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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Fracture Description of the HFTS-2 Slant Core, Delaware Basin, West Texas

Previous work in the Midland Basin Hydraulic Fracture Test Site project (HFTS1) has shown the value of core recovered from a stimulated volume in providing information on the geometry and extent of hydraulic fractures. This project (HFTS2) is in the Wolfcamp Formation of the Delaware Basin. A slant core through the stimulated volume was acquired above and below a stimulated well and the results of the fracture description are presented here. Here, nine, 3-inch-diameter whole cores from the slant well were examined for fractures prior to slabbing, together with a CT scan of the core. We used criteria developed during the HFTS1 project to identify hydraulic, natural, drilling-induced and core-handling fractures. Material collected from a few fracture faces was cleaned, sieved, and examined under a microscope to look for proppant. A total of 1261 fractures, including 500 hydraulic fractures, were described in 948 feet of core. Hydraulic fractures are not evenly distributed through the cores; they tend to occur in clusters. Many are remarkably planar, smooth, and featureless, while others have twist hackles, steps, plumose, and kinks. Natural, subvertical fractures, mostly less than 1 mm in width, sealed with blocky calcite, are oriented NE-SW (Set 1) and WNW-ESE (Set 2). Two Set 1 fractures have drusy cement on parted faces and were possibly open prior to drilling. A few subvertical sealed fractures with different orientations are also present. Bed-parallel natural fractures, most having fibrous cement (beef), and some showing top-to-north bed-parallel shear are present. Faults with normal/oblique movement were found in one part of the core. Drilling induced and core-handling breaks were identified in all cores, and were also noted to have reactivated some natural fractures. The results from this work will allow hydraulic fracture distribution relative to the stimulated well to be assessed. The number of fractures is generally greater than the number of perforations, but these can be compared for different stages and perforation clusters. Surface features provide information about the direction of hydraulic fracture propagation and about segmentation and bifurcation that might increase the number of fracture strands. Reactivation of natural fractures, including bedding-parallel fractures, occurs although the mechanism of parting is mostly unknown. The wider HFTS2 project will make use of this fracture description to improve hydraulic fracture modeling (geomechanics and engineering), to help explain pressure depletion and fiber optics observations (reservoir depletion and frac geometry), to help verify indirect fracture diagnostic techniques such as microseismic monitoring (geophysics), and to help calibrate horizontal well image logs.

58 GEOSCIENCES↗
DOE OSTI2021

A Systematic Interpretation of Subsurface Proppant Concentration from Drilling Mud Returns: Case Study from Hydraulic Fracturing Test Site (HFTS-2) in Delaware Basin

The aim of this study is generation and validation of a proppant log using analysis of drilling mud returns for child wells. Proppant log provides qualitative as well as quantitative insights into spatial distribution of proppant sand particles from prior stimulation of parent wells. While the basic methodology was developed and formalized during analysis of material collected from through fracture cores at Hydraulic Fracturing Test Site in Midland Basin (HFTS – 1), the test wells at HFTS – 2 in the neighboring Delaware Basin allowed the opportunity to validate the workflow on actual mud return samples from subsurface. As a child well is being drilled, periodic mud return samples are collected at the rig site and preserved for analysis. The workflow involves systematic cleaning of the samples including various steps such as washing, drying and segregation of samples into relevant size fractions of interest (< Mesh 20) based on specifications of pumped sand during stimulation of the parent well. Clean samples are imaged using high resolution transparency scanning. Scan images are then systematically analyzed for particles of interest using computer vision techniques. Sample counts are further validated using elemental analysis of smaller sub-samples at various depths of interest. This step is necessary to isolate proppant versus other naturally occurring minerals such as sulphates and carbonates which show similar optical properties. We successfully correlated proppant distribution against the existing parent well and validated propped versus relatively un-propped zones for a child well at the test site. The advantage of testing the proppant log concept at the HFTS – 2 site is the plethora of additional diagnostic data that is available to validate our primary observations. We can correlate spatial proppant distribution against variability in stimulation response based on independent observations such as image logs, microseismic attributes as well as DAS response, all of which tend to corroborate one another. One of our significant successes was being able to describe varying degrees of impact of the parent well along the lateral length of a stimulated child well. Our workflow represents a systematic and one-of-a-kind interpretation of spatial proppant distribution while drilling child wells. This provides unique opportunities to better understand the current state of the Downloaded from http://onepetro.org/URTECONF/proceedings-pdf/21URTC/2-21URTC/D021S031R003/2477415/urtec-2021-5189-ms.pdf/1 by Carol Worster on 28 February 2022 URTeC 5189 2 reservoir being targeted including zones which are likely more drained relative to others and how the planned completion of the child well can be improved. Lastly, this log can be useful is validating optimal well spacing in relatively new fields under development.

