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Query: UMLS:C0344329 (collapse)
 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Acute lung disease is commonly associated with interstitial pulmonary edema and a tendency towards partial or total alveolar collapse. To counteract this tendency mechanical ventilation is successfully used in most cases. Mechanical ventilation, however, leads to a harmful retention of water and salt, which may worsen interstitial pulmonary edema and further impair gas exchange. This problem seems to be less known. A survey of the effects of currently used modes of mechanical ventilation on excretory function and hemodynamics of the kidneys is given together with a short review of the possible afferent and efferent mechanisms which mediate the renal response to mechanical ventilation. Some clinical suggestions are made to break through the vicious cycle between mechanical ventilation and kidney function.
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PMID:[Artificial respiration and kidney function disorder--a vicious circle?]. 389 Jun 7

A stable ecosystem resists large, rapid changes in the sizes of its constituent populations which upset the orderly flow of energy and nutrients. An early example of such alteration was the conversion to desert of the rich Tigris and Euphrates valleys through erosion and salt accumulation resulting from faulty irrigation practices that caused the downfall of the great Mesopotamian civilization. Overgrazing and poor cultivation practices have contributed over the millennia to the expansion of the Sahara Desert. Attempts to cultivate too intensively the fragile soil of tropical rainforest areas are suspected of being in part responsible for the collapse of the Mayan civilization. The 19th century Irish potato famine because of heavy reliance of the Irish population on a single, highly productive crop led to 1.5 million deaths when the potato monoculture, a simple agricultural ecosystem, fell victim to a fungus. Modern agriculture's desire to maximize yields per acre are worrisome ecologically (increases in the use of pesticides and inorganic fertilizers). The liabilities include that as larger land areas are farmed the tracts available for reservoirs of species diversity and for natural ecosystems become smaller. Pressure to expand agriculture to steep hillsides unsuitable for cultivation has led to serious erosion in Indonesia, and increasing slash-and-burn practices are destroying tropical forests in the Philippines. The enormous expansion of wheat or rice monoculture has increased the probability of epidemic crop failure from insects or disease. 37% of the world's population is under 15 years of age which means that population will grow for 50-70 years more before leveling off. Despite a declining growth rate population would still increase 30% or more during the transition to stability. Zero global population growth is required for a prosperous and environmentally sustainable civilization.
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PMID:Human population and the global environment. 483 78

Monolayer techniques were used to study the interactions of various lipids (cholesterol, lysophosphatidyl choline, phosphatidal ethanolamine, phosphatidyl choline, sphingomyelin, stearic acid, and lipids extracted from plasma high density lipoproteins and very low density lipoprotein) with the lipid-free protein subunit of rat plasma high density lipoprotein and with rat plasma albumin. The proteins were injected under the lipid monolayer at fixed area, and the increase in surface pressure (decrease in surface tension) was measured as a function of time. With all lipids, both the rate and magnitude of this increase were greater with the apolipoprotein than with albumin. The degree of film penetration of pure lipid films (at an initial film pressure of 15 dynes/cm) by the two proteins followed the same order: cholesterol > phosphatidal ethanolamine > phosphatidyl choline > stearic acid > sphingomyelin > lysophosphatidyl choline. Other variables studied were protein concentration, initial film pressure, and pH. Two distinctive properties of the apolipoprotein were the penetration of lipid films at pressures above the collapse pressure of the protein, and the formation of a film even at low salt concentration. High surface activity and strong interaction of HDL-protein with lipid monolayers may be associated with the flexibility of the protein molecule due to absence of disulfide bridges. The unusual surface activity of HDL-protein may be intimately related to the mechanism of formation of the lipoprotein.
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PMID:Lipid monolayers: interactions with the apoprotein of high density plasma lipoprotein. 572 15

