Changes in Doppler mitral inflow patterns during parabolic flight

Aim of the study was to evaluate by transthoracic Doppler the alterations in mitral inflow velocity pattern caused by acute changes in loading conditions occurring during parabolic flights. Each parabola included normogravity (1 Gz, 1 min), mild hypergravity (1.8 Gz, 20 sec), microgravity (0 Gz, 24 sec) and mild hypergravity (1.8 Gz, 20 sec) phases. Pulsed-Doppler images were digitally acquired in 11 unmedicated subjects (46 +/- 5 years), in standing upright position and supine resting. Doppler profiles were semi-automatically traced and inflow parameters extracted and averaged onto three consecutive beats. Only in standing position, significant alterations during microgravity (p<0.05) were noted in several parameters.     

Physiological parameters of gravitaxis in the flagellate Euglena gracilis obtained during a parabolic flight campaign

The unicellular freshwater flagellate Euglena gracilis and its close relative Astasia longa show a pronounced negative gravitaxis. Previous experiments revealed that gravitaxis is most likely mediated by an active physiological mechanism in which changes of the internal calcium concentration and the membrane potential play an important role. In a recent parabolic flight experiment on board an aircraft (ESA 29th parabolic flight campaign), changes of graviorientation, membrane potential and the cytosolic calcium concentration upon changes of the acceleration (between 1 x g(n), 1.8 x g(n), microgravity) were monitored by image analysis and photometric methods using Oxonol VI (membrane potential) and Calcium Crimson (cytosolic calcium concentration). The parabolic flight maneuvers performed by the aircraft resulted in transient phases of 1.8 x g(n) (about 20 s), microgravity (about 22 s) followed by 1.8 x g(n) (about 20 s). A transient increase in the intracellular calcium concentration was detected from lower to higher accelerations (1 x g(n) to 1.8 x g(n) or microgravity to 1.8 x g(n)). Oxonol VI-labeled cells showed a signal, which indicates a depolarization during the transition from 1 x g(n) to 1.8 x g(n), a weak repolarization in microgravity followed by a rapid repolarization in the subsequent 1 x g(n) phase. The results show good coincidence with observations of recent terrestrial and space experiments.     

How to activate a plant gravireceptor. Early mechanisms of gravity sensing studied in characean rhizoids during parabolic flights

Early processes underlying plant gravity sensing were investigated in rhizoids of Chara globularis under microgravity conditions provided by parabolic flights of the A300-Zero-G aircraft and of sounding rockets. By applying centrifugal forces during the microgravity phases of sounding rocket flights, lateral accelerations of 0.14 g, but not of 0.05 g, resulted in a displacement of statoliths. Settling of statoliths onto the subapical plasma membrane initiated the gravitropic response. Since actin controls the positioning of statoliths and restricts sedimentation of statoliths in these cells, it can be calculated that lateral actomyosin forces in a range of 2 x 10(-14) n act on statoliths to keep them in place. These forces represent the threshold value that has to be exceeded by any lateral acceleration stimulus for statolith sedimentation and gravisensing to occur. When rhizoids were gravistimulated during parabolic plane flights, the curvature angles of the flight samples, whose sedimented statoliths became weightless for 22 s during the 31 microgravity phases, were not different from those of in-flight 1g controls. However, in ground control experiments, curvature responses were drastically reduced when the contact of statoliths with the plasma membrane was intermittently interrupted by inverting gravistimulated cells for less than 10 s. Increasing the weight of sedimented statoliths by lateral centrifugation did not enhance the gravitropic response. These results provide evidence that graviperception in characean rhizoids requires contact of statoliths with membrane-bound receptor molecules rather than pressure or tension exerted by the weight of statoliths.     

