Circadian rhythms of salivary cortisol content during long-term space flight

Adaptation mechanisms of adrenal function related to secretion of cortisol were studied under conditions of microgravity. Parameters of diurnal rhythms of salivary cortisol were studied by Russian cosmonauts on board orbital station Mir during long-term space flights (SF). The preflight circadian rhythms of salivary cortisol in cosmonauts were characterized by the morning maximum occurring at 9∶43 a.m., the fluctuation amplitude 6.05 nmol/1, and the daily average concentration 8.79 nmol/l. The characteristics of cortisol diurnal rhythm changed under conditions of long-term space flight. On average, the rhythm measure and amplitude decreased after two months of flight. The postflight maximum concentration of free cortisol tended to occur later in the day. Evidently, the motor activity during SF, i.e., prophylactic exercises along with other factors, significantly influenced the parameters of cortisol circadian rhythm that was revealed by the individual variability of findings during the flight. After the long-term SF, individual ratios of salivary and plasma cortisol levels increased against the background of increased plasma content of the hormone, i.e., the fraction of free, physiologically active hormone in the total pool of circulating molecules decreased.     

Phosphatidylethanolamine Is a Key Regulator of Membrane Fluidity in Eukaryotic Cells

Adequate membrane fluidity is required for a variety of key cellular processes and in particular for proper function of membrane proteins. In most eukaryotic cells, membrane fluidity is known to be regulated by fatty acid desaturation and cholesterol, although some cells, such as insect cells, are almost devoid of sterol synthesis. We show here that insect and mammalian cells present similar microviscosity at their respective physiological temperature. To investigate how both sterols and phospholipids control fluidity homeostasis, we quantified the lipidic composition of insect SF9 and mammalian HEK 293T cells under normal or sterol-modified condition. As expected, insect cells show minimal sterols compared with mammalian cells. A major difference is also observed in phospholipid content as the ratio of phosphatidylethanolamine (PE) to phosphatidylcholine (PC) is inverted (4 times higher in SF9 cells). In vitro studies in liposomes confirm that both cholesterol and PE can increase rigidity of the bilayer, suggesting that both can be used by cells to maintain membrane fluidity. We then show that exogenously increasing the cholesterol amount in SF9 membranes leads to a significant decrease in PE:PC ratio whereas decreasing cholesterol in HEK 293T cells using statin treatment leads to an increase in the PE:PC ratio. In all cases, the membrane fluidity is maintained, indicating that both cell types combine regulation by sterols and phospholipids to control proper membrane fluidity.     

Calcium metabolism and its regulation in man during adaptation to microgravitation

This work generalizes the results of studies of calcium metabolism in the participants of long-term space flights of 30 to 438 days on the Salyut and Mir orbital stations during 1978–1998. The results of pre- and postflight examination of 44 cosmonauts (18 subjects participated twice in long-term space flights) were analyzed. After space flights of medium (of 3 to 6 months) and long (of 6 to 14 months) duration, the total blood calcium content was increased, mainly due to its ionized fraction; the blood level of parathyroid hormone was significantly increased and the level of calcitonin was decreased. The content of osteocalcin was increased after space flights. Calcium kinetics was studied using stable isotopes in three cosmonauts before, during, and after the 115-day flight. During the flight, intestinal absorption of calcium and its gastrointestinal excretion were decreased, whereas its renal excretion was increased. Early postflight intestinal absorption was, on average, lower than during the flight, whereas intestinal excretion increased. Both renal and intestinal excretion of calcium were not normalized 3.5 to 4.5 months after the glight. The mathematical models used for evaluating the rates of main calcium flows revealed increased bone tissue resorption that resulted in the negative bone balance during the flight. The conclusion about the decreased rate of bone tissue remodeling and its increased resorption was confirmed by biochemical data, including endocrine markers.     

Exhaustive exercise affects fluidity and alpha-tocopherol levels in brain synaptosomal membranes of normal and vitamin E supplemented rats

Alpha-tocopherol level and fluidity were studied in the neuronal membrane of rat brain after exhaustive exercise. The order parameter, 5-doxyl-stearic acid (5-DS), which is utilized for assessing the fluidity of the lipid bilayer closer to the hydrophilic face of the membrane, decreased in the pons-medulla oblongata, and the motion parameter, 16-doxyl-stearic acid (16-DS) for the core of the lipid bilayer, decreased in the cortex, hippocampus, hypothalamus and striatum, whereas it increased in the cerebellum after exercise. The w/s ratio of n-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)-maleimido (maleimido-TEMPO) for the conformation of SH-protein also decreased in the hippocampus and midbrain after exercise. These changes were not observed in alpha-tocopheryl acetate supplemented rats after exercise. Although the levels of 5-DS, 16-DS and maleimido-TEMPO were affected by alpha-tocopheryl acetate in rat neuronal membranes, fluidity changes were reversible with exercise.     

