SEARCH · PubMed Health

Results for “GRAVITY”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57Linked to original sources

PubMed1997

Evidence for the involvement of carbonic anhydrase and urease in calcium carbonate formation in the gravity-sensing organ of Aplysia californica.

To better understand the mechanisms that could modulate the formation of otoconia, calcium carbonate granules in the inner ear of vertebrate species, we examined statoconia formation in the gravity-sensing organ, the statocyst, of the gastropod mollusk Aplysia californica using an in vitro organ culture model. We determined the type of calcium carbonate present in the statoconia and investigated the role of carbonic anhydrase (CA) and urease in regulating statocyst pH as well as the role of protein synthesis and urease in statoconia production and homeostasis in vitro. The type of mineral present in statoconia was found to be aragonitic calcium carbonate. When the CA inhibitor, acetazolamide (AZ), was added to cultures of statocysts, the pH initially (30 min) increased and then decreased. The urease inhibitor, acetohydroxamic acid (AHA), decreased statocyst pH. Simultaneous addition of AZ and AHA caused a decrease in pH. Inhibition of urease activity also reduced total statoconia number, but had no effect on statoconia volume. Inhibition of protein synthesis reduced statoconia production and increased statoconia volume. In a previous study, inhibition of CA was shown to decrease statoconia production. Taken together, these data show that urease and CA play a role in regulating statocyst pH and the formation and maintenance of statoconia. CA produces carbonate ion for calcium carbonate formation and urease neutralizes the acid formed due to CA action, by production of ammonia.

Animals↗

PubMed2005

Characterization of very high gravity ethanol fermentation of corn mash. Effect of glucoamylase dosage, pre-saccharification and yeast strain.

Ethanol was produced from very high gravity mashes of dry milled corn (35% w/w total dry matter) under simultaneous saccharification and fermentation conditions. The effects of glucoamylase dosage, pre-saccharification and Saccharomyces cerevisiae strain on the growth characteristics such as the ethanol yield and volumetric and specific productivity were determined. It was shown that higher glucoamylase doses and/or pre-saccharification accelerated the simultaneous saccharification and fermentation process and increased the final ethanol concentration from 106 to 126 g/kg although the maximal specific growth rate was decreased. Ethanol production was not only growth related, as more than half of the total saccharides were consumed and more than half of the ethanol was produced during the stationary phase. Furthermore, a high stress tolerance of the applied yeast strain was found to be crucial for the outcome of the fermentation process, both with regard to residual saccharides and final ethanol concentration. The increased formation of cell mass when a well-suited strain was applied increased the final ethanol concentration, since a more complete fermentation was achieved.

Cell Culture Techniques↗

PubMed1999

Autolysis of Escherichia coli and Bacillus subtilis cells in low gravity.

The role of gravity in the autolysis of Bacillus subtilis and Escherichia coli was studied by growing cells on Earth and in microgravity on Space Station Mir. Autolysis analysis was completed by examining the death phase or exponential decay of cells for approximately 4 months following the stationary phase. Consistent with published findings, the stationary-phase cell population was 170% and 90% higher in flight B. subtilis and E. coli cultures, respectively, than in ground cultures. Although both flight autolysis curves began at higher cell densities than control curves, the rate of autolysis in flight cultures was identical to that of their respective ground control rates.

Bacillus subtilis↗

PubMed2001

The importance of valve alignment in determining the pressure/flow characteristics of differential pressure shunt valves with anti-gravity devices.

OBJECT: The proper functioning of shunt valves in vivo is dependent on many factors, including the valve itself, the anti-siphon device or ASD (if included), patency of inlet and outlet tubing, and location of the valve. One important, but sometimes overlooked, consideration in valve function is the valve location relative to the tip of the ventricular inlet catheter. As with any pressure measurement, the zero or reference position is an important concept. In the case of shunt valves, the position of the proximal inlet catheter tip is fixed and therefore serves as the reference point for all pressure measurements. This study was conducted to document the importance of this relationship for the pressure/flow characteristics of the shunt valve. METHODS: We bench-tested differential pressure valves (with integral anti-gravity devices; AGDs) from three manufacturers. Valves were connected to an "infinite" reservoir, and the starting head pressure for each was determined from product inserts. The inlet catheter tip was fixed at this position, and the valve body was moved in relation to the inlet catheter tip. Outflow rates were determined gravimetrically for positions varying between 4 cm above and 8 cm below the inlet catheter tip. CONCLUSIONS: All differential pressure valves utilized in this study that contained AGDs showed significant increases in outflow rate as the valve body was moved incrementally below the level of the inlet catheter tip. To allow functioning as a zero-hydrostatic pressure differential pressure valve, the AGD and the inlet catheter tip should be aligned at the same horizontal level.