The quick-freeze, deep-etch, rotary-replication technique is useful for visualizing cells and cell fractions but does not work with suspensions of macromolecules. These inevitably clump or collapse during deep-etching, presumably due to surface tension forces that develop during their transfer from ice to vacuum. Previous protocols have attempted to overcome such forces by attaching macromolecules to freshly cleaved mica before drying and replication. I describe here an adaptation of this procedure to the deep-etch technique as otherwise practiced. My innovation is to mix the molecules with an aqueous suspension of tiny flakes of mica and then to quick-freeze and freeze-fracture the suspension exactly as if one were dealing with cells. The fracture inevitably strikes the surfaces of many mica flakes and thereby cleaves the adsorbed macromolecules cleanly enough to reveal interesting substructure within them. The subsequent step of deep-etching exposes large expanses of unfractured mica and thus reveals intact macromolecules. These macromolecules are not obscured by salt deposits, even if they were frozen in hypertonic solutions, apparently because the fracturing step removes nearly all of the overlying electrolyte. Moreover, these macromolecules are minimally freeze-dried (since exposure is sufficient after only 3 min of etching at -102 degrees C) so they retain their three-dimensional topology. I show that molluscan hemocyanin is a good internal standard for this new technique. It is available commercially in stable solutions, mixes well with all sizes of macromolecules, and consists of particles that display distinct five-start surface helices, which have been measured carefully in the past and which possess a known handedness, useful for determining the orientation of micrographs when examining the various helical patterns possessed by most types of extended macromolecules. The fractured hemocyanin particles also display characteristic internal structures, which permit determination of the elevation of the "molecular cleavage" described above. Finally, molluscan hemocyanin is delicate enough to reflect bad freezing or poor replication, if these steps become a problem. A survey of several macromolecules is presented, including soluble enzymes, antibodies, filamentous proteins and nucleoproteins. These images, for the most part, correspond to those previously obtained by negative staining. New details of their structures are noted, and the images are used to illustrate both the advantages and drawbacks of the new procedure.
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PMID:Procedure for freeze-drying molecules adsorbed to mica flakes. 668 95

Thirty pregnant beef cows were utilized to determine the effects of winter Mg supplementation regimen on blood minerals after cows were turned to a spring tetanigenic tall fescue pasture. The winter Mg treatments were (1) tall fescue hay with free access to a Mg-deficient salt-mineral mix, (2) 6.4 kg of corn silage dry matter plus 114 g MgO/d and (3) tall fescue hay with free access to a salt-mineral mix containing 40% MgO from January 1 to February 15. All cows were then placed on the same tetanigenic pasture from February 15 to April 17 with free access to a Mg-deficient salt-mineral supplement. Forage Mg remained below .2% during the experiment. Forage Ca, P and Al changed throughout the spring, attaining maximum values of .35%, .46% and 415 ppm, respectively. Forage N and K also increased throughout the spring, reaching values of 3.5 and 3.8%, respectively, at the April 3 sampling. The forage K:(Ca + Mg) ratio approached 2.2 by March 26, which coincided closely with the average tetany date (March 29). Serum Mg averaged 1.97, 3.58 and 2.06 mg/dl for treatments 1, 2 and 3, respectively, on February 15 before turning cows to pasture. There were no treatment differences for serum Ca, P and K during the experiment. Eight cows exhibited symptoms of grass tetany (collapse) on an average date of March 29. Winter Mg supplementation provided little long-term protection against hypomagnesemia after turning cows to tetanigenic pasture, indicating that cows must have a supplemental source of Mg during this critical period.
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PMID:Labile magnesium reserves in beef cows subjected to different prepasture supplementation regimens. 674 52

