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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Polyamines as Possible Modulators of Gravity-induced Calcium Transport in Plants

Data from various laboratories indicate a probable relationship between calcium movement and some aspects of graviperception and tropistic bending responses. The movement of calcium in response to gravistimulation appears to be rapid, polar and opposite in direction to polar auxin transport. What might be the cause of such rapid Ca(2+) movement? Data from studies on polyamine (PA) metabolism may furnish a clue. A transient increase in the activity of ornithine decarboxylase (ODC) and titers of various PAs occurs within 60 seconds after hormonal stimulation of animal cells, followed by Ca(2+) transport out of the cells. Through the use of specific inhibitors, it was shown that the enhanced PA synthesis from ODC was essential not only for Ca(2+) transport, but also for Ca(2+) transport-dependent endocytosis and the movement of hexoses and amino acids across the plasmalemma. In plants, rapid changes in arginine decarboxylase (ADC) activity occur in response to various plant stresses. Physical stresses associated with gravisensor displacement and reorientation of a plant in the gravitational field could similarly activate ADC and that resultant increases in PA levels might initiate transient perturbations in Ca(2+) homeostasis.

Galston, A. W.↗
NASA NTRS1993

Allowable exposure limits for carbon dioxide during extravehicular activity

The intent was to review the research pertaining to human exposure to carbon dioxide (CO2) and to recommend allowable exposure limits for extravehicular activity (EVA). Respiratory, renal, and gastrointestinal systems may be adversely affected by chronic low dose CO2 exposure. Ventilation was increased 15 percent with 1 percent CO2 and 50 percent with 2 percent CO2. Chronic exposure to less than 2 percent CO2 led to 20 day cycles of uncompensated and compensated respiratory acidosis. Acid-base changes were small. Histopathologic changes in guinea pig lungs have been noted with long term exposure to 1 percent CO2. No changes were seen with exposure to 0.5 percent CO2. Cycling of bone calcium stores with associated changes in blood and urinary calcium levels occurs with long term CO2 exposure. Histologic changes in bone have been noted in guinea pigs exposed to 1 percent CO2. Renal calcification has been noted in guinea pigs with exposure to as low as 0.5 percent CO2. An increase in gastric acidity was noted in subjects with long term exposure to 1 percent CO2. Cardiovascular and neurologic function were largely unaffected. A decrease in the incidence of respiratory, renal, and gastrointestinal disease was noted in submariners coincident with a decrease in ambient CO2 from 1.2 percent to 0.8-0.9 percent. Oxygen (O2) and CO2 stimulate respiration independently and cumulatively. The addition of CO2 to high dose O2 led to the faster onset of seizure activity in mice. Experiments evaluating the physiologic responses to intermittent, repetitive exposures to low dose CO2 and 100 percent O2 mixtures should be performed. A reduction in the current NASA standard for CO2 exposure during EVA of 1 percent (7.6 mmHg) for nominal and 2 percent (15.2 mmHg) for heavy exertion to 0.5 percent (3.8 mmHg) for nominal and 1 percent (7.6 mmHg) for heavy exertion may be prudent. At a minimum, the current NASA standard should not be liberalized.

Seter, Andrew J.↗
NASA NTRS1988

Insulin effect on amino acid uptake by unloaded rat hindlimb muscles

The effect of insulin on the uptake of alpha-amino-isobutyric acid (AIB) by unloaded rat hindlimb muscles was investigated using soleus and extensor digitorum longus (EDL) muscles from intact and adrenalectomized (ADX) rats that were tail-casted for six days. It was found that, at insulin levels above 0.00001 units/ml, the in vitro rate of AIB uptake by muscles from intact animals was stimulated more in the weight bearing muscles than in unloaded ones. In ADX animals, this differential response to insulin was abolished.