Cardiovascular adaptations to parabolic flight in rats: a radio-telemetry feasibility study

This experiment was a feasibility study which consisted in investigating arterial blood pressure and heart rate to transient and repeated exposure to microgravity in eight unrestrained rats previously implanted with radio-telemetry transmitter. The aim was to perform such recordings throughout all the phases of a parabola during parabolic flights. This study revealed that it was possible to collect the radio-signal without any interference with electronic or magnetic environment. We observed in microgravity a significant reduction in heart rate (6%) and a significant increase in arterial blood pressure (7%). In conclusion, such a study seems to be feasible during longer exposure to microgravity (space flight) in order to study the cardiovascular adaptation in rat.     

Rapid alterations of cell cycle control proteins in human T lymphocytes in microgravity

ABSTRACT: In our study we aimed to identify rapidly reacting gravity-responsive mechanisms in mammalian cells in order to understand if and how altered gravity is translated into a cellular response. In a combination of experiments using "functional weightlessness" provided by 2D-clinostats and real microgravity provided by several parabolic flight campaigns and compared to in-flight-1g-controls, we identified rapid gravity-responsive reactions inside the cell cycle regulatory machinery of human T lymphocytes. In response to 2D clinorotation, we detected an enhanced expression of p21 Waf1/Cip1 protein within minutes, less cdc25C protein expression and enhanced Ser147-phosphorylation of cyclinB1 after CD3/CD28 stimulation. Additionally, during 2D clinorotation, Tyr-15-phosphorylation occurred later and was shorter than in the 1 g controls. In CD3/CD28-stimulated primary human T cells, mRNA expression of the cell cycle arrest protein p21 increased 4.1-fold after 20s real microgravity in primary CD4+ T cells and 2.9-fold in Jurkat T cells, compared to 1 g in-flight controls after CD3/CD28 stimulation. The histone acetyltransferase (HAT) inhibitor curcumin was able to abrogate microgravity-induced p21 mRNA expression, whereas expression was enhanced by a histone deacetylase (HDAC) inhibitor. Therefore, we suppose that cell cycle progression in human T lymphocytes requires Earth gravity and that the disturbed expression of cell cycle regulatory proteins could contribute to the breakdown of the human immune system in space.     

The effects of a change in gravity on the dynamics of prehension

The objective of this study was to measure the forces applied on an object manipulated in different gravitational fields attained during parabolic flights. Eight subjects participated flights (ES) and four were inexperienced (NES). They had to move continuously an instrumented object up and down in three different gravitational conditions (1 g, 1.8 g, 0 g). In 1 g, the grip force precisely anticipated the fluctuations of load force which was maximum and minimum at the bottom and at the top of the arm trajectory respectively. When the gravity changed (0 g and 1.8 g), the grip-load force coupling persisted for all the subjects from the first parabola. While the ES immediately exerted a grip force appropriate to the gravity, the NES dramatically increased their grip when faced with hyper and microgravity for the first time. Then, they progressively released their grip until a continuous grip-load force relationship with regard to 1 g was established after the fifth parabola. We suggest that each new gravitational field is rapidly incorporated into an internal model within the CNS which can then be reused as required by the occasion.     

Influence of gravity changes induced by parabolic flight on cytokine production in mouse spleen

Dysregulation of the immune system has been a well-documented effect of human exposure to a microgravity environment during space flight. These effects have included altered cytokine production, reduced proliferative responses, altered signal transduction pathways and altered distribution of peripheral immune cells. Recent reports have documented immunologic studies performed in-flight. When tested during space flight, delayed-type hypersensitivity was reduced, indicating a dysregulation of cell-mediated immune function. However, the mechanisms by which this occurs remain unclear. The production of cytokines plays a critical role in the ability of a host to mount an immune response against an invading microorganism. In this study, the alteration of cytokine responses in mice following parabolic flight (PF) was investigated.     

Effects of spaceflight on human calf hemodynamics.