58 GEOSCIENCES↗
DOE OSTI2021

Subsurface Characterization of Hydraulic Fracture Test Site-2 (HFTS-2), Delaware Basin

Hydraulic Fracturing Test Site-2 (HFTS-2) is a field-based research experiment performed in the Wolfcamp Formation of the Permian (Delaware) Basin. This paper focuses on integration, advanced geological characterization, and 3D subsurface modeling of the comprehensive HFTS-2 dataset. The study showcases a multidisciplinary reservoir characterization approach that incorporates geology, petrophysics, geochemistry, geomechanics, microseismic, and subsurface engineering analysis. Subsurface characterization of organic-rich mudstone formations requires understanding complex hydraulic fracture network growth in relation to inherent lithology, geomechanical properties, and interaction with pre-existing natural fractures. This paper presents a characterization workflow incorporating pre- and post-stimulation subsurface data, unique to the HFTS-2 dataset. The study integrated: (1) rock properties from logs, cores, and thin sections; (2) natural and hydraulic fracture descriptions from cores and image logs; (3) local and regional stresses; (4) geomechanics; (5) microseismic; (6) fiber optic (FO) and bottomhole pressure gauge (BHPG) response; and (7) produced fluids analysis. During a stimulation treatment, creation of the stimulated rock volume (SRV) is influenced by several subsurface factors. Key contributing factors include structural context, stress conditions, lithology, facies architecture, pre-existing natural fractures, and geomechanical properties. The HFTS-2 subsurface data integration indicates that the SRV is comprised of a complex juxtaposition of hydraulic fracture swarms, as evidenced by image logs analysis, core description, and microseismic monitoring. The HFTS-2 microseismic event density was used to generate 3D heat maps that serve as a representative SRV footprint, corroborated by secondary datasets. These maps were further integrated with petrophysical and geomechanical characteristics, as well as responses from FO and BHPG, to estimate the lateral and vertical dimensions of the effective fractures. The geological characterization for the HFTS-2 dataset combined with 3D modeling for petrophysical and geomechanical properties provides a strong foundation for subsurface simulation and optimization studies. Downloaded from http://onepetro.org/URTECONF/proceedings-pdf/21URTC/1-21URTC/D011S005R001/2477501/urtec-2021-5243-ms.pdf/1 by Carol Worster on 28 February 2022 URTeC 5243 The workflow improved our understanding of HFTS-2 hydraulic fracture propagation and characteristics in relation to offset pressure depletion and interaction with pre-existing natural fractures. Analysis showed that fracture geometry varies by stage and by well, and a complex fracture network is generated with varying fracture density. The multidisciplinary workflow presented herein for integration and characterization serves as a foundation to evaluate completion efficiency and estimate areal and vertical stimulation and depletion extent for the project. Furthermore, the workflow and learnings can also be transferred to other unconventional plays.

58 GEOSCIENCES↗
DOE OSTI2024

Connecting Nitrogen Transformations Mediated by the Rhizosphere Microbiome to Perennial Cropping System Productivity in Marginal Lands

