly or completely overcome gravitational stress. Although some insight in the molecular basis on human cells has been obtained, future studies will be needed for a better understanding of the grounds for alterations in the cellular biochemistry due to altered gravity conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Actin Cytoskeleton↗

PubMed2002

Vector-averaged gravity regulates gene expression of receptor activator of NF-kappaB (RANK) ligand and osteoprotegerin in bone marrow stromal cells via cyclic AMP/protein kinase A pathway.

Bone loss due to unloading of the skeleton may be caused by an acceleration of osteoclastic bone resorption as well as a decline of osteoblastic bone formation. Recently, two molecular species that play important roles in osteoclastogenesis were discovered: (i) the receptor activator of NF-kappaB ligand (RANKL)/osteoprotegerin (OPG) ligand/osteoclast differentiation factor induces osteoclastogenesis; and (ii) the OPG/osteoclastogenesis inhibitory factor potently inhibits osteoclastogenesis. To investigate the effects of gravity on gene expression of RANKL and OPG, a mouse bone marrow-derived stromal cell line, ST2, was cultured on a single axis clinostat, which generates a vector-averaged gravity environment. Northern blot analysis revealed that RANKL mRNA was increased, whereas that of OPG decreased. The clinostat culture also caused an increase in intracellular cyclic (cAMP) level. Both forskolin and dibutyryl-cAMP mimicked the regulation of RANKL and OPG transcription in clinostat culture. These modulations of gene expression in clinostat culture were blocked by a protein kinase A (PKA) inhibitor, H89, but not by a cyclooxygenase inhibitor, indomethacin. The enhancement of RANKL gene expression under clinostat culture and its inhibition by H89 were confirmed by a reporter assay with the murine RANKL 5'-flanking region. These results suggest that modulations of RANKL and OPG expression in stromal cells might be one of the causes of bone loss during skeletal unloading. An elevation of intracellular cAMP level caused through an as yet undetermined pathway is involved in modulation of RANKL and OPG expression during clinostat culture.

Animals↗

PubMed2005

High-throughput nanoliter sample introduction microfluidic chip-based flow injection analysis system with gravity-driven flows.

In this work, a simple, robust, and automated microfluidic chip-based FIA system with gravity-driven flows and liquid-core waveguide (LCW) spectrometric detection was developed. The high-throughput sample introduction system was composed of a capillary sampling probe and an array of horizontally positioned microsample vials with a slot fabricated on the bottom of each vial. FI sample loading and injection were performed by linearly moving the array of vials filled alternately with 50-microL samples and carrier, allowing the probe inlet to enter the solutions in the vials through the slots sequentially and the sample and carrier solution to be introduced into the chip driven by gravity. The performance of the system was demonstrated using the complexation of o-phenanthroline with Fe(II) as a model reaction. A 20-mm-long Teflon AF 2400 capillary (50-microm i.d., 375-microm o.d.) was connected to the chip to function as a LCW detection flow cell with a cell volume of 40 nL and effective path length of 1.7 cm. Linear absorbance response was obtained in the range of 1.0-100 microM Fe(II) (r2=0.9967), and a good reproducibility of 0.6% RSD (n=18) was achieved. The sensitivity was comparable with that obtained using conventional FIA systems, which typically consume 10,000-fold more sample. The highest sampling throughput of 1000 h-1 was obtained by using injection times of 0.08 and 3.4 s for sample and carrier solution, respectively, with a sample consumption of only 0.6 nL for each cycle.

Journal Article↗

PubMed1999

The behavioral responses by larvae of the water mite Unionicola foili (Acari: Unionicolidae) to gravity, light and host chemicals: adaptations for transmission success?

The life cycle of the water mite Unionicola foili includes larvae that parasitize chironomid dipterans, and nymphs and adults that occur in association with the freshwater mussel Utterbackia imbecillis. The georesponses and photoresponses of larval U. foili in the presence of chemical substances from chironomids and mussels both prior to (= pre-chironomid larvae) and after their parasitism with chironomids (= post-chironomid larvae) were examined in the laboratory. The responses of larval U. foili to light and gravity changed during larval ontogeny and varied depending on the chemistry of the medium in which they were examined. Pre-chironomid larvae preferentially responded to water modified by chironomids given that negative phototaxis and positive georesponses were elicited only in the presence of water that had been modified by these hosts. Post-chironomid larvae exhibited host-induced negative phototaxis only in the presence of mussel-modified water. Post-chironomid larvae were consistently geopositive when exposed to water modified by mussels or chironomids. The pattern of responses exhibited by larval U. foili to light and gravity are interpreted as adaptations for locating potential hosts in the field.

Acari↗

PubMed2001

The development of gravity models for hospital patient flows under system change: a Bayesian modelling approach.

This paper discusses models for the impact on patient referral flows from homes to hospitals of reconfigurations of emergency hospital services. Such system change might involve new hospital sites, or expanded bed numbers at some sites, together with possible closure of emergency units at other hospitals. In terms of a gravity model for the flows of patients, this corresponds to removing a destination or adding a new one. While retaining a gravity type approach to this problem, the relevance of supply weighting by distance within the broader accessibility concept is stressed since the independence from irrelevant alternatives property is generally inapplicable. This accessibility based approach may be implemented as a general linear model, with a Poisson outcome, and a Bayesian estimation and predictive approach is adopted. In the context of patient hospitalisations, this facilitates prediction of new patient flows following hospital reconfiguration. A UK based case study of small residential areas and hospitals in North East London and Essex is presented within the context of a review of emergency hospital siting in London.