Chronic microgravity may modify adaptations of the leg circulation to gravitational pressures. We measured resting calf compliance and blood flow with venous occlusion plethysmography, and arterial blood pressure with sphygmomanometry, in seven subjects before, during, and after spaceflight. Calf vascular resistance equaled mean arterial pressure divided by calf flow. Compliance equaled the slope of the calf volume change and venous occlusion pressure relationship for thigh cuff pressures of 20, 40, 60, and 80 mmHg held for 1, 2, 3, and 4 min, respectively, with 1-min breaks between occlusions. Calf blood flow decreased 41% in microgravity (to 1.15 +/- 0.16 ml x 100 ml(-1) x min(-1)) relative to 1-G supine conditions (1.94 +/- 0.19 ml x 100 ml(-1) x min(-1), P = 0.01), and arterial pressure tended to increase (P = 0.05), such that calf vascular resistance doubled in microgravity (preflight: 43 +/- 4 units; in-flight: 83 +/- 13 units; P < 0.001) yet returned to preflight levels after flight. Calf compliance remained unchanged in microgravity but tended to increase during the first week postflight (P > 0.2). Calf vasoconstriction in microgravity qualitatively agrees with the "upright set-point" hypothesis: the circulation seeks conditions approximating upright posture on Earth. No calf hemodynamic result exhibited obvious mechanistic implications for postflight orthostatic intolerance.     

Behavior of Medaka fish under distributed gravity.

The threshold value of gravity for Medaka fish (Oryzias latipes) was determined using parabolic flights of an airplane. Rotating a turntable during a 20 sec of microgravity, a gradient field of centrifugal force was realized in the aquarium. Fish of HO5 strain were used because from the previous studies, in microgravity they were known to exhibit looping behavior more easily than any other strains. Looping fish became stable (i.e., recovered their posture control) when fish swam from a lower-gravity area of the aquarium to an area of a certain gravity value or beyond. On the other hand, stable fish lost their posture control and started looping when fish swam into an area of a gravity lower than a certain value. Using these phenomena, we obtained the gravity value of 0.21 to 0.26 G as for the threshold value for Medaka fish to sense the gravity.     

Bacterial Cellulose-Binding Domain Modulates in Vitro Elongation of Different Plant Cells

Recombinant cellulose-binding domain (CBD) derived from the cellulolytic bacterium Clostridium cellulovorans was found to modulate the elongation of different plant cells in vitro. In peach (Prunus persica L.) pollen tubes, maximum elongation was observed at 50 μg mL⁻¹ CBD. Pollen tube staining with calcofluor showed a loss of crystallinity in the tip zone of CBD-treated pollen tubes. At low concentrations CBD enhanced elongation of Arabidopsis roots. At high concentrations CBD dramatically inhibited root elongation in a dose-responsive manner. Maximum effect on root hair elongation was at 100 μg mL⁻¹, whereas root elongation was inhibited at that concentration. CBD was found to compete with xyloglucan for binding to cellulose when CBD was added first to the cellulose, before the addition of xyloglucan. When Acetobacter xylinum L. was used as a model system, CBD was found to increase the rate of cellulose synthase in a dose-responsive manner, up to 5-fold compared with the control. Electron microscopy examination of the cellulose ribbons produced by A. xylinum showed that CBD treatment resulted in a splayed ribbon composed of separate fibrillar subunits, compared with a thin, uniform ribbon in the control.     

Type 5 adenylyl cyclase plays a major role in stabilizing heart rate in response to microgravity induced by parabolic flight.

It is well known that autonomic nervous activity is altered under microgravity, leading to disturbed regulation of cardiac function, such as heart rate. Autonomic regulation of the heart is mostly determined by beta-adrenergic receptors/cAMP signal, which is produced by adenylyl cyclase, in cardiac myocytes. To examine a hypothesis that a major cardiac isoform, type 5 adenylyl cyclase (AC5), plays an important role in regulating heart rate during parabolic flights, we used transgenic mouse models with either disrupted (AC5KO) or overexpressed AC5 in the heart (AC5TG) and analyzed heart rate variability. Heart rate had a tendency to decrease gradually in later phases within one parabola in each genotype group, but the magnitude of decrease was smaller in AC5KO than that in the other groups. The inverse of heart rate, i.e., the R-R interval, was much more variable in AC5KO and less variable in AC5TG than that in wild-type controls. The standard deviation of normal R-R intervals, a marker of total autonomic variability, was significantly greater in microgravity phase in each genotype group, but the magnitude of increase was much greater in AC5KO than that in the other groups, suggesting that heart rate regulation became unstable in the absence of AC5. In all, AC5 plays a major role in stabilizing heat rate under microgravity.     