The demand for energy from biofuel production is increasing, prompting concerns about the environmental impact and long-term sustainability of bioenergy cropping systems. These cropping systems will make up much of our future landscapes, and threaten to take the place of food cropping systems. Many life cycle analyses of bioenergy sustainability focus on carbon accrual and budgets, since they want to maximize carbon accrual while producing alternative fuel. Less attention has been given to nitrogen (N) dynamics in these systems. N is the most commonly limiting nutrient for plants, but applying nitrogen fertilizer- as we do for most cropping systems – is harmful to the environment, energetically costly, and produces greenhouse gases. In other words, adding nitrogen by fertilizer bioenergy systems could add to the very problems (climate change) it is trying to address. This is especially true for the areas that are proposed for bioenergy systems: marginal lands. These more degraded lands do not complete with food crops, but do have limited nitrogen. If we are to use these marginal lands for bioenergy, we need to understand the mechanisms regulating nutrient acquisition, and identify ways that bioenergy crops can get nitrogen in sustainable ways. Nutrient acquisition in the soil is performed by microbes in the root zone, or rhizosphere. Microbes can either mineralize nitrogen in the soil (from organic forms) or fix nitrogen from the air, in a process called nitrogen fixation. The goal of our project was thus to understand how the rhizosphere microbiome provides nutrients to bioenergy crops on marginal lands. We focus especially on the process of nitrogen fixation, since it has potential to get “fertilizer for free” that has much less environmental harm. We investigated this goal using sites from the DOE Great Lakes Bioenergy Research Center (GLBRC) in the upper Midwest, and associated lab and ‘omics methods. We group our findings into three major areas. First, we showed that nitrogen fixation, the conversion of N2 gas from the air to ammonium that is usable by plants, is performed in bioenergy soils, and benefits switchgrass crops. While more well-studied in leguminous plants, free-living nitrogen fixation can occur in some systems, and represents a potential opportunity to gain ‘free’ sustainable nitrogen source. We identified the nitrogen fixing bacteria that were most active in providing switchgrass with N, and showed that the drivers of nitrogen fixation occurred at a microscale; it is not well-predicted by bulk variables like soil moisture or plant phenology. Second, we showed that nitrogen fixation is not suppressed by long-term fertilizer. We expected that plentiful nitrogen would reduce the symbiotic relationship between nitrogen fixers and plants, and ‘downregulate’ fixation. We did not find evidence for this, either after long-term fertilizer in the field, or short-term fertilizer in the greenhouse. Finally, we identified the root exudates, carbon compounds that are emitted from the root, that best stimulate nitrogen fixation. We found that carbohydrates were better at stimulating fixation than organic acids. We expected these exudates to be emitted from the plant in periods of high N demand, but we found they are emitted when N is plentiful. This suggests that the stimulation of N fixation by plants is a passive process. Overall, we show that nitrogen fixation has potential to support bioenergy cropping system, and future management could develop ways to maximize it. However, this may not be best achieved via the plant – we found very little evidence of a ‘transactional’ system by which plants are controlling when and where nitrogen fixation is stimulated. It will be better to understand how management practices like planting and fertilizer application affect the microscale soil dynamics, which will determine nitrogen fixation rates.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1990

Stretch-induced prostaglandins and protein turnover in cultured skeletal muscle

The purpose of the study is to determine whether mechanical stimulation of cultured muscle cells influences prostaglandin efflux rates and whether they are related to stretch-induced alterations in protein turnover rates. The materials and methods of the experiment, including cell cultures, mechanical stimulation, protein synthesis, and degradation assays are outlined, and emphasis is placed on the effect of short-term mechanical stimulation in basal medium prostaglandin efflux from cultured skeletal muscle and stretch-induced alterations in prostaglandins efflux in complete medium. The major finding of the study is that mechanical stimulation of tissue-cultured skeletal-muscle cells under conditions inducing skeletal-muscle hypertropy increases the efflux of PGE(2) and PGE(2-alpha) but not 6-keto-PGF(1-alpha), the prostacyclin product.

