PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “NASA Discipline Number 40-99”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

29 records · Page 2Linked to original sources
PubMed1991

The role of extracellular free-calcium gradients in gravitropic signalling in maize roots.

Gravitropism in roots has been proposed to depend on a downward redistribution of calcium across the root cap. However, because of the many calcium-binding sites in the apoplast, redistribution might not result in a physiologically effective change in the apoplasmic calcium activity. To test whether there is such a change, we measured the effect of gravistimulation on the calcium activity of statocyte cell walls with calcium-specific microelectrodes. Such a measurement must be made on a tissue with gravity sensing cells at the surface. To obtain such a tissue, decapped maize roots (Zea mays L. cv. Golden Cross Bantam) were grown for 31 h to regenerate gravitropic sensitivity, but not root caps. The calcium activity in the apoplasm surrounding the gravity-sensing cells could then be measured. The initial pCa was 2.60 +/- 0.28 (approx 2.5 mM). The calcium activity on the upper side of the root tip remained constant for 10 min after gravistimulation, then decreased 1.7-fold. On the lower side, after a similar lag the calcium activity increased 1.6-fold. Control roots, which were decapped but measured before recovering gravisensitivity (19 h), showed no change in calcium activity. To test whether this gradient is necessary for gravitropic curvature, we eliminated the calcium activity gradient during gravitropism by applying a mobile calcium-binding site (dinitro-BAPTA; 1,2-bis(2-amino-5-nitro-phenoxy)ethane-N,N,N',N'-tetraacetic acid) to the root cap; this treatment eliminated gravicurvature. A calcium gradient may be formed by proton-induced calcium desorption if there is a proton gradient. Preventing the formation of apoplastic pH gradients, using 10 and 50 mM 2-(N-morpholino)ethanesulfonic acid (Mes) buffer or 10 mM fusicoccin to stimulate proton excretion maximally, did not inhibit curvature; therefore the calcium gradient is not a secondary effect of a proton gradient. We have found a distinct and rapid differential in the apoplasmic calcium activity between the upper and lower sides of gravistimulated maize root tips which is necessary for gravitropism.

Biological Transport↗
PubMed1988

Competency for graviresponse in the leaf-sheath pulvinus of Avena sativa: onset to loss.

The development of the leaf-sheath pulvinus of oat (Avena sativa L. cv. Victory) was studied in terms of its competency to respond to gravistimulation. Stages of onset of competency, maximum competency and loss of competency were identified, using the length of the supertending internode as a developmental marker. During the early phases in the onset of competency, the latency period between stimulus and graviresponse decreased and the steady state response rate increased significantly. When fully competent, the latency period remained constant as the plant continued to develop, suggesting that the latency period is relatively insensitive to quantitative changes (e.g., in carbohydrate or nutrient availability) at the cell level within the plant. In contrast, the response rate was found to increase with plant development, indicating that graviresponse rate is more strongly influenced by quantitative cellular changes. The total possible graviresponse of a single oat pulvinus was confirmed to be significantly less than the original presentation angle. This was shown to not result from a loss of competency, since the graviresponse could be reinitiated by increasing the presentation angle. As a result of the low overall graviresponse of individual pulvini, two or more pulvini are required to bring the plant apex to the vertical. This was determined to occur though the sequential, rather than simultaneous, action of successive pulvini, since a given pulvinus lost competency to gravirespond shortly after the next pulvinus became fully competent.

Avena↗
PubMed1987

How cereal grass shoots perceive and respond to gravity.

The leaf-sheath pulvinus of grasses presents a unique system for studying gravitropism, primarily because of its differences from other organs. The mature pulvinus is a discrete organ specialized for gravitropism: it is nongrowing in the absence of gravistimulation and capable of displaying a graviresponse independent of the rest of the plant. In this paper we present a model for gravitropism in pulvini based on recent findings from studies on the mechanisms of graviperception and graviresponse. According to this model, amyloplasts play an essential role in perceiving a change in the orientation of the pulvinus. The perception of this reorientation leads to the enhanced synthesis and release from conjugate of the auxin IAA, and the increased conjugation of gibberellin, on a localized basis. Because there is a graded growth promotion across the gravistimulated pulvinus, it is suggested that the observed hormonal asymmetry is actually an indication of a linear gradient of hormone concentration, as well as hormone response, across the pulvinus. It is further suggested that the linear gradient of hormone concentration may be predominantly the result of local changes in hormone level, rather than a product of hormonal movement into or across the pulvinus.