Gravity effects on regional lung ventilation determined by functional EIT during parabolic flights.

Gravity-dependent changes of regional lung function were studied during normogravity, hypergravity, and microgravity induced by parabolic flights. Seven healthy subjects were followed in the right lateral and supine postures during tidal breathing, forced vital capacity, and slow expiratory vital capacity maneuvers. Regional 1) lung ventilation, 2) lung volumes, and 3) lung emptying behavior were studied in a transverse thoracic plane by functional electrical impedance tomography (EIT). The results showed gravity-dependent changes of regional lung ventilation parameters. A significant effect of gravity on regional functional residual capacity with a rapid lung volume redistribution during the gravity transition phases was established. The most homogeneous functional residual capacity distribution was found at microgravity. During vital capacity and forced vital capacity in the right lateral posture, the decrease in lung volume on expiration was larger in the right lung region at all gravity phases. During tidal breathing, the differences in ventilation magnitudes between the right and left lung regions were not significant in either posture or gravity phase. A significant nonlinearity of lung emptying was determined at normogravity and hypergravity. The pattern of lung emptying was homogeneous during microgravity.     

Enzyme catalysis in microgravity: steady-state kinetic analysis of the isocitrate lyase reaction

Two decades of research in microgravity have shown that certain biochemical processes can be altered by weightlessness. Approximately 10 years ago, our team, supported by the European Space Agency (ESA) and the Agenzia Spaziale Italiana, started the Effect of Microgravity on Enzyme Catalysis project to test the possibility that the microgravity effect observed at cellular level could be mediated by enzyme reactions. An experiment to study the cleavage reaction catalyzed by isocitrate lyase was flown on the sounding rocket MASER 7, and we found that the kinetic parameters were not altered by microgravity. During the 28th ESA parabolic flight campaign, we had the opportunity to replicate the MASER 7 experiment and to perform a complete steady-state analysis of the isocitrate lyase reaction. This study showed that both in microgravity and in standard g controls the enzyme reaction obeyed the same kinetic mechanism and none of the kinetic parameters, nor the equilibrium constant of the overall reaction were altered. Our results contrast with those of a similar experiment, which was performed during the same parabolic flight campaign, and showed that microgravity increased the affinity of lipoxygenase-1 for linoleic acid. The hypotheses suggested to explain this change effect of the latter were here tested by computer simulation, and appeared to be inconsistent with the experimental outcome.     

Effects of gravitropic stress on the development of the primary root of lentil seedlings grown in space

Root growth and cell differentiation were analysed in lentil seedlings grown (1) in microgravity (F microg), (2) on the 1 x g centrifuge (F1 x g), (3) in microgravity and placed on the 1 x g centrifuge for 4 h [F(microg + 1 x g)], (4) on the 1 x g centrifuge and placed in microgravity for 4 h [F(1 x g + microg)]. In microgravity, there were strong oscillations of the root tip, even when the seedlings were grown first on the 1 x g centrifuge [F(1 x g + microg)]. In the [F(microg + 1 x g)] sample, the roots grown in microgravity were oblique with respect to the 1 x g acceleration when the seedlings were placed on the centrifuge. They were therefore gravistimulated. However, root length was similar in the 4 samples after 29 h of growth and growth rate of the root was the same between 25 h and 29 h although it appeared to be slightly greater in the [F(microg + 1 x g)] sample. Cell elongation was analysed as a function of the distance from the root cap junction. Cell length was similar in the seedlings grown in microgravity or on the 1 x g centrifuge. The transfer from the 1 x g centrifuge to microgravity [F(1 x g + microg)] did not modify cell elongation in the roots. Cell length in the roots which were grown in microgravity and gravistimulated [F(microg + 1 x g)] was different from that observed in microgravity but this was only due to gravistimulation. Thus, gravity does not have an effect on cell elongation when the roots are strictly oriented in the vertical position but it does as soon as the root tip deviates from this orientation.     