Vandenburgh, Herman H.↗
NASA NTRS1982

Susceptibility of the squirrel monkey to different motion conditions

The exact stimulus eliciting vomiting in animal studies of motion sickness is difficult to specify because the vestibular stimulation produced by many motion conditions is confounded by voluntary movements with animals. This is an important problem because experiments with animal models of motion sickness can provide useful information about antimotion sickness drugs or the role of neural mechanisms, only when animals are exposed to the same motion stimuli in each experimental session. A series of tests were conducted to determine the susceptibility of 15 adult squirrel monkeys to motion sickness in freely moving and restrained test conditions. Canal stimulation was varied by exposing the monkey in freely moving conditions to varying degrees of angular velocity (60, 90, 120, 150 deg/sec), and in restrained conditions to one angular velocity (150 deg/sec) and to cross-coupling effects of whole-body roll movements during rotation. Otolith stimulation was investigated by using sinusoidal vertical linear acceleration during free movement conditions, and off-vertical rotation and earth-horizontal (BBQ) rotation while restrained. The percentage of freely moving animal vomiting during vertical axis rotation was 27, 93, 86, and 92 for the angular velocities of 60, 90, 120, and 150 deg/sec respectively. None of the monkeys vomited during vertical axis rotation or cross-coupled rotation when restrained. Otolith stimulation appears to be a less provocative stimulus for the squirrel monkey as the percentage of animals vomiting were 13, 0, and 7 for the conditions of free movement during oscillation, restraint during off-vertical, and BBQ rotation respectively. Motion sickness to the point of vomiting occurred regularly only in conditions where self-motion was possible. Such effects could occur because voluntary movement during motion augments vestibular effects by producing self-inflicted cross-coupling, but the failure to elicit vomiting with experimenter-coupling cross-coupling argues against this interpretation. Alternatively, these results might imply that feedback from movement control mechanisms may play an important role in sensory conflict as suggested by Oman's sensory-motor conflict theory.

R A Fox↗
NASA NTRS1994

Early alterations in soleus GLUT-4, glucose transport, and glycogen in voluntary running rats

Voluntary wheel running (WR) by juvenile female rats was used as a noninterventional model of soleus muscle functional overload to study the regulation of insulin-stimulated glucose transport activity by the glucose transporter (GLUT-4 isoform) protein level and glycogen concentration. Soleus total protein content was significantly greater (+18%;P greater than 0.05) than in age-matched controls after 1 wk of WR, and this hypertrophic response continued in weeks 2-4 (+24-32%). GLUT-4 protein was 39% greater than in controls in 1-wk WR soleus, and this adaptation was accompanied by a similar increase in in vitro insulin-stimulated glucose transport activity(+29%). After 2 and 4 wk of WR, however, insulin-stimulated glucose transport activity had returned to control levels, despite a continued elevation (+25-28%) of GLUT-4 protein. At these two time points, glycogen concentration was significantly enhanced in WR soleus (+21-42%), which coincided with significant reductions in glycogen synthase activity ratios (-23 to-41%). These results indicate that, in this model of soleus muscle functional overload, the GLUT-4 protein level may initially regulate insulin-stimulated glucose transport activity in the absence of changes in other modifying factors. However,this regulation of glucose transport activity by GLUT-4 protein may be subsequently overridden by elevated glycogen concentration.

Henriksen, Erik J.↗
NASA NTRS1995

Spectroscopic Investigation of Ce(3+) Doped Fluoride Crystals

Doping of the trivalent rare-earth cerium ion into fluoride crystals is of interest in producing turnable ultra-violet solid state lasers. These lasers are desirable for many applications in medicine, industry, and scientific research, including remote sensing. High absorption and stimulated emission cross sections of the dipole allowed 4f-5d transitions show promise in cerium as a laser ion in crystals. Several research groups have already reported the observation of stimulated emission of cerium in LiYF4, LiSrAlF6, and LiCaAlF6. However, the color center formation in the crystals due to the excited state absorption of ultra-violet pump light adds difficulty to achieving laser action. We have investigated the spectroscopic properties of cerium such as absorption and emission spectra, and lifetimes in four different fluoride crystals, including LiCaAlF6, LiSrAlF6, KyF4 and LiYF4. We have derived the polarized absorption and stimulated emission cross sections from transmission and fluorescence emission measurements for each of the host crystals. we have measured the lifetime of the lowest 5d level; moreover, investigated the temperature dependence of this lifetime and color center formation. Our results on absorption and stimulated emission cross sections for LiCaAlF6 and LiSrAlF6 are similar to the results already published.

