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At least 73 records · Page 4

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NASA NTRS1975

Some studies of an unusual eucrite - Ibitira

The Ibitira eucrite is remarkable both for its vesicles and its unbrecciated nature. It consists of nearly 63 vol.% pyroxene (Wo14En38Fs48), 31% plagioclase (An95-96), nearly 2% of nickel-iron, troilite, ilmenite, titanian chromite, and 4% of a silica polymorph. It has a mean track density of 1.8 plus or minus 0.3 x 1,000,000 per sq cm, mainly due to cosmic rays. Its pre-atmospheric radius must have been at least 10 cm. The absence of complex radiation effects and presence of vesicles place constraints on the thickness of the Ibitira basalt flow. From the freezing time calculations of Provost and Bottinga, it appears that Ibitira came from a flow no less than 2.5 m and probably no more than 10 or 20 m thick. However, this estimate depends strongly on the viscosity of the melt, which is not well known.

Wilkening, L. L.↗

NASA NTRS1977

Analogies between respiration and a light-driven proton pump as sources of energy for active glutamate transport in Halobacterium halobium

Halobacterium halobium is known to contain sheets of bacteriorhodopsin, a pigment which upon exposure to light undergoes cyclic protonation and deprotonation, resulting in net H(+) translocation. In this paper, experiments were conducted to test H. halobium cell envelope vesicles for respiration-induced glutamate uptake. It is shown that glutamate transport in H. halobium cell envelope vesicles can occur as a result of respiration, as well as light acting on bacteriorhodopsin. Glutamate transport can be energized by the oxidation of dimethyl phenylenediamine, and the properties of the transport system are entirely analogous to those observed with illumination as the source of energy. In the case of respiration-dependent glutamate transport, the transportation is also driven by a Na(+) gradient, thereby confirming the existence of a single glutamate transport system independent of the source of energy. The analogy observed is indirect evidence that the cytochrome oxidase of H. halobium functions as a H(+) pump.

Belliveau, J. W.↗

NASA NTRS1976

Fluorine as a constituent in lunar magmatic gases

Fluorine surface deposits on Apollo 15 green glass, Apollo 17 orange glass, and on vesicle linings from Apollo 15 basalts were studied by a resonant nuclear reaction technique. Surface layers of about 10 to the 15th F atoms/sq cm were observed on unbroken spheroidal glass surfaces, whereas thinner (about 10 to the 14th atoms/sq cm) deposits were found on the vesicle linings.

Goldberg, R. H.↗

NASA NTRS1977

Experimental vaporization of the Holbrook chondrite

The vapor phase composition obtained by heating samples of the Holbrook L6 chondrite to 1300 C was determined quantitatively by Knudsen cell-quadrupole mass spectrometry. Maximum observed vapor pressures, produced at 1200 C, are reported for Na, K, Fe, and Ni, and the implications of the Na/K ratio are considered. The Fe and Ni data are discussed with attention to their migration in individual equilibrated chondrites. S2 (with minor SO2), H2O, and CO2 were also present in the high-temperature gas phase. Vesicles formed by the release of intrinsically derived volatiles are compared with vesicles in the Ibitira eucrite. Chondrite evolution is briefly discussed.

Gooding, J. L.↗

NASA NTRS1979

Gating effects in Halobacterium halobium membrane transport

The transport of Na(+) via an H(+)/Na(+) antiporter and of aspartate and serine via Na(+)/amino acid symport systems was studied in Halobacterium halobium cell envelope vesicles. Gradients for H(+) were produced by illuminating the bacteriorhodopsin-containing vesicles at different light intensities, and the rate and extent of Na(+) transport were followed as functions of the electrochemical potential difference for protons. The coupling of Na(+) and H(+) gradients suggested a translocation stoichiometry of 2H(+)/Na(+) for the antiporter. The rate of Na(+) transport increases steeply above a critical transmembrane electrochemical proton gradient, and since the electrical and the chemical potentials of H(+) at this threshold point vary with the experimental conditions, while the sum of these potentials is constant, it was concluded that the gating of the Na(+) transport is caused by the total electrochemical gradient.

Lanyi, J. K.↗

NASA NTRS1979

Light-driven solute transport in Halobacterium halobium

The cell membrane of Halobacterium halobium exhibits differential regions which contain crystalline arrays of a single kind of protein, termed bacteriorhodopsin. This bacterial retinal-protein complex resembles the visual pigment and, after the absorption of protons, translocates H(+) across the cell membrane, leading to an electrochemical gradient for protons between the inside and the outside of the cell. Thus, light is an alternate source of energy in these bacteria, in addition to terminal oxidation. The paper deals with work on light-driven transport in H. halobium with cell envelope vesicles. The discussion covers light-driven movements of H(+), Na(+), and K(+); light-driven amino acid transport; and apparent allosteric control of amino acid transport. The scheme of energy coupling in H. halobium vesicles appears simple, its quantitative details are quite complex and reveal regulatory phenomena. More knowledge is required of the way the coupling components are regulated by the ion gradients present.