Conformational transition and liquid crystalline state of regenerated silk fibroin in water

The conformational transition of molecular chains of regenerated silk fibroin (SF) aqueous solution is systematically investigated by circular dichroism, Raman, IR, and UV-vis spectroscopies. It is found that an initial random coil conformation of the SF can be readily changed into an ordered beta-sheet structure by optimizing the solution conditions, such as the SF concentration, pH, temperature, or metal-ion content. Circular dichroic spectra quantitatively confirm a steadily decreased content of the random coil conformation but a significantly increased beta-sheet content after an ultrasonic or extruding treatment. Furthermore, the extrusion is more powerful to achieve high beta-sheet content than the ultrasonic. It is interesting that the polarized optical micrographs of the SF aqueous solution extruded by injection illustrate the formation and existence of liquid crystalline state. A study of extrusion in vitro could be used as a model system to understand the natural silk spinning process in silkworm.     

Vestibular function and space motion sickness

The vestibular system plays an important role in intersensory interactions and gravitation is a natural stimulus for its receptors. Weightlessness alters the input signals of the otoliths and their effect on the pattern and dynamics of changes in the vestibular function (VF), which is accompanied by development of space adaptation syndrome (SAS) and space motion sickness (SMS). These changes occur both during the spaceflight (SF) and after returning to Earth, but the mechanisms of their development are still poorly understood and require special studies. In total, 47 Russian cosmonauts (crewmembers of long-term International Space Station (ISS) missions) have participated in the studies into VF before and after SF and nine of them, in onboard studies during SF (129–215 days) as a part of the Virtual space experiment (stage 1). Electro- and video-oculography are used to record spontaneous eye movements (SpEM), static vestibular–ocular responses during head tilts to the right or left shoulder (static otolith–cervical–ocular reflex, OCOR), and dynamic vestibular-ocular response during the head rotation around the longitudinal axis of the body. The examination is accompanied by personal and questionnaire survey on subjective responses and complaints of cosmonauts about SAS and SMS. Significant changes in SpEM (drifts of eyes, spontaneous and gaze-evoked nystagmus, and arbitrary saccades) and a decrease in OCOR (statistically significant decrease in the amplitude of ocular counter-rolling in response to head tilts up to its absence or inversion, an atypical OCOR) are observed during SF. An atypical OCOR is observed at the beginning of adaptation to weightlessness in seven of the nine cosmonauts (the first one to two weeks of SF) and repeatedly throughout the flight in all cosmonauts regardless of whether it is their first flight or not. Atypical vestibular responses after SF, similar to the responses during SF, are observed in several cosmonauts by day 9 after flight. It has been shown that atypical OCOR variants are more frequently observed in the subjects lacking any previous space experience, as well as a more pronounced decrease in this response with a concurrent increase in the response of the semicircular canals. It is also demonstrated that repeated SFs lead to a considerable shortening in the after-flight readaptation to terrestrial conditions and a considerable decrease in the degree of vestibular disorders. In the initial period of SF, the changes in VF are correlated with the complaints and manifestations of SAS and SMS; however, the complaints and the corresponding symptoms are unobservable during the further flight despite significant changes in the VF state. The patterns of the VF disorders associated with the impact of weightlessness and observed during and after SF are very similar, allowing these disorders to be regarded as SAS and SMS of different severities (intensities).     

Organization of membrane lipids and proteins in human En(a-) erythrocytes that lack the major sialoglycoprotein, glycophorin A. A spin-label study.

Membrane fluidity was studied by electron-spin-resonance techniques in human En(a-) erythrocytes that lack the major membrane sialoglycoprotein, glycophorin A. By using stearic acid spin labels with a doxyl group in the C-12 or C-15 positions, we demonstrated that the hydrophobic core in these cells was more fluid than in normal cells. Surface-located regions in isolated En(a-) membranes, when probed with stearic acid labelled in the C-5 position, appeared more stable than in normal membranes. In isolated En(a-) membranes, protein motion was decreased when probed with a nitroxide derivative of maleimide. After incubation with anti-(glycophorin A) antibodies protein motion and membrane fluidity were increased in normal membranes. This effect was observed also after spectrin depletion, which by itself increased protein motion but decreased membrane fluidity in the hydrophobic core of the membrane. The results show that membrane proteins influence the fluidity of membrane lipids.     