Cerebrospinal Fluid Pressure↗

PubMed2006

Does reduced gravity alter cellular response to ionizing radiation?

This review addresses the purported interplay between actual or simulated weightlessness and cellular response to ionizing radiation. Although weightlessness is known to alter several cellular functions and to affect signaling pathways implicated in cell proliferation, differentiation and death, its influence on cellular radiosensitivity has so far proven elusive. Renewed controversy as to whether reduced gravity enhances long-term radiation risk is fueled by recently published data that claim either overall enhancement of genomic damage or no increase of radiation-induced clastogenicity by modeled microgravity in irradiated human cells. In elucidating this crucial aspect of space radiation protection, ground-based experiments, such as those based on rotating-wall bioreactors, will increasingly be used and represent a more reproducible alternative to in-flight experiments. These low-shear vessels also make three-dimensional cellular co-cultures possible and thus allow to study the gravisensitivity of radioresponse in a context that better mimics cell-to-cell communication and hence in vivo cellular behavior.

Cell Communication↗

PubMed2003

Effects of strength training, using a gravity-independent exercise system, performed during 110 days of simulated space station confinement.

The efficacy of a resistance exercise paradigm, using a gravity-independent flywheel principle, was examined in four men subjected to 110 days of confinement (simulation of flight of international crew on space station; SFINCSS-99). Subjects performed six upper- and lower-body exercises (calf raise, squat, back extension, seated row, lateral shoulder raise, biceps curl) 2-3 times weekly during the confinement. The exercise regimen consisted of four sets of ten repetitions of each exercise at estimated 80-100% of maximal effort. Work was measured and recorded in each exercise session. Maximal voluntary isometric force in the calf press, squat and back extension, was assessed at three different joint angles before and after confinement. Overall, the training load (work) increased in all subjects (range 16-108%) over the course of the intervention. Maximal voluntary isometric force was unchanged following confinement. Although the perceived level of strain and comfort varied between exercises and among individuals, the results of the present study suggest this resistance exercise regimen is effective in maintaining or even increasing performance and maximal force output during long-term confinement. These findings should be considered in the design of resistance exercise hardware and prescriptions to be employed on the International Space Station.

Adaptation, Physiological↗

PubMed2003

Gravity-induced modification of auxin transport and distribution for peg formation in cucumber seedlings: possible roles for CS-AUX1 and CS-PIN1.

Cucurbit seedlings potentially develop a peg on each side of the transition zone between the hypocotyl and root. Seedlings grown in a horizontal position suppress the development of the peg on the upper side of the transition zone in response to gravity. It is suggested that this suppression occurs due to a reduction in auxin levels to below the threshold value. We show in this study that the free indole-3-acetic acid (IAA) content is low, while IAA conjugates are significantly more abundant in the upper side of the transition zone of gravistimulated seedlings, compared to the lower side. A transient increase in mRNA of the auxin-inducible gene, CS-IAA1, was observed in the excised transition zone. The result suggests that the transition zone is a source of auxin. Cucumber seedlings treated with auxin-transport inhibitors exhibited agravitropic growth and developed a peg on each side of the transition zone. Auxin-transport inhibitors additionally caused an increase in CS-IAA1 mRNA accumulation at the transition zone, indicating a rise in intracellular auxin concentrations due to a block of auxin efflux. To study the involvement of the auxin transport system in peg formation, we isolated the cDNAs of a putative auxin influx carrier, CS-AUX1, and putative efflux carrier, CS-PIN1, from cucumber (Cucumis sativus L.) plants. Both genes (CS-AUX1 in particular) were auxin-inducible. Accumulation of CS-AUX1 and CS-PIN1 mRNAs was observed in vascular tissue, cortex and epidermis of the transition zone. A reduced level of CS-AUX1 mRNA was observed in the upper side of the gravistimulated transition zone, compared with the lower side. It is therefore possible that a balance in the activities of auxin influx and efflux carriers controls intracellular auxin concentration at the transition zone, which results in lateral placement of a peg in cucumber seedlings.