Reinhart, Donald H.↗
NASA NTRS1992

Fatigability and Blood Flow in the Rat Gastrocnemius-Plantaris-Soleus after Hindlimb Suspension

The purpose of this study was to test the hypothesis that hindlimb suspension increases the fatigability of the soleus during intense contractile activity and determine whether the increased fatigue is associated with a reduced muscle blood flow. Cage-control (C) and 15-day hindlimb-suspended (HS) rats were anesthetized, and either the gastrocnemius-plantaris-soleus (G-P-S) muscle group or the soleus was stimulated (100 Hz, 100-ms trains at 120/min) for 10 min in situ. In the G-P-S preparation, blood flow was measured with radiolabeled microspheres before and at 2 and 10 min of contractile activity. The G-P-S fatigued markedly at this stimulation frequency, and the differences between C and HS animals were not significant until the 9th min of contractile activity. In contrast, the stimulation resulted in faster rates and significantly larger amounts of fatigue in the soleus from HS than from C animals. The atrophied soleus showed significant differences by I min of stimulation (C = 70 +/- 1% vs. HS = 57 +/- 2% of peak train force) and remained different at 10 min (C = 64 +/- 4% vs. HS = 45 +/- 2% peak train force). Relative blood flow to the soleus was similar between groups before and during contractile activity (rest: C = 20 +/- 3 vs. HS= 12 +/- 3; 2 min: C= 128 +/- 6 vs. HS = 118 +/- 4; 10 min: C = 123 +/- 11 vs. HS = 105 +/- 11 ml min(exp -1) 100 g(exp -1)). In conclusion, these results established that 15 days of HS increased the fatigability of the soleus, but the effect was not caused by a reduced muscle blood flow.

McDonald, K. S.↗
NASA NTRS2000

Centrifugation of Cultured Osteoblasts And Macrophages as a Model To Study How Gravity Regulates The Function of Skeletal Cells

Mechanical loading helps define the architecture of weight-bearing bone via the tightly regulated process of skeletal turnover. Turnover occurs by the concerted activity of osteoblasts, responsible for bone formation. and osteoclasts, responsible for bone resorption. Osteoclasts are specialized megakaryon macrophages, which differentiate from monocytes in response to resorption stimuli, such as reduced weight-bearing. Habitation in space dramatically alters musculoskeletal loading, which modulates both cell function and bone structure. Our long-term objective is to define the molecular and cellular mechanisms that mediate skeletal adaptations to altered gravity environments. Our experimental approach is to apply hypergravity loads by centrifugation to rodents and cultured cells. As a first step, we examined the influence of centrifugation on the structure of cancellous bone in rats to test the ability of hypergravity to change skeletal architecture. Since cancellous bone undergoes rapid turnover we expected the most dramatic structural changes to occur in the shape of trabeculae of weight-bearing, cancellous bone. To define the cellular responses to hypergravity loads, we exposed cultured osteoblasts and macrophages to centrifugation. The intraosseous and intramedullary pressures within long bones in vivo reportedly range from 12-40 mm Hg, which would correspond to 18-59 gravity (g) in our cultures. We assumed that hydrostatic pressure from the medium above the cell layer is at least one major component of the mechanical load generated by centrifuging cultured cells. and therefore we exposed the cells to 10-50g. In osteoblasts, we examined the structure of their actin and microtubule networks, production of prostaglandin E2 (PGE2), and cell survival. Analysis of the shape of the cytoskeletal networks provides evidence for the ability of centrifugation to affect cell structure, while the production of PGE2 serves as a convenient marker for mechanical stimulation. We examined cell survival, reasoning that osteoblasts might mold skeletal structure in a hypergravity environment in part by regulating apoptosis and thus the duration of osteoblast productivity. Finally, we tested the influence of centrifugation on microbial activation of a macrophage cell line (RAW264.7). In response to the appropriate hormonal stimulation, this cell line is reportedly capable of undergoing differentiation to express osteoclast markers. In addition, a component of the cell wall of gram-negative bacteria, lipopolysaccaride (LPS), stimulates the formation of osteoclasts in vivo. Thus we tested the influence on centrifugation on RAW264.7 cells stimulated with LPS to provide an index of the function of osteoclast precursors.