Edible Grain↗
PubMed1996

The delayed rectifier, IKI, is the major conductance in type I vestibular hair cells across vestibular end organs.

Hair cells were dissociated from the semicircular canal, utricle, lagena and saccule of white king pigeons. Type I hair cells were identified morphologically based on the ratios of neck width to cuticular plate width (NPR < 0.72) as well as neck width to cell body width (NBR < 0.64). The perforated patch variant of the whole-cell recording technique was used to measure electrical properties from type I hair cells. In voltage-clamp, the membrane properties of all identified type I cells were dominated by a predominantly outward potassium current, previously characterized in semicircular canal as IKI. Zero-current potential, activation, deactivation, slope conductance, pharmacologic and steady-state properties of the complex currents were not statistically different between type I hair cells of different vestibular end organs. The voltage dependence causes a significant proportion of this conductance to be active about the cell's zero-current potential. The first report of the whole-cell activation kinetics of the conductance is presented, showing a voltage dependence that could be best fit by an equation for a single exponential. Results presented here are the first data from pigeon dissociated type I hair cells from utricle, saccule and lagena suggesting that the basolateral conductances of a morphologically identified population of type I hair cells are conserved between functionally different vestibular end organs; the major conductance being a delayed rectifier characterized previously in semicircular canal hair cells as IKI.

4-Aminopyridine↗
PubMed1994

Gravity effects on membrane processes.

Application of the Gouy-Chapman-Debye-Hückel (GCDH) theory to a model membrane in contact with electrolytes of various concentrations and composition predict density variations within an interfacial layer. Assuming that on cellular dimensions hydrodynamics can be applied (the objections are briefly discussed) two types of gravity effects can be defined, 1. convection along the surface of vertically oriented membranes and 2. surface potential variations by layer deformations at horizontally oriented membranes. Both effects should affect transport across the layer to the membrane surface and across the membrane. According to the theoretical predictions first experiments with gramicidin channels incorporated into artificial phosphatidylserine bilayer membranes show a significant difference in single channel currents in vertical and horizontal membranes. The complexity of biological membrane functions requires investigation of isolated membrane surface reactions and transport systems to study the gravisensitivity for each process separately.

Cell Membrane↗
PubMed1997

Contractile properties of rat, rhesus monkey, and human type I muscle fibers.

It is well known that skeletal muscle intrinsic maximal shortening velocity is inversely related to species body mass. However, there is uncertainty regarding the relationship between the contractile properties of muscle fibers obtained from commonly studied laboratory animals and those obtained from humans. In this study we determined the contractile properties of single chemically skinned fibers prepared from rat, rhesus monkey, and human soleus and gastrocnemius muscle samples under identical experimental conditions. All fibers used for analysis expressed type I myosin heavy chain as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Allometric coefficients for type I fibers from each muscle indicated that there was little change in peak tension (force/fiber cross-sectional area) across species. In contrast, both soleus and gastrocnemius type I fiber maximal unloaded shortening velocity (Vo), the y-intercept of the force-velocity relationship (Vmax), peak power per unit fiber length, and peak power normalized for fiber length and cross-sectional area were all inversely related to species body mass. The present allometric coefficients for soleus fiber Vo (-0.18) and Vmax (-0.11) are in good agreement with published values for soleus fibers obtained from common laboratory and domesticated mammals. Taken together, these observations suggest that the Vo of slow fibers from quadrupeds and humans scale similarly and can be described by the same quantitative relationships. These findings have implications in the design and interpretation of experiments, especially those that use small laboratory mammals as a model of human muscle function.