ESR研究急性运动及恢复期大鼠RBCM脂流动性的改变

本文以大鼠递增负荷力竭性运动为模型,利用电子自旋共振（ＥＳＲ）技术测定急性运动中及不同时程恢复期红细胞膜（ＲＢＣＭ）脂流动性的改变。ＲＢＣＭ脂尾部流动性在短时间中等强度运动（三级负荷末）即有明显下降（Ｐ＜０．０５）,在运动后恢复期进行性加重,并于运动后１２ｈ达极显著改变（Ｐ＜０．０１）：此时膜脂头部流动性也明显下降（Ｐ＜０．０５）。之后二者均有恢复趋势,提示递增负荷力竭性运动对ＲＢＣＭ脂流动性有重要影响,并且ＲＢＣＭ脂流动性与膜功能相互作用,互相影响     

The volume of extracellular fluid under conditions of long-term space flights

The volume of extracellular fluid (the bromine space) was determined in 18 cosmonauts 30 days before the start of a space flight and on the first day after landing. The duration of space flights on the Mir orbital station was from 126 to 438 days. Moreover, the volume of extracellular fluid was determined in seven cosmonauts directly during long-term space flights approximately two weeks before landing. After long-term space flights, the volume of extracellular fluid was decreased in all cosmonauts studied. The bromine space volume was significantly decreased compared to its initial preflight value. A decrease in the volume of extracellular fluid was caused not only by the reduction in the dense mass of the body but also by its dehydration. These processes developed independently of the duration of weightlessness but are mainly determined by the individual features of human beings.     

Influence of dietary cholesterol on polyunsaturated fatty acid composition, fluidity and membrane-bound enzymes in liver microsomes of rats fed olive and fish oil.

Male rats were fed diets containing olive or marine fish oils (10% w/w) with or without added cholesterol (1% w/w). After six weeks of feeding, the major fatty acid composition, fluidity, fatty acid desaturating and cholesterol biosynthesis/esterification related enzymes of liver microsomes were determined. Both olive oil and marine fish oil diets, without added cholesterol, enriched content of oleic and docosahexaenoic acids, respectively, of rat liver microsomes. The results were consistent with reduction in delta 6 and delta 5 desaturation of n-6 essential fatty acids and higher fluidity in the marine origin oil group. Inclusion of cholesterol into diets resulted in decreased membrane arachidonic acid content, with concomitant increase in linoleic acid content. Cholesterol feeding also decreased delta 6 and delta 5 desaturase activities, as well as membrane fluidity. Furthermore, the activity of acyl-CoA:cholesterol acyltransferase decreased, whereas the activity of hydroxymethylglutaryl-CoA reductase increased, in liver microsomes from both cholesterol-fat groups.     

Metabolic control of the membrane fluidity in Bacillus subtilis during cold adaptation

Membrane fluidity adaptation to the low growth temperature in Bacillus subtilis involves two distinct mechanisms: (1) long-term adaptation accomplished by increasing the ratio of anteiso- to iso-branched fatty acids and (2) rapid desaturation of fatty acid chains in existing phospholipids by induction of fatty acid desaturase after cold shock. In this work we studied the effect of medium composition on cold adaptation of membrane fluidity. Bacillus subtilis was cultivated at optimum (40 degrees C) and low (20 degrees C) temperatures in complex medium with glucose or in mineral medium with either glucose or glycerol. Cold adaptation was characterized by fatty acid analysis and by measuring the midpoint of phospholipid phase transition T(m) (differential scanning calorimetry) and membrane fluidity (DPH fluorescence polarization). Cells cultured and measured at 40 degrees C displayed the same membrane fluidity in all three media despite a markedly different fatty acid composition. The T(m) was surprisingly the highest in the case of a culture grown in complex medium. On the contrary, cultivation at 20 degrees C in the complex medium gave rise to the highest membrane fluidity with concomitant decrease of T(m) by 10.5 degrees C. In mineral media at 20 degrees C the corresponding changes of T(m) were almost negligible. After a temperature shift from 40 to 20 degrees C, the cultures from all three media displayed the same adaptive induction of fatty acid desaturase despite their different membrane fluidity values immediately after cold shock.     

水分胁迫对甘蔗叶片线粒体膜流动性的影响及其与膜脂过氧化的关系

用荧光探剂ANS对抗旱性不同的甘蔗品种在水分胁迫下叶片线粒体膜流动性的变化进行的研究表明,水分胁迫降低了线粒体膜的流动性,抗旱性强的甘蔗品种Co 617和F.Y.79-9的下降幅度分别小于抗旱性弱的Co 740和M.T.77-208;水分胁迫下线粒体膜流动性的下降与膜脂过氧化产物丙二醛含量的增加有密切关系。外源自由基处理试验也表明,甘蔗叶片线粒体膜流动性的下降与膜脂过氧化作用有关。     

In vivo phospholipid modification induces changes in microsomal delta 5-desaturase activity.