Lanyi, J. K.↗

NASA NTRS1982

Magma vesiculation and pyroclastic volcanism on Venus

Theoretical consideration of the magma vesiculation process under observed and inferred venusian surface conditions suggests that vesicles should form in basaltic melts, especially if CO2 is the primary magmatic volatile. However, the high surface atmospheric pressure (about 90 bars) and density on Venus retard bubble coalescence and disruption sufficiently to make explosive volcanism unlikely. The products of explosive volcanism (fire fountains, convecting eruption clouds, pyroclastic flows, and topography-mantling deposits of ash, spatter, and scoria) should be rare on Venus, and effusive eruptions should dominate. The volume fraction of vesicles in basaltic rocks on Venus are predicted to be less than in chemically similar rocks on earth. Detection of pyroclastic landforms or eruption products on Venus would indicate either abnormally high volatile contents of Venus magmas (2.5-4 wt%) or different environmental conditions (e.g., lower atmospheric pressure) in previous geologic history.

Garvin, J. B.↗

NASA NTRS1982

Effect of disuse on sarcoplasmic reticulum in fast and slow skeletal muscle

The effect of 6 weeks of hindlimb immobilization on rat skeletal muscle sarcoplasmic reticulum (SR) was determined in the slow-twitch, type 1 soleus (SOL), the fast-twitch, type 2A deep region of the vastus lateralis (DVL), and the fast-twitch, type 2B superficial region of the vastus lateralis (SVL). Immobilization produced a significant decline in the Ca(2+) uptake rate (V sub max) of SR vesicles from the slow SOL, while the SR V sub max increased in the fast SVL and was unaltered in the DVL. Vesicles from the fast SVL and DVL also exhibited a higher total Ca(2+) uptake capacity following immobilization. An evaluation of the time course of the immobilization-mediated effect revealed an increased Ca(2+) uptake capacity in all three samples after 1 wk. In the SOL total Ca(2+) uptake returned to control level after 2 wk, while in the fast-twitch muscles the higher capacities were maintained. The Ca(2+)-stimulated SR ATPase activity was not altered in any of the muscle studies.

Kim, D. H.↗

NASA NTRS1984

Mineralogical comparison and cooling history of lunar and chondritic vesicular melt breccias

Lunar sample 77135, an impact melt breccia full of vesicles, has been reinvestigated by electron microprobe and X-ray diffraction techniques and compared with a vesicular melt LL chondrite, Yamato 790964, in an attempt to understand their impact heating processes and subsequent cooling history. Notable similarities between the lunar and chondritic melt breccias include: abundant vesicles, similar pyroxene chemical zoning trends, the presence of variable amounts of clastic material, and similar chemical compositions except for K and Na contents of glass and mesostasis. Some constraints on the cooling history are estimated from Mg-Fe diffusion profiles in olivine and pyroxene. The burial depth of lunar sample 77135 during cooling was 0.2-100 m; the depth for the chondrite was probably smaller. Impact melts were probably produced and a layer of regolith retained on the parent body sufficiently thick to allow the olivines to homogenize during slow cooling.

Miyamoto, M.↗

NASA NTRS1984

Concentrations and isotope ratios of carbon, nitrogen and sulfur in ocean-floor basalts

Ocean floor basalts studied from the Galapagos Ridge, FAMOUS area, Cayman Trough and Kilauea east rift contain 20-200 ppm carbon and 0.3-2.8 ppn nitrogen as sums of the vesicle-filling gases CO2 and N2 and dissolved species. The wide range of carbon contents found is due partly to the different extent of outgassing of vesicle-filling gases and partly to depth dependency of dissolved CO2 in the basalts. Sulfate commonly exists with sulfide in these basalts, and the sulfate/sulfide ratio increases with increasing water content, perhaps reflecting the higher oxidation potential in basalt melt of the higher water content.

Sakai, H.↗

NASA NTRS1988

Noble gases released by vacuum crushing of EETA 79001 glass

An EETA 79001 glass sample was crushed in a vacuum to observe the gases released. About 15 pct of the total gas concentrations were a mixture of a small amount of SPB-type gas with larger proportions of another air-like component. Less than 5 pct of the SPB gas was released by crushing, while 36-40 pct of the EETV (indigenous) gas was crush-released. The results are consistent with a siting of the EETV component in 10-100 micron vesicles seen in the glass. It is suggested that the SPB component is either in vesicles less than 6 microns in diameter or is primarily sited elsewhere.