不同培养方式对细菌纤维素产量和结构性质的影响

考察了自行筛选的Acetobacter xylinum NUST4.2在静置培养和发酵罐培养获得的细菌纤维素(BC)的产量、基本结构和性能的差异。结果表明:静置培养时产纤维素7.5g/L,产率为0.052g/L/h,在机械搅拌发酵罐中培养3d产量达3.13g/L,产率达0.043g/L/h;SEM分析显示静置培养和发酵罐培养得到的纤维素均具有网状结构,但静置获得的纤维素丝带相互缠绕且层状重叠,更加致密,丝带更细;FT-IR分析知搅拌不改变纤维素的化学结构,但能减弱分子间氢键,和XRD结合分析可知静置培养的纤维素具有更高结晶指数,更高Iα含量和更大晶粒尺寸,但不改变晶型,仍为纤维素I型,说明搅拌会干扰纤维素初始纤丝的结晶,有利于形成更小的晶粒和较Iα稳定的Iβ。与棉纤维素相比,静置培养获得的纤维素的热稳定性更好,而发酵罐培养获得的纤维素则阻燃性更好。     

Responses to hypergravity in proliferation of Paramecium tetraurelia

It has been reported that Paramecium proliferates faster when cultured under microgravity in orbit, and slower when cultured under hypergravity. This shows that the proliferation rate of Paramecium affected by gravity. The effect of gravity on Paramecium proliferation has been argued to be direct in a paper with an axenic culture under hypergravity. To clear up uncertainties with regard to the effect of gravity, Paramecium tetraurelia was cultured axenically under hypergravity (20 x g) and the time course of the proliferation was investigated quantitatively by a new non-invasive method, laser-beam optical slice, for measuring the cell density. This method includes optical slicing a part of the culture and computer-aided counting of cells in the sliced volume. The effects of hypergravity were assessed by comparing the kinetic parameters of proliferation that were obtained through a numerical analysis based on the logistic growth equation. Cells grown under 20 x g conditions had a significantly lower proliferation rate, and had a lower population density at the stationary phase. The lowered proliferation rate continued as long as cells were exposed to hypergravity (> one month). Hypergravity reduced the cell size of Paramecium. The long and short axes of the cell became shorter at 20 x g than those of control cells, which indicates a decrease in volume of the cell grown under hypergravity and is consistent with the reported increase in cell volume under microgravity. The reduced proliferation rate implies changes in biological time defined by fission age. In fact the length of autogamy immaturity decreased by measure of clock time, whereas it remained unchanged by measure of fission age.     

Optospectroscopic detection of primary reactions associated with the graviperception of Phycomyces. Effects of micro- and hypergravity