The phospholipid composition of rat-liver microsomes was modified by feeding weaning rats a choline-free diet. After 21 days, the phosphatidylcholine content decreased with a concomitant increment of phosphatidylserine and cholesterol. The bulk fluidity of the membrane decreased. Under these conditions, the delta 5-desaturase activity was diminished as well as the arachidonic-acid content of the membrane lipids.     

Effect of 8-alkylberberine homologues on erythrocyte membrane

8-alkylberberine homologues (Ber-C8-n, where n indicates carbon atom number of gaseous normal alkyl at 8 position, n = 0, 2, 4, 6, 8, 10, 12, or 16) were synthesized and their effects on the hemolysis of rabbit erythrocyte, the fluidity of membrane and the fluorescence of membrane protein were investigated by fluorescence analysis technique. Ber-C8-n with mediate length alkyl (4 < n < 10) exhibited obvious hemolysis effect on rabbit erythrocyte when their concentration exceed 1.25 x10(-4) mol/L, and Ber-C8-8 displayed the highest hemolysis effect among all tested homologues. All of Ber-C8-n influenced the fluidity of erythrocyte membrane to different extents, which exhibited an obvious dose-effect relationship. The effect of Ber-C8-n on fluidity increased as the length of alkyl chain was elongated and decreased gradually when the alkyl carbon atoms exceeded 8. The fluorescence of erythrocyte membrane protein was quenched by Ber-C8-n, which showed a similar changing tendency on membrane fluidity. Experiments in vitro suggested that disturbing effects of Ber-C8-n on the conformation and function of membrane protein leaded to the changes of membrane fluidity and stability, and then the membrane was broken down.     

Optimisation of plant sterols incorporation in human keratinocyte plasma membrane and modulation of membrane fluidity.

The in vitro effects of plant sterols were investigated with regard to their uptake and membrane lipid fluidity in human keratinocytes. Among the different media tested to transport sterols (liposomes, micelles and organic solvents), the best results in terms of incorporation and viability were obtained by the use of the organic solvents dimethylsulfoxide and ethanol. After 48 h incubation exogenous sterol can account for about 30% of the total cell sterol content. The total sterol amount in plasma membranes increased 2-fold after incubation with cholesterol, whereas it was not altered when phytosterols were incorporated. The incorporation of cholesterol, sitosterol and stigmasterol led to an increase in the percent of unsaturated fatty acid C18:1 in the plasma membrane. The effect of this uptake on membrane fluidity was studied by means of fluorescence polarisation using DPH and TMA-DPH as fluorescent probes. Whereas cholesterol and sitosterol had no significant effect on the DPH fluorescence anisotropy (rs), the presence of stigmasterol induced a 12% decrease of rs reflecting an increase in membrane fluidity. We can conclude from this study that in the presence of sitosterol, the mean fluidity of the membrane is regulated whereas stigmasterol triggers a looseness of molecular packing of phospholipids acyl chains, in accordance with previous results obtained on purely lipid model membranes.     

Effects of r—HuEPO on the biophysical characteristics of erythrocyte membrane in patients with anemia of chronic renal failure

Using electron spin resonance (ESR) spin labeling technique,we have studied the conformation of sulfhydryl groups(-SH) binding sites in membrane proteins and mem brane fluidity of red blood cells(RBCs) from two groups of patients with anemia of chronic renal failure(ACRF).One of the groups is composed of patients who were untreated with recombinant human erythropoietin(r-HuEPO),and the other is composed of patients who were treated with r-HuEPO.The results indicated:1)the conformation of SH group binding site in RBC membrane proteins from former group was different from those of healty people.2)the fluidity in the region near the surface of RBC membrane from former group was lower than those of healthy people.3)However,the above biophysical properties of RBC membrane from later group were normal.We concluded that RBC membrane in patients with ACRF was abnormal,and the treatment of r-HuEPO may promote the production of normal RBCs,thus ameliorate the biophysical properties of RBCs from the patients with ACRF.     