Animals↗
PubMed1997

Peak force and maximal shortening velocity of soleus fibers after non-weight-bearing and resistance exercise.

This study examined the effectiveness of resistance exercise as a countermeasure to non-weight-bearing-induced alterations in the absolute peak force, normalized peak force (force/fiber cross-sectional area), peak stiffness, and maximal shortening velocity (Vo) of single permeabilized type I soleus muscle fibers. Adult rats were subjected to the following treatments: normal weight bearing (WB), non-weight bearing (NWB), or NWB with exercise treatments (NWB+Ex). The hindlimbs of the NWB and NWB+Ex rats were suspended for 14 days via tail harnesses. Four times each day, the NWB+Ex rats were removed from suspension and performed 10 climbs (approximately 15 cm each) up a steep grid with a 500-g mass (approximately 1.5 times body mass) attached to their tail harness. NWB was associated with significant reductions in type I fiber diameter, absolute force, normalized force, and stiffness. Exercise treatments during NWB attenuated the decline in fiber diameter and absolute force by almost 60% while maintaining normalized force and stiffness at WB levels. Type I fiber Vo increased by 33% with NWB and remained at this elevated level despite the exercise treatments. We conclude that in comparison to intermittent weight bearing only (J.J. Widrick, J.J. Bangart, M. Karhanek, and R.H. Fitts. J. Appl. Physiol. 80: 981-987, 1996), resistance exercise was more effective in attenuating alterations in type I soleus fiber absolute force, normalized force, and stiffness but was less effective in restoring type I fiber Vo to WB levels.

Animals↗
PubMed1990

Cement line staining in undecalcified thin sections of cortical bone.

A technique for demonstrating cement lines in thin, undecalcified, transverse sections of cortical bone has been developed. Cortical bone samples are processed and embedded undecalcified in methyl methacrylate plastic. After sectioning at 3-5 microns, cross-sections are transferred to a glass slide and flattened for 10 min. Sections of cortical bone are stained for 20 sec free-floating in a fresh solution of 1% toluidine blue dissolved in 0.1% formic acid. The section is dehydrated in t-butyl alcohol, cleared in xylene, and mounted with Eukitt's medium. Reversal lines appear as thin, scalloped, dark blue lines against a light blue matrix, whereas bone formation arrest lines are thicker with a smooth contour. With this technique cellular detail, osteoid differentiation, and fluorochrome labels are retained. Results demonstrate the applicability of a one-step staining method for cement lines which will facilitate the assessment of bone remodeling activity in thin sections of undecalcified cortical bone.

Animals↗
PubMed1995

Review of spaceflight and hindlimb suspension unloading induced sarcomere damage and repair.

Hindlimb suspension unloading (HSU) and spaceflight microgravity induce atrophy of the slow adductor longus muscle fibers which, following reloading, exhibit eccentric contraction (EC)-like lesions (abnormal widening of sarcomeres with A band disruption and excessively wavy, extracted Z lines). These lesions are similar morphologically to those produced in normal muscles after strenuous eccentric exercise. It appears that atrophic muscles exhibit increased susceptibility to eccentric damage because lesions are produced during nonstressful voluntary movements upon return to weightbearing. The EC-like lesions are absent in the unweighted conditions, but appear in HSU rats 15-60 minutes after reloading and in space-flown rates about 4 hrs after landing. By 12 hours, many EC-like lesioned sarcomeres are fully covered by longitudinal patches of Z line-like material which increases in density by 48 hours, producing the so-called "Z line streaming" morphology. In this case, Z line streaming is indicative of rapid repair of damaged sarcomeres rather than the onset of sarcomere breakdown. Immunoelectron microscopy is necessary to determine the composition of this dense material. By 9 days of reloading at 1 gravity, sarcomeres have regained normal structure, except for very rare persistence of faint Z patches. The morphological data indicate that Z patches serve at least two functions: 1) to permit contractile force to be transmitted across the damaged sarcomeres and 2) to provide a scaffold upon which sarcomeres are reconstructed in an active functional muscle.

Animals↗