Globus, Ruth K.↗
NASA NTRS2002

Effect of Serum from Chickens Treated with Clenbuterol on Myosin Accumulation, Beta-Adrenergic Receptor Population, and Cyclic AMP Synthesis in Embryonic Chicken Skeletal Muscle Cell Cultures

Broiler chickens at 35 d of age were fed 1 ppm clenbuterol for 14 d. This level of dietary clenbuterol led to 5-7% increases in the weights of leg and breast muscle tissue. At the end of the 14-d period, serum was prepared from both control and clenbuterol-treated chickens, and was then employed as a component of cell culture media at a final concentration of 20% (v/v). Muscle cell cultures were prepared from both the leg and the breast muscle groups of 12-d chick embryos. Treatment groups included control chicken serum to which 10 nM, 50 nM, and 1 uM clenbuterol had been added, as well as cells grown in media containing 10% horse serum. Cultures were subjected to each treatment for 3 d, beginning on the seventh d in culture. Neither the percent fusion nor the number of nuclei in myotubes was significantly affected by any of the treatments. The quantity of myosin heavy chains (MHCs) was not increased by serum from clenbuterol-treated chickens in either breast or leg muscle cultures; however, the MHC quantity was 50-150% higher in cultures grown in control chicken serum to which 10 and 50 nM clenbuterol had also been added. The B-adrenergic receptor (betaAR) population was 4000-7000 betaARs per cell in cultures grown in chicken serum with leg muscle cultures having approximately 25-30% more receptors than breast muscle Culture. Receptor population was not significantly affected by the presence of clenbuterol or by the presence of serum from clenbuterol-treated chickens. In contrast, the betaAR Population in leg and breast muscle cultures grown in the presence of 10% horse serum was 16,000-18,000 betaARs per cell. Basal concentration of cyclic adenosine 3':5'monophosphate (cAMP) was not significantly affected by the treatments. When cultures grown in chicken serum were stimulated for 10 min with 1 uM isoproterenol, limited increases of 12-20% in cAMP Concentration above the. basal levels were observed. However, when cultures grown in the presence of horse serum were stimulated with 1 uM isoproterenol, cAMP concentration was stimulated 5- to 9-fold above the basal levels. Thus, not only did cells, grown in horse serum have a higher PAR population, but also each receptor had a higher capacity for cAMP synthesis following isoproterenol stimulation. Finally, the hypothesis that clenbuterol exerts its action on muscle protein content by changes in cAMP concentration was tested. No correlation was apparent between basal cAMP concentration and MHC content.

Young, Ronald B.↗
NASA NTRS2003

TNF-alpha increases ubiquitin-conjugating activity in skeletal muscle by up-regulating UbcH2/E220k

In some inflammatory diseases, TNF-alpha is thought to stimulate muscle catabolism via an NF-kappaB-dependent process that increases ubiquitin conjugation to muscle proteins. The transcriptional mechanism of this response has not been determined. Here we studied the potential role of UbcH2, a ubiquitin carrier protein and homologue of murine E220k. We find that UbcH2 is constitutively expressed by human skeletal and cardiac muscles, murine limb muscle, and cultured myotubes. TNF-alpha stimulates UbcH2 expression in mouse limb muscles in vivo and in cultured myotubes. The UbcH2 promoter region contains a functional NF-kappaB binding site; NF-kappaB binding to this sequence is increased by TNF-alpha stimulation. A dominant negative inhibitor of NF-kappaB activation blocks both UbcH2 up-regulation and the increase in ubiquitin-conjugating activity stimulated by TNF-alpha. In extracts from TNF-alpha-treated myotubes, ubiquitin-conjugating activity is limited by UbcH2 availability; activity is inhibited by an antiserum to UbcH2 or a dominant negative mutant of UbcH2 and is enhanced by wild-type UbcH2. Thus, UbcH2 up-regulation is a novel response to TNF-alpha/NF-kappaB signaling in skeletal muscle that appears to be essential for the increased ubiquitin conjugation induced by this cytokine.

Non-NASA Center↗
NASA NTRS2002

Do vestibular otolith organs participate in human orthostatic blood pressure control?