Estimation of cell membrane properties and erythrocyte red-ox balance in patients with metabolic syndrome

Metabolic syndrome (MS) is associated with occurrence of the many cardiovascular risk factors such as atherogenic dyslipidemia, visceral fat distribution, arterial hypertension and pro-thrombotic and pro-inflammatory status. In our study the effect of disorders that appear in MS on red-ox balance and erythrocyte cell membrane properties were estimated. The study comprised 50 patients with diagnosed MS and in 25 healthy subjects. Content of thiobarbituric acid reactive substances (TBARS) and catalase, superoxide dismutase and glutathione peroxidase activity were estimated in red blood cells. Moreover, conformation status of membrane proteins, membrane fluidity and osmotic fragility were evaluated. MS was found to manifest: (1) the increase of the concentration of TBARS in erythrocytes with no statistically significant differences in antioxidant enzymes activity, (2) disorders in the structure of erythrocyte cytoskeleton proteins, (3) the increase in membrane lipids fluidity at the depth of 5th and 12th carbon atom of fatty acid hydrocarbon chain and significantly decreased fluidity at the depth of 16th carbon atom, (4) increased erythrocyte osmotic fragility.     

Cardiorespiratory responses to physical work during and following 17 days of bed rest and spaceflight.

To determine the influence of a 17-day exposure to real and simulated spaceflight (SF) on cardiorespiratory function during exercise, four male crewmembers of the STS-78 space shuttle flight and eight male volunteers were studied before, during, and after the 17-day mission and 17 days of -6 degrees head-down-tilt bed rest (BR), respectively. Measurements of oxygen uptake, pulmonary ventilation, and heart rate were made during submaximal cycling 60, 30, and 15 days before the SF liftoff and 12 and 7 days before BR; on SF days 2, 8, and 13 and on BR days 2, 8, and 13; and on days 1, 4, 5, and 8 after return to Earth and on days 3 and 7 after BR. During 15 days before liftoff, day 4 after return, and day 8 after return and all BR testing, each subject completed a continuous exercise test to volitional exhaustion on a semirecumbent (SF) or supine (BR) cycle ergometer to determine the submaximal and maximal cardiorespiratory responses to exercise. The remaining days of the SF testing were limited to a workload corresponding to 85% of the peak pre-SF peak oxygen uptake (Vo2 peak) workload. Exposure to and recovery from SF and BR induced similar responses to submaximal exercise at 150 W. Vo2 peak decreased by 10.4% from pre-SF (15 days before liftoff) to day 4 after return and 6.6% from pre-BR to day 3 after return, which was partially (SF: -5.2%) or fully (BR) restored within 1 wk of recovery. Workload corresponding to 85% of the peak pre-SF Vo2 peak showed a rapid and continued decline throughout the flight (SF day 2, -6.2%; SF day 8, -9.0%), reaching a nadir of -11.3% during testing on SF day 13. During BR, Vo2 peak also showed a decline from pre-BR (BR day 2, -7.3%; BR day 8, -7.1%; BR day 13, -9.0%). These results suggest that the onset of and recovery from real and simulated microgravity-induced cardiorespiratory deconditioning is relatively rapid, and head-down-tilt BR appears to be an appropriate model of this effect, both during and after SF.     

Differences in composition and fluidity of intestinal microvillus membrane vesicles prepared by different methods

Multiple methods have been developed to isolate the intestinal microvillus membrane and facilitate the study of its composition and function. Variations in membrane composition and fluidity may result from different preparative techniques. This study shows that the use of MgCl2 and/or KSCN in vesicle preparation alters phospholipid and protein composition of the membrane compared to CaCl2 precipitation. The use of MgCl2 in membrane preparation increased phosphatidylethanolamine and decreased phosphatidylinositol content. The use of KSCN in membrane preparation decreased the protein content. The structural changes seen with the use MgCl2 alone are accompanied by an increase in both static and dynamic membrane fluidity. These results suggest that different methods of membrane vesicle preparation affect membrane phospholipid and protein content as well as membrane fluidity.     

Effects of rectification on synaptic efficacy.

We have investigated the effects of postsynaptic membrane properties on the shape of synaptic potentials generated by time-varying synaptic conductances. We used numerical simulation techniques to model cells of several different geometrical forms, from an isopotential sphere to a neuron with a soma and a dendritic tree. A variety of postsynaptic membrane properties were tested: (a) a passive resistance-capacitance membrane, (b) a membrane represented by the Hodgkin and Huxley (HH) equations, and (c) a membrane that was passive except for a delayed rectification represented by a voltage- and time-dependent increase in GK. In all cases we investigated the effects of these postsynaptic membrane properties on synaptic potentials produced by synaptic conductances that were fast or slow compared with the membrane time constant. In all cases the effects of postsynaptic rectification occurred on postsynaptic potentials of amplitudes as low as 1 mV. The HH model (compared with the passive model) produced an increased peak amplitude (from the increase in GNa) but a decreased half-width and a decreased time integral (from the increase in GK). These effects of the HH GK change were duplicated by a simple analytical rectifier model.