Wiens, R. C.↗

NASA NTRS1993

The concentration and isotopic composition of carbon in basaltic glasses from the Juan de Fuca Ridge, Pacific Ocean

The abundance and C-13/C-12 ratios of carbon were analyzed in basaltic glass from twenty locations along the Juan de Fuca Ridge using a 3-step combustion/extraction technique. Carbon released during the first two combustion steps at 400-500 C and 600-650 C is interpreted to be secondary, and only the carbon recovered during a final combustion step at about 1200 C is thought to be indigenous to the samples. For carbon released at about 1200 C, glasses analyzed as 1-2 mm chips contained 23-146 ppm C with delta C-13 values of -4.8 to -9.3 per mil, whereas samples crushed to 38-63 microns or 63-90 microns yielded 56-103 ppm C with delta C-13 values of -6.1 to -9.2 per mil. The concentrations and isotopic compositions of the primary carbon dissolved in the glasses and present in the vesicles are similar to those previously reported for other ocean-ridge basalts. The Juan de Fuca basaltic magmas were not in equilibrium with respect to carbon when they erupted and quenched on the sea floor. Evidence of disequilibrium includes (1) a large range of carbon contents among glasses collected at similar depths, (2) a highly variable calculated carbon isotopic fractionation between melt and vapor determined by comparing crushed and uncrushed splits of the same sample, and (3) a lack of correlation between vesicle abundance, carbon concentration, and depth of eruption. Variations in carbon concentration and delta C-13 ratios along the ridge do not correlate with major element chemistry. The observed relationship between carbon concentrations and delta C-13 values may be explained by late-stage, variable degrees of open-system (Rayleigh-like) degassing.

Blank, Jennifer G.↗

NASA NTRS1988

Immunocytochemical localization of glutamic acid decarboxylase (GAD) and substance P in neural areas mediating motion-induced emesis: Effects of vagal stimulation on GAD immunoreactivity

Immunocytochemical methods were employed to localize the neurotransmitter amino acid gamma-aminobutyric acid (GABA) by means of its biosynthetic enzyme glutamic acid decarboxylase (GAD) and the neuropeptide substance P in the area postrema (AP), area subpostrema (ASP), nucleus of the tractus solitarius (NTS), and gelatinous nucleus (GEL). In addition, electrical stimulation was applied to the night vagus nerve at the cervical level to assess the effects on GAD-immunoreactivity (GAR-IR). GAD-IR terminals and fibers were observed in the AP, ASP, NTS, and GEL. They showed pronounced density at the level of the ASP and gradual decrease towards the solitary complex. Nerve cells were not labelled in our preparations. Ultrastructural studies showed symmetric or asymmetric synaptic contracts between labelled terminals and non-immunoreactive dendrites, axons, or neurons. Some of the labelled terminals contained both clear- and dense-core vesicles. Our preliminary findings, after electrical stimulation of the vagus nerve, revealed a bilateral decrease of GAD-IR that was particularly evident at the level of the ASP. SP-immunoreactive (SP-IR) terminals and fibers showed varying densities in the AP, ASP, NTS, and GEL. In our preparations, the lateral sub-division of the NTS showed the greatest accumulation. The ASP showed medium density of immunoreactive varicosities and terminals and the AP and GEL displayed scattered varicose axon terminals. The electron microscopy revealed that all immunoreactive terminals contained clear-core vesicles which make symmetric or asymmetric synaptic contact with unlabelled dendrites. It is suggested that the GABAergic terminals might correspond to vagal afferent projections and that GAD/GABA and substance P might be co-localized in the same terminal allowing the possibility of a regulated release of the transmitters in relation to demands.

GABA↗

NASA NTRS1994

Formation and vesiculation of biomembranes during spaceflight

Shuttle flight, sounding rocket flight, and parabolic flight experiments demonstrate the formation of bilayer membrane vesicles (liposomes) in reduced gravity, following the dilution of detergent from detergent-phospholipid mixed micelles. The reduction in detergent concentration initiates assembly of bilayer membrane sheets, which are sensitive to solution disturbances. An increase in disturbances by forced dilution results in small diameter liposomes (less than 150 nm), in both ground and flight samples. In the absence of forced dilution, liposomes remain small at 1-g, but exhibit much larger diameters at 0-g (1000-2000 nm). Our spaceflight data reveal that membrane assembly and vesiculation are strongly influenced by gravity-induced solution disturbances (e.g., convection currents), which limit vesicle diameter.