We hypothesized that vestibular otolith organ stimulation contributes to human orthostatic responses. Twelve subjects underwent three 60 degrees upright tilts: (1) with the neck flexed from 0 degrees to 30 degrees relative to the body during 60 degrees tilt, such that the head moved from horizontal to 90 degrees above horizontal (0 to 1 Gz otolith stimulation); (2) with the head and body aligned, such that they tilted together to 60 degrees (0 to 0.87 Gz otolith stimulation); and (3) with the neck flexed 30 degrees relative to the body during supine conditions, and the neck then extended to -30 degrees during 60 degrees body tilting, such that the head remained at 30 degrees above horizontal throughout body tilting (constant 0.5 Gz otolith stimulation). All three tilt procedures increased thoracic impedance, sympathetic nerve activity (N = 8 of 12), arterial pressure, and heart rate relative to supine conditions (all P < 0.04). Within the first 20 s of tilt, arterial pressure increased most obviously in the 0 to 1 Gz otolith condition. Thoracic impedance tended to increase more in otolith-constant conditions, but no dependent variable differed significantly between tilt conditions, and no significant time x tilt interactions emerged. Otolith inputs may contribute to early transient adjustments to orthostasis. However, lack of significant main effects of tilt condition and time x tilt interactions suggests that potential otolith effects on the variables we studied are relatively subtle and ephemeral, or that other mechanisms compensate for a lack of change in otolith input with orthostasis.

Non-NASA Center↗
NASA NTRS2001

The anabolic activity of bone tissue, suppressed by disuse, is normalized by brief exposure to extremely low-magnitude mechanical stimuli

It is generally believed that mechanical signals must be large in order to be anabolic to bone tissue. Recent evidence indicates, however, that extremely low-magnitude (<10 microstrain) mechanical signals readily stimulate bone formation if induced at a high frequency. We examined the ability of extremely low-magnitude, high-frequency mechanical signals to restore anabolic bone cell activity inhibited by disuse. Adult female rats were randomly assigned to six groups: baseline control, age-matched control, mechanically stimulated for 10 min/day, disuse (hind limb suspension), disuse interrupted by 10 min/day of weight bearing, and disuse interrupted by 10 min/day of mechanical stimulation. After a 28 day protocol, bone formation rates (BFR) in the proximal tibia of mechanically stimulated rats increased compared with age-matched control (+97%). Disuse alone reduced BFR (-92%), a suppression only slightly curbed when disuse was interrupted by 10 min of weight bearing (-61%). In contrast, disuse interrupted by 10 min per day of low-level mechanical intervention normalized BFR to values seen in age-matched controls. This work indicates that this noninvasive, extremely low-level stimulus may provide an effective biomechanical intervention for the bone loss that plagues long-term space flight, bed rest, or immobilization caused by paralysis.

Non-NASA Center↗
NASA NTRS1986

Characterization of nucleoside triphosphatase activity in isolated pea nuclei and its photoreversible regulation by light

A nucleoside triphosphatase (NTPase) present in highly purified preparations of pea nuclei was partially characterized. The activity of this enzyme was stimulated by divalent cations (Mg2+ = Mn2+ > Ca2+), but was not affected by the monovalent cations, Na+ and K+. The Mg(2+)-dependent activity was further stimulated by concentrations of Ca2+ in the low micromolar range. It could catalyze the hydrolysis of ATP, GTP, UTP, and CTP, all with a pH optimum of 7.5. The nuclear NTPase activity was not inhibited by vanadate, oligomycin, or nitrate, but was inhibited by relatively low concentrations of quercetin and the calmodulin inhibitor, compound 48/80. The NTPase was stimulated more than 50% by red light, and this effect was reversed by subsequent irradiation with far-red light. The photoreversibility of the stimulation indicated that the photoreceptor for this response was phytochrome, an important regulator of photomorphogenesis and gene expression in plants.