Arabidopsis Proteins↗

PubMed2003

Gravity susception by buoyancy: floating lipid globules in sporangiophores of Phycomyces.

To elucidate the mechanisms of gravity susception that operate in the sporangiophore of Phycomyces blakesleeanus, we characterized the function and topography of a large apical complex of lipid globules. Stage-1 sporangiophores (without sporangium) possess a roughly spherical complex of 100-200 large lipid globules whose center is localized 110 microm below the apex. The complex of lipid globules (CLG) is rather stable and is kept in place by positioning forces that resist centrifugal accelerations of up to 150 g. The lipid globules possess an average diameter of 2 to 2.5 microm and a density of 0.791 g cm(-3), which is below that of typical plant oleosomes. The potential energy which is generated by the buoyancy of a CLG of 100 globules is in the order of 10(-17) to 10(-16) J, which is 4 to 5 orders of magnitude above thermal noise. The formation of lipid globules can be suppressed by raising stage-1 sporangiophores for 24 hs at 5 degrees C. Sporangiophores with a reduced number of lipid globules display gravitropic bending angles that are 3 to 4 times smaller than those of sporangiophores with the normal number of lipid globules. The results suggest that the lipid globules function as gravisusceptors of Phycomyces and that buoyancy is the physical principle for their mode of action. The globules contain beta-carotene and two distinct fluorescing pigments that are, however, dispensable for graviperception.

Gravitropism↗

PubMed2000

The auxin-resistant diageotropica mutant of tomato responds to gravity via an auxin-mediated pathway.

Hypocotyls of the diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) do not elongate in response to exogenous auxin, but can respond to gravity. This appears paradoxical in light of the Cholodny-Went hypothesis, which states that shoot gravicurvature results from asymmetric stimulation of elongation by auxin. While light-grown dgt seedlings can achieve correct gravitropic reorientation, the response is slow compared to wild-type seedlings. The sensitivity of dgt seedlings to inhibition of gravicurvature by immersion in auxin or auxin-transport inhibitors is similar to that of wild-type plants, indicating that both an auxin gradient and auxin transport are required for the gravitropic response and that auxin uptake, efflux, and at least one auxin receptor are functional in dgt. Furthermore, dgt gravicurvature is the result of asymmetrically increased elongation as would be expected for an auxin-mediated response. Our results suggest differences between elongation in response to exogenous auxin (absent in dgt) and elongation in response to gravistimulation (present but attenuated in dgt) and confirm the presence of two phases during the gravitropic response, both of which are dependent on functional auxin transport.

Benzoic Acid↗

PubMed2000

Spatial memory averaging, the landmark attraction effect, and representational gravity.

The effect of a large stationary landmark on memory for the location of a stationary target was examined. Memory for a stationary target was displaced toward the landmark, and targets that were larger, further from, or above the landmark exhibited greater magnitudes of displacement. Displacement was generally larger when the landmark vanished prior to judgment than when the landmark was visible during judgment. Memory for stationary targets offset from the major vertical or horizontal cardinal axis of the landmark was also displaced toward that cardinal axis. The data support the hypotheses that spatial memory averaging of the locations of a target and landmark occurs, and that this averaging may be combined with representational gravity in determining the remembered position of a stationary target.

Humans↗

PubMed2000

Retroperitoneoscopic nephrectomy (RN): using the gravity technique to facilitate specimen entrapment.

BACKGROUND: Kidney entrapment is generally considered to be a difficult step in retroperitoneoscopic nephrectomy (RN). Normally, a large device is needed to accommodate the specimen, which may measure </=14 x 10 cm. There is just too little space to maneuver either the entrapment device or the specimen. Herein we describe a technique that can overcome this difficulty and even turn the space limitation to advantage. METHODS: After the nephrectomy, the specimen is pushed caudally. A 15-mm Endocatch is inserted via the posterior cranial port. It is positioned strategically underneath the specimen so that when the entrapment bag is released, the specimen will have no room to move (because of the limited space) and will simply fall into the bag (because of gravity). RESULTS: We have used this technique for our last four cases of retroperitoneoscopic nephrectomy and found that it remarkably shortened the operative time for this step. CONCLUSION: One of the criticisms leveled against retroperitoneoscopic surgery concerns the problems posed by the space limitation. This technique turns the space limitation into an advantage and guarantees successful specimen entrapment.