Jaspers, S. R.↗
NASA NTRS1984

Tomato growth as affected by root-zone temperature and the addition of gibberellic acid and kinetin to nutrient solutions

The effect of root-zone temperature on young tomato plants (Lycopersicon esculentum Mill. cv. Heinz 1350) was evaluated in controlled environments using a recirculating solution culture system. Growth rates were measured at root-zone temperatures of 15 degrees, 20 degrees, 25 degrees, and 30 degrees C in a near optimum foliar environment. Optimum growth occurred at 25 degrees to 30 degrees during the first 4 weeks of growth and 20 degrees to 25 degrees during the 5th and 6th weeks. Growth was severely restricted at 15 degrees. Four concentrations of gibberellic acid (GA3) and kinetin were added to the nutrient solution in a separate trial; root-zone temperature was maintained at 15 degrees and 25 degrees. Addition of 15 micromoles GA3 to solutions increased specific leaf area, total leaf area, and dry weight production of plants in both temperature treatments. GA3-induced growth stimulation was greater at 15 degrees than at 25 degrees. GA3 may promote growth by increasing leaf area, enhancing photosynthesis per unit leaf area, or both. Kinetic was not useful in promoting growth at either temperature.

NASA Program CELSS↗
NASA NTRS1999

AV3V lesions attenuate the cardiovascular responses produced by blood-borne excitatory amino acid analogs

Systemic injections of the excitatory amino acid (EAA) analogs, kainic acid (KA) and N-methyl-D-aspartate (NMDA), produce a pressor response in conscious rats that is caused by a centrally mediated activation of sympathetic drive and the release of arginine vasopressin (AVP). This study tested the hypothesis that the tissue surrounding the anteroventral part of the third ventricle (AV3V) plays a role in the expression of the pressor responses produced by systemically injected EAA analogs. Specifically, we examined whether prior electrolytic ablation of the AV3V region would affect the pressor responses to KA and NMDA (1 mg/kg iv) in conscious rats. The KA-induced pressor response was smaller in AV3V-lesioned than in sham-lesioned rats (11 +/- 2 vs. 29 +/- 2 mmHg; P < 0.05). After ganglion blockade, KA produced a pressor response in sham-lesioned but not AV3V-lesioned rats (+27 +/- 3 vs. +1 +/- 2 mmHg; P < 0.05). The KA-induced pressor response in ganglion-blocked sham-lesioned rats was abolished by a vasopressin V1-receptor antagonist. Similar results were obtained with NMDA. The pressor response to AVP (10 ng/kg iv) was slightly smaller in AV3V-lesioned than in sham-lesioned ganglion-blocked rats (45 +/- 3 vs. 57 +/- 4 mmHg; P < 0.05). This study demonstrates that the pressor responses to systemically injected EAA analogs are smaller in AV3V-lesioned rats. The EAA analogs may produce pressor responses by stimulation of EAA receptors in the AV3V region, or the AV3V region may play an important role in the expression of these responses.

Non-NASA Center↗
NASA NTRS1985

Role of carbonic anhydrase in bone resorption induced by 1,25 dihydroxyvitamin D3 in vitro

The calvaria of 5-to-6-day-old mice treated with 1 x 10 to the -8th M of 1,25(OH)2D3 in vitro for 48 hours are examined in order to study the function of carbonic anhydrase in bone resorption. Calcium concentrations in the culture were measured to assess bone resorption. It is observed that 1,25(OH)2D3 effectively stimulates bone resorption in vitro and the resorption is dose-dependent. The effects of azetazolamide on 1,25(OH)2D3-induced bone resorption are investigated. The data reveal that 1,25(OH)2D3-induced calcium release is associated with an increase in the carbonic anhydrase activity of bone, and bone alkaline phosphatase activity is decreased and acid phosphatase activity is increased in response to 1,25(OH)2D3. A two-fold mechanism for 1,25(OH)2D3-induced bone resorption is proposed; the first mechanism is an indirect activation of osteoclasts and the second involves an interaction between hormone and osteoclast precursors.