NASA Discipline Plant Biology↗
NASA NTRS2000

Integrin activation and focal complex formation in cardiac hypertrophy

Cardiac hypertrophy is characterized by both remodeling of the extracellular matrix (ECM) and hypertrophic growth of the cardiocytes. Here we show increased expression and cytoskeletal association of the ECM proteins fibronectin and vitronectin in pressure-overloaded feline myocardium. These changes are accompanied by cytoskeletal binding and phosphorylation of focal adhesion kinase (FAK) at Tyr-397 and Tyr-925, c-Src at Tyr-416, recruitment of the adapter proteins p130(Cas), Shc, and Nck, and activation of the extracellular-regulated kinases ERK1/2. A synthetic peptide containing the Arg-Gly-Asp (RGD) motif of fibronectin and vitronectin was used to stimulate adult feline cardiomyocytes cultured on laminin or within a type-I collagen matrix. Whereas cardiocytes under both conditions showed RGD-stimulated ERK1/2 activation, only collagen-embedded cells exhibited cytoskeletal assembly of FAK, c-Src, Nck, and Shc. In RGD-stimulated collagen-embedded cells, FAK was phosphorylated only at Tyr-397 and c-Src association occurred without Tyr-416 phosphorylation and p130(Cas) association. Therefore, c-Src activation is not required for its cytoskeletal binding but may be important for additional phosphorylation of FAK. Overall, our study suggests that multiple signaling pathways originate in pressure-overloaded heart following integrin engagement with ECM proteins, including focal complex formation and ERK1/2 activation, and many of these pathways can be activated in cardiomyocytes via RGD-stimulated integrin activation.

NASA Discipline Cardiopulmonary↗
NASA NTRS2000

Fibroblast growth factor-2 promotes keratan sulfate proteoglycan expression by keratocytes in vitro

Keratocytes of the corneal stroma produce a specialized extracellular matrix responsible for corneal transparency. Corneal keratan sulfate proteoglycans (KSPG) are unique products of keratocytes that are down-regulated in corneal wounds and in vitro. This study used cultures of primary bovine keratocytes to define factors affecting KSPG expression in vitro. KSPG metabolically labeled with [(35)S]sulfate decreased during the initial 2-4 days of culture in quiescent cultures with low serum concentrations (0.1%). Addition of fetal bovine serum, fibroblast growth factor-2 (FGF-2), transforming growth factor beta, or platelet derived growth factor all stimulated cell division, but only FGF-2 stimulated KSPG secretion. Combined with serum, FGF-2 also prevented serum-induced KSPG down-regulation. KSPG secretion was lost during serial subculture with or without FGF-2. Expression of KSPG core proteins (lumican, mimecan, and keratocan) was stimulated by FGF-2, and steady state mRNA pools for these proteins, particularly keratocan, were significantly increased by FGF-2 treatment. KSPG expression therefore is supported by exogenous FGF-2 and eliminated by subculture of the cells in presence of serum. FGF-2 stimulates KSPG core protein expression primarily through an increase in mRNA pools.

NASA Discipline Developmental Biology↗
NASA NTRS1999

T cell activation responses are differentially regulated during clinorotation and in spaceflight

Studies of T lymphocyte activation with mitogenic lectins during spaceflight have shown a dramatic inhibition of activation as measured by DNA synthesis at 72 h, but the mechanism of this inhibition is unknown. We have investigated the progression of cellular events during the first 24 h of activation using both spaceflight microgravity culture and a ground-based model system that relies on the low shear culture environment of a rotating clinostat (clinorotation). Stimulation of human peripheral blood mononuclear cells (PBMCs) with soluble anti-CD3 (Leu4) in clinorotation and in microgravity culture shows a dramatic reduction in surface expression of the receptor for IL-2 (CD25) and CD69. An absence of bulk RNA synthesis in clinorotation indicates that stimulation with soluble Leu4 does not induce transition of T cells from G0 to the G1 stage of the cell cycle. However, internalization of the TCR by T cells and normal levels of IL-1 synthesis by monocytes indicate that intercellular interactions that are required for activation occur during clinorotation. Complementation of TCR-mediated signaling by phorbol ester restores the ability of PBMCs to express CD25 in clinorotation, indicating that a PKC-associated pathway may be compromised under these conditions. Bypassing the TCR by direct activation of intracellular pathways with a combination of phorbol ester and calcium ionophore in clinorotation resulted in full expression of CD25; however, only partial expression of CD25 occurred in microgravity culture. Though stimulation of purified T cells with Bead-Leu4 in microgravity culture resulted in the engagement and internalization of the TCR, the cells still failed to express CD25. When T cells were stimulated with Bead-Leu4 in microgravity culture, they were able to partially express CD69, a receptor that is constitutively stored in intracellular pools and can be expressed in the absence of new gene expression. Our results suggest that the inhibition of T cell proliferative response in microgravity culture is a result of alterations in signaling events within the first few hours of activation, which are required for the expression of important regulatory molecules.

NASA Experiment Number 9403079 1/2↗