When spread from organic solvents onto electrolyte solutions, the Ca2+ ionophores A23187 (I) and X537A (II) formed films with relatively high surface pressures potentials. Ionophores I had collapse pressures between 16 and 19 dynes/cm and nearly equal surface activity on distilled water and on 1000 mEq of either sodium chloride or calcium chloride. Film pressure did not reveal appreciable ion selectivity. However, the surface potential of I on calcium chloride solution was higher than that on sodium chloride, and the potential difference, delta(deltaV), of 40 mv was independent of the electrolyte concentration. In contrast, the ion selectivity of II was dependent on the electrolyte concentrations since the delta(deltaV) value between calcium chloride and sodium chloride was maximal (130 mv) on 1000 mEq and negligible on 500- and 2000-mEq salt solutions. The isotherms of phospholipid-ionophore films were markedly different from those of the individual components, although they revealed ionophore characteristics at low film pressures and phospholipid behavior at high film pressures. The magnitude of the surface potential indicated that dipalmitoyl phosphatidylcholine enhanced, whereas mitochondrial lipid and cardiolipin reduced, the preference of the two ionophores for Ca2+ over Na+. Since the ion selectivity was manifested most at both high electrolyte and high lecithin concentrations, the ionophore probably prefers the low dielectric constant of neutral lipid membranes to complex with the selected cation.
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PMID:Surface properties of membrane systems: interaction of electrolyte and lipid with Ca2+ ionophores. 676 74

Electron microscopy of HeLa metaphase nucleoids (i.e. whole metaphase cells exposed to 2 M salt and non-ionic detergent) spread by the Kleinschmidt technique, reveals a variety of protein-depleted structures (spreads) derived from chromosomes. Spreads vary in size and shape. At one extreme are oval structures with one or more cores surrounded by a network of supercoiled fibres. These fibres are probably arranged as loops and we estimate that 600-1000 may emerge from a single, large core region. At the other extreme are chromosome-shaped spreads with an elongated core which takes the form of a multifibred axis. At intervals groups of lateral fibres appear to emerge from each axis to produce the network. Spreads intermediate between these extremes occur in which axial fibres can be resolved in only part of the elongated core. Similar structures are observed in chromosomes deproteinized and spread after isolation by a procedure which preserves high molecular weight DNA. The appearance of chromosomes isolated by the Wray-Stubblefield hexylene glycol procedure agrees in general with previous findings of others, except that in some more extended spreads axial fibres are visible. We believe our observations are consistent with the idea that the chromonema of each metaphase chromatid contains regions of multistranded DNA. We do not propose, however, that the chromatid is functionally multineme, but rather that axial fibre folding either within or between chromomere regions contributes to packing of DNA in the metaphase chromosome. These regions of constraint re also postulated as the locations of emergence of lateral loops. In spread preparations the axial fibres are seen clearly only when chromatids have been elongated beyond the contracted metaphase length. Elongation would be produced both by relaxation of chromosomal coils (gyres) and by extension of the chromonema upon deproteinization and spreading. Whereas in deproteinized nucleoids the long axis is liable to elongate, fragment or collapse, the chromomena of Wray-Stubblefield chromosomes is locked at the metaphase (gyred) length and axial fibres are generally not visible. We propose that the assembly of the complex DNA axis of the metaphase chromosome from its extended interphase counterpart plays a major part in increasing the DNA packing ratio in the mitotic cell.
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PMID:Packing DNA into chromosomes. 722 16