Hall, G. E.↗
NASA NTRS1995

Gamma-interferon causes a selective induction of the lysosomal proteases, cathepsins B and L, in macrophages

Previous studies have indicated that acid-optimal cysteine proteinase(s) in the endosomal-lysosomal compartments, cathepsins, play a critical role in the proteolytic processing of endocytosed proteins to generate the antigenic peptides presented to the immune system on major histocompatibility complex (MHC) class II molecules. The presentation of these peptides and the expression of MHC class II molecules by macrophages and lymphocytes are stimulated by gamma-interferon (gamma-IFN). We found that treatment of human U-937 monocytes with gamma-IFN increased the activities and the content of the two major lysosomal cysteine proteinases, cathepsins B and L. Assays of protease activity, enzyme-linked immunosorbant assays (ELISA) and immunoblotting showed that this cytokine increased the amount of cathepsin B 5-fold and cathepsin L 3-fold in the lysosomal fraction. By contrast, the aspartic proteinase, cathepsin D, in this fraction was not significantly altered by gamma-IFN treatment. An induction of cathepsins B and L was also observed in mouse macrophages, but not in HeLa cells. These results suggest coordinate regulation in monocytes of the expression of cathepsins B and L and MHC class II molecules. Presumably, this induction of cysteine proteases contributes to the enhancement of antigen presentation by gamma-IFN.

Non-NASA Center↗
NASA NTRS1984

Thigmomorphogenesis: the relationship of mechanical perturbation to elicitor-like activity and ethylene production

An extracellular solution obtained from bean (Phaseolus vulgaris L. cv. Resistant Cherokee Wax) stems induced phytoalexin-like substance and ethylene production in a soybean [Glycine max (L.) Merr. cv. Wayne] cotyledon bioassay. The elicitor-like activity for phytoalexin formation and ethylene production was increased by mechanical perturbation of bean stems. Moreover, the application of extracted or known elicitors to bean plants mimicked the effect of mechanical perturbation (i.e., inhibition of stem elongation and enhancement of radial growth). The effects of extract when applied exogenously, on elicitor-like activity in the bioassay as well as stem thickening were decreased by aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis. These results suggest that elicitor-like substances which are formed in response to mechanical perturbation contribute to the thigmomorphogenesis.

Plants, Medicinal↗
NASA NTRS1992

The role of calcium in growth induced by indole-3-acetic acid and gravity in the leaf-sheath pulvinus of oat (Avena sativa)

Leaf-sheath pulvini of excised segments from oat (Avena sativa L.) were induced to grow by treatment with 10 micromoles indole-3-acetic acid (IAA), gravistimulation, or both, and the effects of calcium, EGTA, and calcium channel blockers on growth were evaluated. Unilaterally applied calcium (10 mM CaCl2) significantly inhibited IAA-induced growth in upright pulvini but had no effect on growth induced by either gravity or gravity plus IAA. Calcium alone had no effect on upright pulvini. The calcium chelator EGTA alone (10 mM) stimulated growth in upright pulvini. However, EGTA had no effect on either IAA- or gravity-induced growth but slightly diminished growth in IAA-treated gravistimulated pulvini. The calcium channel blockers lanthanum chloride (25 mM), verapamil (2.5 mM), and nifedipine (2.5 mM) greatly inhibited growth as induced by IAA (> or = 50% inhibition) or IAA plus gravity (20% inhibition) but had no effect on gravistimulated pulvini. Combinations of channel blockers were similar in effect on IAA action as individual blockers. Since neither calcium ions nor EGTA significantly affected the graviresponse of pulvini, we conclude that apoplastic calcium is unimportant in leaf-sheath pulvinus gravitropism. The observation that calcium ions and calcium channel blockers inhibit IAA-induced growth, but have no effect on gravistimulated pulvini, further supports previous observations that gravistimulation alters the responsiveness of pulvini to IAA.

Non-NASA Center↗
NASA NTRS1994

An Arg-Gly-Asp peptide stimulates Ca2+ efflux from osteoclast precursors through a novel mechanism