Gravitation↗

PubMed2004

Is a specific oncological scoring system better at predicting the prognosis of cancer patients admitted for an acute medical complication in an intensive care unit than general gravity scores?

OBJECTIVE: To evaluate the effectiveness of a specific oncologic scoring system-the ICU Cancer Mortality model (ICM)-in predicting hospital mortality in comparison to two general severity scores-the Acute Physiology and Chronic Health Evaluation (APACHE II) and the Simplified Acute Physiology Score (SAPS II). PATIENTS AND METHODS: All 247 patients admitted for a medical acute complication over an 18-month period in an oncological medical intensive care unit were prospectively registered. Their data, including type of complication, vital status at discharge and cancer characteristics as well as other variables necessary to calculate the three scoring systems were retrospectively assessed. RESULTS: Observed in-hospital mortality was 34%. The predicted in-hospital mortality rate for APACHE II was 32%; SAPS II, 24%; and ICM, 28%. The goodness of fit was inadequate except for the ICM score. Comparison of the area under the ROC curves revealed a better fit for ICM (area 0.79). The maximum correct classification rate was 72% for APACHE II, 74% for SAPS II and 77% for ICM. APACHE II and SAPS II were better at predicting outcome for survivors to hospital discharge, although ICM was better for non-survivors. Two variables were independently predicting the risk of death during hospitalisation: ICM (OR=2.31) and SAPS II (OR=1.05). CONCLUSIONS: Gravity scores were the single independent predictors for hospital mortality, and ICM was equivalent to APACHE II and SAPS II.

APACHE↗

PubMed2005

A quantitative survey of gravity receptor function in mutant mouse strains.

The purpose of this research was to identify vestibular deficits in mice using linear vestibular evoked potentials (VsEPs). VsEP thresholds, peak latencies, and peak amplitudes from 24 strains with known genetic mutations and 6 inbred background strains were analyzed and descriptive statistics generated for each strain. Response parameters from mutant homozygotes were compared with heterozygote and/or background controls and all strain averages were contrasted to normative ranges. Homozygotes of the following recessive mutations had absent VsEPs at the ages tested: Espn(je), Atp2b2dfw-2J, Spnb4qv-lnd2J, Spnb4qv-3J, Myo7ash1, Tmie(sr), Myo6sv, jc, Pcdh15av-J, Pcdh15av-2J, Pcdh15av-3J, Cdh23v-2J, Sans(js), hr, Kcne1pkr and Pou3f4del. These results suggest profound gravity receptor deficits for these homozygotes, which is consistent with the structural deficits that have been documented for many of these strains. Homozygotes of Catna2cdf, Grid2ho4J, Wnt1sw, qk, and Mbpshi strains and heterozygotes of Grid2lc had measurable VsEPs but one or more response parameters differed from the respective control group (heterozygote or background strain) or were outside normal ranges. For example, qk and Mbpshi homozygotes showed significantly prolonged latencies consistent with the abnormal myelin that has been described for these strains. Prolonged latencies may suggest deficits in neural conduction; elevated thresholds suggest reduced sensitivity, and reduced amplitudes may be suggestive for reduced neural synchrony. One mutation, Otx1jv, had all VsEP response parameters within normal limits--an expected finding because the abnormality in Otxljv is presumably restricted to the lateral semicircular canal. Interestingly, some heterozygote groups also showed abnormalities in one or more VsEP response parameters, suggesting that vestibular dysfunction, although less severe, may be present in some heterozygous animals.

Animals↗

PubMed1986

Gravity-flow alkaline elution: a method to rapidly detect carcinogen-induced DNA strand breaks.

A rapid, sensitive and reliable gravity-flow alkaline elution assay was developed to detect DNA strand breaks in cultured Madin-Darby bovine kidney epithelial cells. Elution was completed within 2 h without the use of pumps. The system was validated by exposing the cells to X-irradiation (25-1500 R) which resulted in a significant dose dependent response (p less than 0.05) with excellent correlation (r-0.93). The assay reliably detected the DNA damage of seven genotoxic carcinogens. In general, the measured DNA damage was dose dependent and significantly different from control values for all genotoxic carcinogens tested. Six non-genotoxic compounds were tested and showed no detectable DNA damage.