The graviperception of sporangiophores of the fungus Phycomyces blakesleeanus involves gravity-induced absorbance changes (GIACs) that represent primary responses of gravitropism (Schmidt and Galland, 2000). GIACs (DeltaA(460-665)) of sporangiophores were measured in vivo with a micro-dual wavelength spectrometer at 460 and 665 nm. Sporangiophores that were placed horizontally displayed an instant increase of the GIACs while the return to the vertical position elicited an instant decrease. The GIACs are specific for graviperception, because they were absent in a gravitropism mutant with a defective madJ gene. During parabola flights hypergravity (1.8 g) elicited a decrease of the GIACs, while microgravity (0 +/- 3 x 10 (-2) g) elicited an instant increase. Hypergravity that was generated in a centrifuge (1.5-6.5 g) elicited also a decrease of the GIACs that saturated at about 5 g. The GIACs have a latency of about 20 ms or shorter and are thus the fastest graviresponses ever measured for fungi, protists, and plants. The threshold for eliciting the GIACs is near 3 x 10 (-2) g, which coincides numerically with the threshold for gravitropic bending. In contrast to gravitropic bending, which requires long-term stimulation, GIACs can be elicited by stimuli as short as 20 to 100 ms, leading to an extremely low threshold dose (acceleration x time) of about 3 x 10 (-3) g s, a value, which is four orders of magnitude below the ones described for other organisms and which makes the GIACs of Phycomyces blakesleeanus the most sensitive gravi-response in literature.     

Statoliths pull on microfilaments

Summary Previous videomicroscopy ofChara rhizoids during parabolic flights of rockets showed that the weightless statoliths moved basipetally. A hypothesis was offered that the removal of gravity force disturbed the initial balance between this force and the basipetally acting forces generated in a dynamic interaction of statoliths with microfilaments (MFs). The prediction of this hypothesis that the statoliths would not be displaced basipetally during the microgravity phase (MG-phase) after disorganizing the MFs was tested by videomicroscopy of a rhizoid treated with cytochalasin D (CD) immediately before the flight. The prediction was fully supported by the flight experiment. Additionally, by chemical fixation of many rhizoids at the end of the MG-phase it was shown that all rhizoids treated with CD before the flight had statoliths at the same location, i.e., sedimented on the apical cell wall, while all untreated rhizoids had statoliths considerably displaced basipetally from their normal position. Thus, a dynamical interaction involving shearing forces between MFs and statoliths appears highly probable.Abbreviations CD cytochalasin D - g gravitational acceleration - MF microfilament - MG-phase microgravity phase - TEXUS technological experiments under reduced gravity Dedicated to Hilton H. Mollenhauer on the occasion of his retirement     

Shift in arm-pointing movements during gravity changes produced by aircraft parabolic flight.

It has been shown that target-pointing arm movements without visual feedback shift downward in space microgravity and upward in centrifuge hypergravity. Under gravity changes in aircraft parabolic flight, however, arm movements have been reported shifting upward in hypergravity as well, but a downward shift under microgravity is contradicted. In order to explain this discrepancy, we reexamined the pointing movements using an experimental design which was different from prior ones. Arm-pointing movements were measured by goniometry around the shoulder joint of subjects with and without eyes closed or with a weight in the hand, during hyper- and microgravity in parabolic flight. Subjects were fastened securely to the seat with the neck fixed and the elbow maintained in an extended position, and the eyes were kept closed for a period of time before each episode of parabolic flight. Under these new conditions, the arm consistently shifted downward during microgravity and mostly upward during hypergravity, as expected. We concluded that arm-pointing deviation induced by parabolic flight could be also be valid for studying the mechanism underlying disorientation under varying gravity conditions.     

Endocytosis in tobacco pollen tubes: visualisation and measurement of plasma membrane retrieval during different gravity conditions indicates gravity-dependence of endocytosis

We studied the effect of microgravity on endocytosis in growing tobacco pollen tubes by measuring the plasma membrane retrieval employing the fluorescent phospholipid bis-Bodipy FL C11- phosphatidylcholine as marker. Time course experiments under 1xg condition revealed a localised and relatively fast plasma membrane retrieval in the pollen tube tip region within the first minutes after lipid application. The rate of endocytotic bis-Bodipy FL C11- PC-modified plasma membrane retrieval is inhibited by hyper-g conditions achieved by centriftigal forces. In contrast, during the microgravity phase of a parabolic rocket flight the retrieval of the fluorescently-marked plasma membrane is distinctly enhanced. Our results show that microgravity exerts an unspecific physiological response in pollen tubes, most likely involving the cytoskeleton as inhibitor experiments indicate under 1xg condition.