We examined the effect of a peptide containing the Arg-Gly-Asp (RGD) sequence on 45Ca2+ efflux from osteoclast precursors. 45Ca(2+)-loaded osteoclast precursors were treated with GRGDSP (170 microM) for 10 min after 30 min of basal perfusion with a bicarbonate-containing buffer. GRGDSP significantly increased fractional efflux of Ca2+ from treated cells compared with vehicle-treated cells (P < 0.01) or cells treated with up to 200 micrograms/ml of a control peptide containing GRGESP. The effect of RGD was sustained for 15 min after the peptide was removed from the perfusate, but control levels of Ca2+ efflux returned by 1 h. The Ca2+ efflux effect of GRGDSP was most likely due to activation of the plasma membrane Ca(2+)-adenosinetriphosphatase (Ca(2+)-ATPase) pump, as indicated by its inhibition with vanadate and a calmodulin antagonist, N-(4-aminobutyl)-5-chloro-2-naphthalenesulfonamide, and the absence of an effect of Na+/Ca2+ exchange inhibition. An inhibitor of cyclic nucleotide-dependent protein kinases, N-[2-(methylamino)ethyl]-5-isoquinoline-sulfonamide (0.1 mM), failed to inhibit GRGDSP-stimulated Ca2+ efflux. However, genistein and herbimycin A, inhibitors of protein-tyrosine kinases, blocked Ca2+ efflux stimulated by GRGDSP. The results indicate that RGD sequences of matrix proteins may stimulate Ca2+ efflux from osteoclasts through activation of protein-tyrosine kinases and suggest that GRGDSP-stimulated Ca2+ efflux is mediated via the plasma membrane Ca(2+)-ATPase.

NASA Discipline Musculoskeletal↗
NASA NTRS1999

Alterations in Skeletal Muscle Function with Microgravity, and the Protective Effects of High Resistance Isometric and Isotonic Exercise

Exposure to microgravity or models designed to mimic the unloaded condition, such as bed rest in humans and hindlimb unloading (HU) in rats leads to skeletal muscle atrophy, a loss in peak force and power, and an increased susceptibility to fatigue. The posterior compartment muscles of the lower leg (calf muscle group) appear to be particularly susceptible. Following only 1 wk in space or HU, rat soleus muscle showed a 30 to 40% loss in wet weight. After 3 wk of HU, almost all of the atrophied soleus fibers showed a significant increase in maximal shortening velocity (V(sub 0)), while only 25 to 30 % actually transitioned to fast fibers. The increased V(sub 0), was protective in that it reduced the decline in peak power associated with the reduced peak force. When the soleus is stimulated in situ following HU or zero-g one observes an increased rate and extent of fatigue, and in the former the increased fatigue is associated with a more rapid depletion of muscle glycogen and lactate production. Our working hypothesis is that following HU or spaceflight in rats and bed rest or spaceflight in humans limb skeletal muscles during contractile activity depend more on carbohydrates and less on fatty acids for their substrate supply. Baldwin et al. found 9 days of spaceflight to reduce by 37% the ability of both the high and low oxidative regions of the vastus muscle to oxidize long-chain fatty acids. This decline was not associated with any change in the enzymes of the tricarboxylic acid cycle or oxidation pathway. The purpose of the current research was to establish the extent of functional change in the slow type I and fast type H fibers of the human calf muscle following 17 days of spaceflight, and determine the cellular mechanisms of the observed changes. A second goal was to study the effectiveness of high resistance isotonic and isometric exercise in preventing the deleterious functional changes associated with unloading.

Fitts, R. H.↗
NASA NTRS1988

Effect of chronic d-fenfluramine administration on rat hypothalamic serotonin levels and release

D-fenfluramine, an anorectic agent in rats and man, was administered daily at doses 1.25, 2.5, 5, or 10 mg/kg/day for 10 days, and sacrificed 6 days later. Hypothalamic serotonin (5-HT) levels were unchanged in rats receiving 1.25-5 mg/kg/day of d-fenfluramine but reduced by 22 percent (p less than 0.01) at the highest drug dose (10 mg/kg/day); hypothalamic 5-hydroxyindole acetic acid (5-HIAA) levels were reduced by 15 percent (p less than 0.05) or 28 percent (p less than 0.01) in rats receiving 5 or 10 mg/kg/day of the drug, respectively. Hypothalamic slices prepared from rats which were previously treated with any of the drug doses spontaneously released endogenous 5-HT at rates that did not differ from those of vehicle-treated rats. 5-HT released with electrical field-stimulation was unaffected by prior d-fenfluramine treatment at doses of 1.25-5 mg/kg/day, and was reduced by 20 percent (p less than 0.05) from slices prepared from rats which received 10 mg/kg/day. 5-HIAA efflux was also attenuated by the highest drug dose. These data indicate that chronic administration to rats of customary anorectic doses of d-fenfluramine (i.e. 0.06-1.25 mg/kg) fail to cause long-lasting reductions in brain 5-HT release.