Animals↗

PubMedDate not supplied

Migration of human granulocytes in filters: effects of gravity and movable gradients of f-MLP.

The Boyden chamber technique for chemotaxis uses a mesh filter that constitutes a matrix for cell locomotion and, at the same time, creates a local restriction for convective fluid movements that allows the establishment of a diffusive concentration gradient of chemotactic substance in the filter. In the present study, the Boyden chamber was modified by the introduction of a filter sandwich that allowed cell migration both upwards and downwards and by the use of a fluid density gradient controlling cell buoyancy and mechanically supporting a movable chemotactic gradient. This method was used to study chemotaxis and random migration of human granulocytes under the influence of gravitational forces and movable gradients of f-MLP. The results show that gravity affected cell motion significantly during random migration but not during chemotaxis. The rate of chemotactic migration was dependent on the steepness of the spatio-temporal f-MLP gradients. A stationary spatial gradient produced less migration than a gradient that was slowly moved through the filter sandwich in a direction opposite to that of the cell migration. The presence of f-MLP at constant concentration caused a minor, statistically insignificant, increase of the rate of random migration.

Cell Movement↗

PubMed1979

Hair cell polarization in the gravity receptor systems of the statocysts of the cephalopods Sepia officinalis and Loligo vulgaris.

The complete patterns of polarization of the sensory epithelia of the various gravity receptor systems of the decapods Sepia and Loligo have been described (Fig. 6). Each individual receptor cell (hair cell) bears up to 150 kinocilia, but is polarized unidirectionally by 3 morphological features: (I) by the orientation of the internal 9X2+2 tubuli structure of each kinocilium, (II) by the location of their basal feet. Each hair cell is additionally polarized (III), in that its kinociliary group is inclined toward the plane of the macula surface, forming an angle of 40-60 degrees with it (Figs. 1-3); the direction of polarization, as given by the ultrastructural features (I and II), is always opposite to this acute angle (Fig. 4). The results are discussed with reference to their physiological consequences.

Acoustic Maculae↗

PubMed1978

Binding of the chemical carcinogen N-hydroxy-acetyl-aminofluorene to ploidy classes of rat liver nuclei as separated by velocity sedimentation at unit gravity.

A large sedimentation device was developed that allows separation of 5 X 10(8) rat liver nuclei by velocity sedimentation at unit gravity. Using the apparatus isolated rat liver nuclei were separated into classes of diploid stromal (Von Kuppfer, sinusoidal lining) nuclei, diploid parenchymal nuclei and tetraploid parenchymal nuclei respectively. DNA content and volume of the nuclei were measured. Diploid nuclei were 100% pure; tetraploid nuclei 98%. The in vivo binding of the liver carcinogen [3H]-N-hydroxy-AAF to these classes of nuclei was determined (total binding to protein, DNA and RNA). Binding and the subsequent removal of the fluorene derivatives was registered as a function of time. At all stages diploid stromal nuclei bound 2.6--5 times less carcinogen than did diploid parenchymal nuclei. Tetraploid parenchymal nuclei bound more than twice (2.3--3.95) the amount, that was present in their diploid counterpart. This effect became more pronounced 11 days after application of N-hydroxy-N-acetyl-2-aminofluorene. DNA was enzymatically purified from pooled classes of the various nuclear types. For purified DNA also it was found that DNA derived from diploid stromal nuclei bound 2.6--2.8 times less carcinogen than did DNA derived from diploid parenchymal nuclei.

Animals↗

PubMed1994

The role of gravity in chick embryogenesis.

Thirty fertilized chick eggs preincubated for 0, 7 and 10 days on earth (10 eggs each) were flown in the space shuttle 'Endeavour' and further incubated for 7 days under microgravity. Twenty out of thirty eggs (9/10 ten-day-old; 10/10 seven-day-old; 1/10 zero-day-old) were recovered alive after landing. The only living embryo of the zero-day-old group died 24 days after launch, and was comparable to a 16-day-old embryo. The high mortality of the 0-day-old eggs appeared to be related to the specific inner structure of the egg. Simulation experiments performed on earth indicated that when yolk stayed in the albumen for more than 2 days, most of the embryos died. The subtle difference in specific gravity between the yolk (1.029) and albumen (1.040) plays a critical role in early chick embryogenesis.

Animals↗