Bayes Theorem↗

PubMed2003

Improvement of the ethanol productivity in a high gravity brewing at pilot plant scale.

A 23 full factorial design was used to study the influence of different experimental variables, namely wort gravity, fermentation temperature and nutrient supplementation, on ethanol productivity from high gravity wort fermentation by Saccharomyces cerevisiae (lager strain), under pilot plant conditions. The highest ethanol productivity (0.69 g l(-1) h(-1)) was obtained at 20 degrees P [degrees P is the weight of extract (sugar) equivalent to the weight of sucrose in a 100 g solution at 20 degrees C], 15 degrees C, with the addition of 0.8% (w/v) yeast extract, 24 mg l(-1) ergosterol and 0.24% (v/v) Tween 80.

Biomass↗

PubMed1992

Infants' sensitivity to effects of gravity on visible object motion.

A preference method probed infants' perception of object motion on an inclined plane. Infants viewed videotaped events in which a ball rolled downward (or upward) while speeding up (or slowing down). Then infants were tested with events in which the ball moved in the opposite direction with appropriate or inappropriate acceleration. Infants aged 7 months, but not 5 months, looked longer at the test event with inappropriate acceleration, suggesting emerging sensitivity to gravity. A further study tested whether infants appreciate that a stationary object released on an incline moves downward rather than upward; findings again were positive at 7 months and negative at 5 months. A final study provided evidence, nevertheless, that 5-month-old infants discriminate downward from upward motion and relate downward motion in videotaped events to downward motion in live events. Sensitivity to certain effects of gravity appears to develop in infancy.

Acceleration↗

PubMed2001

A phenomenological description of space-time noise in quantum gravity.

Space-time 'foam' is a geometric picture of the smallest size scales in the Universe, which is characterized mainly by the presence of quantum uncertainties in the measurement of distances. All quantum-gravity theories should predict some kind of foam, but the description of the properties of this foam varies according to the theory, thereby providing a possible means of distinguishing between such theories. I previously showed that foam-induced distance fluctuations would introduce a new source of noise to the measurements of gravity-wave interferometers, but the theories are insufficiently developed to permit detailed predictions that would be of use to experimentalists. Here I propose a phenomenological approach that directly describes space-time foam, and which leads naturally to a picture of distance fluctuations that is independent of the details of the interferometer. The only unknown in the model is the length scale that sets the overall magnitude of the effect, but recent data already rule out the possibility that this length scale could be identified with the 'string length' (10-34 m < Ls < 10-33 m). Length scales even smaller than the 'Planck length' (LP approximately 10-35 m) will soon be probed experimentally.

Journal Article↗

PubMed2003

A strong astrophysical constraint on the violation of special relativity by quantum gravity.

Special relativity asserts that physical phenomena appear the same to all unaccelerated observers. This is called Lorentz symmetry and relates long wavelengths to short ones: if the symmetry is exact it implies that space-time must look the same at all length scales. Several approaches to quantum gravity, however, suggest that there may be a microscopic structure of space-time that leads to a violation of Lorentz symmetry. This might arise because of the discreteness or non-commutivity of space-time, or through the action of extra dimensions. Here we determine a very strong constraint on a type of Lorentz violation that produces a maximum electron speed less than the speed of light. We use the observation of 100-MeV synchrotron radiation from the Crab nebula to improve the previous limit by a factor of 40 million, ruling out this type of Lorentz violation, and thereby providing an important constraint on theories of quantum gravity.

Journal Article↗

PubMed2004

Muscle hypertrophy following 5-week resistance training using a non-gravity-dependent exercise system.

AIM: The efficacy of a mechanical, gravity-independent resistance exercise (RE) system to induce strength gains and muscle hypertrophy was validated. Designed for space crew in orbit, this technique offers resistance during coupled concentric and eccentric actions by utilizing the inertia of a rotating flywheel(s), set in motion by the trainee. METHODS: Ten middle-aged (30-53 years) men and women performed four sets of seven maximal, unilateral (left limb) knee extensions two or three times weekly for 5 weeks. Knee extensor force and electromyographic (EMG) activity of the three superficial quadriceps muscles were measured before and after this intervention. In addition, with the use of magnetic resonance imaging (MRI), volume of individual knee extensor and ankle plantar flexor muscles was assessed. RESULTS: Over the 12 training sessions, the average concentric (CON) and eccentric (ECC) force generated during exercise increased by 11% (P < 0.05). Likewise, maximal isometric strength (maximal voluntary contraction, MVC) at 90 and 120 degrees knee angle increased by (P < 0.05) 11 and 12% respectively, after training. Neither individual quadriceps muscle showed a change (P > 0.05) in maximal integrated EMG (iEMG) activity. Quadriceps muscle volume increased by 6.1% (P < 0.05). Although the magnitude of response varied, all individual quadriceps muscles showed increased (P < 0.05) volume after training. As expected, ankle plantar flexor volume of the trained limb was unchanged (P > 0.05). Likewise, MVC, CON and ECC force, iEMG and knee extensor and plantar flexor muscle volume were unaltered (P > 0.05) in the right, non-trained limb. CONCLUSION: The results of this study show that the present RE regimen produces marked muscle hypertrophy and important increases in maximal voluntary strength and appears equally effective as RE paradigms using gravity-dependent weights, in this regard.

Adult↗