Schaechter, Judith D.↗
NASA NTRS1986

In vitro and in vivo protein phosphorylation in Avena sativa L. coleoptiles: effects of Ca2+, calmodulin antagonists, and auxin

In vitro and in vivo protein phosphorylations in oat (Avena sativa L.) coleoptile segments were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and by two-dimensional gel electrophoresis. In vitro phosphorylation of several polypeptides was distinctly promoted at 1 to 15 micromolar free Ca2+ concentrations. Ca2(+)-stimulated phosphorylation was markedly reduced by trifluoperazine, chlorpromazine, and naphthalene sulfonamide (W7). Two polypeptides were phosphorylated both under in vitro and in vivo conditions, but the patterns of phosphorylation of several other polypeptides were different under the two conditions indicating that the in vivo phosphorylation pattern of proteins is not truly reflected by in vitro phosphorylation studies. Trifluoperazine, W7, or ethylene glycol-bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) + calcium ionophore A23187 treatments resulted in reduced levels of in vivo protein phosphorylation of both control and auxin-treated coleoptile segments. Analysis by two-dimensional electrophoresis following in vivo phosphorylation revealed auxin-dependent changes of certain polypeptides. A general inhibition of phosphorylation by calmodulin antagonists suggested that both control and auxin-treated coleoptiles exhibited Ca2+, and calmodulin-dependent protein phosphorylation in vivo.

NASA Discipline Plant Biology↗
NASA NTRS1984

Response to gravity by Zea mays seedlings. I. Time course of the response

Gravistimulation induces an asymmetric distribution of free indole-3-acetic acid (IAA) in the cortex-epidermis of the Zea mays L. cv 'Stowells Evergreen' mesocotyl within 15 minutes, the shortest time tested. IAA was measured by an isotope dilution method as the pentaflurobenzyl ester. The per cent IAA in the lower half of the mescotyl cortex was 56 to 57% at 15, 30, and 90 minutes after stimulus initiation. Curvature is detectable in the mescotyl within 3 minutes after beginning gravitropic stimulation. The rate of curvature of the mesocotyl increases during the first 60 minutes to maximum of about 30 degrees per hour. Thus, the growth asymmetry continues to increase for 45 minutes after hormone asymmetry is established. Free IAA occurs predominantly in the stele of the mesocotyl whereas esterified IAA is mainly in the mesocotyl cortex-epidermis. This compartmentation may permit determining in which tissue the hormone asymmetry arises. Current data suggest the asymmetry originated in the stele.

Gravitation↗
NASA NTRS2003

Caspase inhibitors promote vestibular hair cell survival and function after aminoglycoside treatment in vivo

The sensory hair cells of the inner ear undergo apoptosis after acoustic trauma or aminoglycoside antibiotic treatment, causing permanent auditory and vestibular deficits in humans. Previous studies have demonstrated a role for caspase activation in hair cell death and ototoxic injury that can be reduced by concurrent treatment with caspase inhibitors in vitro. In this study, we examined the protective effects of caspase inhibition on hair cell death in vivo after systemic injections of aminoglycosides. In one series of experiments, chickens were implanted with osmotic pumps that administrated the pan-caspase inhibitor z-Val-Ala-Asp(Ome)-fluoromethylketone (zVAD) into inner ear fluids. One day after the surgery, the animals received a 5 d course of treatment with streptomycin, a vestibulotoxic aminoglycoside. Direct infusion of zVAD into the vestibule significantly increased hair cell survival after streptomycin treatment. A second series of experiments determined whether rescued hair cells could function as sensory receptors. Animals treated with streptomycin displayed vestibular system impairment as measured by a greatly reduced vestibulo-ocular response (VOR). In contrast, animals that received concurrent systemic administration of zVAD with streptomycin had both significantly greater hair cell survival and significantly increased VOR responses, as compared with animals treated with streptomycin alone. These findings suggest that inhibiting the activation of caspases promotes the survival of hair cells and protects against vestibular function deficits after aminoglycoside treatment.