Claassen, Dale E.↗

NASA NTRS1994

Structure and functions of simple membrane-water interfaces

The structure and functions of the earliest ancestors of contemporary cells are focal points in studies of the origin of life. Probably the first cell-like structures were vesicles - closed, spheroidal structures with aqueous medium trapped inside. The membranous walls of vesicles were most likely bilayers composed of simple amphiphilic material available on early earth. The membrane studied was composed of glycerol 1-monooleate (GMO). Glycerol forms the polar head group and the oily tail contains 18 carbon atoms. All head groups have been found to be located in two narrow regions at the interfaces with water. The membrane interior, formed by the hydrophobic tails, is quite fluid with chain disorder increasing towards the center of the bilayer. These results are in agreement with x-ray and neutron scattering data from related bilayers. The width of the membrane is not constant, but fluctuates in time and space. Occasional thinning defects in the membrane, observed during the course of the simulations, may have a significant influence on rates of passive transport of small molecules across membranes. It has been found that water penetrates the head group region but not the oily interior of the membrane. Water molecules near the interface are oriented by dipoles of the head groups. The resulting electrostatic potential across the interface, determined in our simulations, has been found to be markedly larger than across the water-oil interface. This quantity has been implicated as the source of selectivity, with respect to the sign of the charge, as an ion approaches the interface and during transport of hydrophobic ions across membranes.

Pohorille, A.↗

NASA NTRS1994

Experiment K-7-28: Lung Morphology Study

There are no previous studies investigating the effect of microgravity exposure during spaceflight on lung tissue. We examined the ultrastructure of the left lungs of 5 Czechoslovakian Wistar rats flown on the 13 day, 19+ hr. Cosmos 2044 mission, and compared them to 5 vivarium and 5 synchronous controls at 1-g conditions, and 5 rats exposed to 14 days of tail-suspension. Within 10 minutes of sacrifice by decapitation, the lungs were removed and immersed in 3% glutaraldehyde in 0.1M phosphate buffer (total osmolarity of the fixative: 560 mOsm; pH = 7.4). The tissue stored at 5 C was transported to our laboratory where it was processed for light and electron microscopy. No significant perivascular cuffing caused by interstitial edema was present in the tissue samples. Some of the flight, tail-suspended, and synchronous control rats showed alveolar edema, while vivarium controls did not. The pulmonary capillaries appeared to be more congested in the flight animals than in the other groups. This could be related to the increased hematocrit due to the microgravity exposure. In all 5 flight, 4 tail-suspended, and 3 synchronous rats, red blood cells (RBC) were present in the alveolar spaces. The RBC were either suspended free in the alveoli or observed lining the alveolar wall. The frequency of RBC lining the alveolar walls appeared greater in the dorsal (gravity non-dependent) than in ventral (gravity dependent) regions of the lung in these three animal groups. In 3 of the vivarium controls, a few RBC were found in the alveolar spaces. Intra-capillary fluid-filled vesicles were observed in the flight, tail-suspended and synchronous animals, but not in the vivarium controls. The formation of intra-capillary fluid-filled vesicles has been previously associated with pulmonary hypertension induced by high altitude exposure and mitral stenosis. In conclusion, pulmonary hemorrhage and alveolar edema of unknown origin occurred to a greater extent in the flight, tail-suspended, and synchronous control animals, and in the dorsal regions of the lung when compared to the vivarium controls. The etiology of these changes, which are possibly due to an increase in pulmonary vascular pressure, requires further investigation.

West, J. B.↗

NASA NTRS1984

The Structure of the Mammalian Area Postrema

The area postrema in mammals other than rodents and lagomorphs is a bilateral mound of gelatinous-appearing tissue that protrudes into the caudal fourth ventricle on either side of the obex. In rodents and lagomorphs it is a single midline structure at the apex of the calamus scriptorius. The vasculature is derived mainly from the posterior inferior cerebellar arteries and consists mainly of sinusoidal capillaries. It appears to constitute a portal system, at least in the rat. Many of the capillaries are fenestrated, and many large perivascular spaces with both vascular and parenchymal basal laminae are present. The cell population is composed of flattened ependymal cells exhibiting microvilli, and of small neurons, normal astrocytes, glialoid cells, and a very few oligodendroglia. Mast cells are occasionally present. The glialoid cells appear to be the predominant cell type and exhibit great numbers of vascular podia. Axodendritic synapses are numerous and axosomatic synapses are occasionally seen in the parenchyma. Synaptic vesicles are mainly of the clear-cored type but large dense-cored vesicles are commonly observed in some axon terminals.

Brizzee, K. R.↗

NASA NTRS2004

The First Cell Membranes

Organic compounds are synthesized in the interstellar medium and can be delivered to planetary surfaces such as the early Earth, where they mix with endogenous organic mixtures. Some of these compounds are amphiphilic, having polar and non-polar groups on the same molecule. Amphiphilic compounds spontaneously self-assembly into more complex structures such as bimolecular layers, which in turn form closed membranous vesicles. The first forms of cellular life required self-assembled membranes that were likely to be available on the prebiotic Earth. Laboratory simulations show that such vesicles readily encapsulate functional macromolecules, including nucleic acids and polymerases. A goal of future investigations is to fabricate artificial cells as models of the origin of life.

Deamer, David↗