NASA Discipline Neuroscience↗
NASA NTRS2024

Toward Prebiotic Chemistry on Titan: Impact Experiments on Organic Haze Particles

Impacts are critical to producing the aqueous environments necessary to stimulate prebiotic chemistry on Titan's surface. Furthermore, organic hazes resting on the surface are a likely feedstock of biomolecules. In this work, we conduct impact experiments on laboratory-produced organic haze particles and haze/sand mixtures and analyze these samples for life's building blocks. Samples of unshocked haze and sand particles are also analyzed to determine the change in biomolecule concentrations and distributions from shocking. Across all samples, we detect seven nucleobases, nine proteinogenic amino acids, and five other biomolecules (e.g., urea) using a blank subtraction procedure to eliminate signals due to contamination. We find that shock pressures of 13 GPa variably degrade nucleobases, amino acids, and a few other organics in haze particles and haze/sand mixtures; however, certain individual biomolecules become enriched or are even produced from these events. Xanthine, threonine, and aspartic acid are enriched or produced in impact experiments containing sand, suggesting these minerals may catalyze the production of these biomolecules. On the other hand, thymine and isoleucine/norleucine are enriched or produced in haze samples containing no sand, suggesting catalytic grains are not necessary for all impact shock syntheses. Uracil, glycine, proline, cysteine, and tyrosine are the most unstable to impact-related processing. These experiments suggest that impacts alter biomolecule distributions on Titan's surface, and that organic hazes co-occurring with fine-grained material on the surface may provide an initial source for further prebiotic chemistry on Titan.

impact experiments↗
NASA NTRS2003

Complex formation by the human Rad51B and Rad51C DNA repair proteins and their activities in vitro

The human Rad51 protein is essential for DNA repair by homologous recombination. In addition to Rad51 protein, five paralogs have been identified: Rad51B/Rad51L1, Rad51C/Rad51L2, Rad51D/Rad51L3, XRCC2, and XRCC3. To further characterize a subset of these proteins, recombinant Rad51, Rad51B-(His)(6), and Rad51C proteins were individually expressed employing the baculovirus system, and each was purified from Sf9 insect cells. Evidence from nickel-nitrilotriacetic acid pull-down experiments demonstrates a highly stable Rad51B.Rad51C heterodimer, which interacts weakly with Rad51. Rad51B and Rad51C proteins were found to bind single- and double-stranded DNA and to preferentially bind 3'-end-tailed double-stranded DNA. The ability to bind DNA was elevated with mixed Rad51 and Rad51C, as well as with mixed Rad51B and Rad51C, compared with that of the individual protein. In addition, both Rad51B and Rad51C exhibit DNA-stimulated ATPase activity. Rad51C displays an ATP-independent apparent DNA strand exchange activity, whereas Rad51B shows no such activity; this apparent strand exchange ability results actually from a duplex DNA destabilization capability of Rad51C. By analogy to the yeast Rad55 and Rad57, our results suggest that Rad51B and Rad51C function through interactions with the human Rad51 recombinase and play a crucial role in the homologous recombinational repair pathway.

Non-NASA Center↗
NASA NTRS1996

Gravitational loading of a simulated launch alters mRNA expression in osteoblasts

Serum-deprived mouse osteoblastic cells (MC3T3-E1a) were centrifuged under a regime designed to simulate a space shuttle launch (maximum of 3g). Messenger RNA levels for eight genes involved in bone growth and maintenance were determined using RT-PCR. Following 30 min of centrifugation, mRNA level for early response gene c-fos was significantly increased 89% (P < 0.05). The c-fos induction was transient and returned to control levels after 3 h. The mRNA level for the mineralization marker gene osteocalcin was significantly decreased to 44% of control level (P < 0.005) 3 h after centrifugation. No changes in mRNA levels were detected for c-myc, TGFbeta1, TGFbeta2, cyclophilin A, or actin. No basal mRNA level for TGFbeta3 was detected. In addition, no change in the steady-state synthesis of prostaglandin E2 was detected, possibly due to lack of lipid substrates in serum-deprived cells, suggesting that the increase in c-fos mRNA in response to gravitational loading is a result of mechanical stimulation. These results indicate that a small magnitude mechanical loading, such as that experienced during a shuttle launch, can alter mRNA levels in quiescent osteoblastic cells.

Non-NASA Center↗