The bile salts chenodeoxycholate (CDC) and its 7 beta-hydroxy epimer ursodeoxycholate (UDC) are administered therapeutically (as acids) to dissolve cholesterol gallstones in man. Since their micellarr solutions and those of their physiological conjugates differ strikingly in their capacities to solubilize cholesterol, we studied the interfacial and micellar properties of the epimers by a number of complimentary physical--chemical methods and correlated these with their solubilizing capacities. The critical micella concentrations (cmc) estimated by surface tension, dye titration, and turbidimetry were similar (1-5 mM), varying slightly with the bile salt species, the method employed, NaCl concentration (0-1 M), and temperature (10-50 degrees C). The weight-average aggregation number (number of monomers per micelle, nw) at the cmc, derived from Debye plots of conventional light-scattering data and from the mean hydrodynamic radii of the micelles obtained by quasi-elastic light-scattering spectroscopy, revealed no appreciable differences between the UDC-CDC epimers or between their conjugates. From the mean hydrodynamic radii, the taurine conjugates were found to form larger micelles (nw = 15-17) than the glycine conjugates (nw = 13) which in turn were larger than the free species (n w = 5), respectively. Consistent with previous experimental deductions, free and conjugated CDC micelles grew slightly in size with increases in total lipid concentration, but UDC micelles did not. With solubilization of cholesterol monohydrate, the mean sizes of UDC (13.4 A) and of CDC (13 A) micelles in 10 g/dL solutions did not change appreciably, even as the cholesterol saturation limit was reached. At the air-5 M NaCl (pH 2) interface, the glycine conjugates formed more expanded monomolecular films than the free acid, and both UDC and its glycine conjugate collapsed at surface pressures that were 10-20 mN m-1 lower than the collapse pressures of monolayers of CDC and its glycine conjugate. Similarly, adsorbed monolayers of ionized UDC and its taurine conjugate lowered the surface tension of water approximately 5 mN m-1 less than equimolar concentrations of CDC and its taurine conjugate. By employing high-performance reversed-phase liquid chromatography (HPLC), we measured the relative hydrophilic--hydrophobic properties of the bile salts and found a close correlation between HPLC mobility and cholesterol-solubilizing cpacity. Assuming a single cholesterol binding site per micelle, we estimated from the nw values and bile salt/cholesterol saturation ratios that the magnitude of the cholesterol binding constant (K) was 5.7 X 10(6) L/mol for unconjugated CDC and 2.5 X 10(5) L/mol for unconjugated UDC at 30 degrees C. These results suggest that the differences in cholesterol-solubilizing capacities of CDC and UDC and their conjugates are due to subtle differences in micellar structure, resulting from the axial or equatorial orientation of the 7-hydroxyl function and the various conjugating groups...
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PMID:Thermodynamic and molecular basis for dissimilar cholesterol-solubilizing capacities by micellar solutions of bile salts: cases of sodium chenodeoxycholate and sodium ursodeoxycholate and their glycine and taurine conjugates. 726 61

FK506 can show efficacy in transplant rejection even after other immunosuppressive drugs have been ineffective. However, the lack of a suitable animal model has hindered the study of FK nephrotoxicity, which has been noted as a common adverse effect in human trials. In this paper, we report a model of chronic FK nephrotoxicity in which renal structure and function are worsened by sodium depletion. Pair-fed male Sprague-Dawley rats were given FK (6 mg/kg p.o.) or vehicle for 21 days on a low-salt or normal diet. There was no significant difference in body weight between FK and vehicle groups. The FK whole-blood trough levels (3-10 ng/ml) in rats are similar to those in FK treated transplant patients. In sodium-depleted rats, FK clearly decreased GFR (0.09 +/- 0.03 ml/min/100 g vs. 0.94 +/- 0.06 ml/min/100 g in the vehicle group, P < 0.01), urinary osmolarity (UOsm, P < 0.01) and plasma magnesium (P < 0.01) and increased plasma creatinine (Pcr, P < 0.01), fractional excretion of magnesium (P < 0.01), urine volume (P < 0.01), plasma renin activity (PRA, P < 0.05), and alanine aminopeptidase (AAP, P < 0.05) as compared with those in the vehicle group. Salt depletion significantly potentiated these functional changes as compared with those in the normal salt group (GFR, UOsm, Pcr, PRA, and AAP of the low salt group vs. those of the normal salt group, P < 0.05 by ANOVA). In the sodium-depleted rats, the main lesion in the rat kidneys was focal collapse and vacuolization in proximal tubules, but there was also significant interstitial fibrosis. In contrast, no injury was observed in the sodium-replete rat kidneys. In conclusion, an experimental model of FK nephrotoxicity in sodium-depleted rats has been developed that is characterized by reduced GFR and structural damage to the proximal tubule accompanied by interstitial fibrosis. Sodium depletion appears to potentiate these changes at blood levels similar to those achieved in patients receiving FK.
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PMID:Enhancement of FK506 nephrotoxicity by sodium depletion in an experimental rat model. 750 14

We present a detailed computational study of the influence of salt on the configurations, energies, and dynamics of supercoiled DNA. A potential function that includes both elastic and electrostatic energy components is employed. Specifically, the electrostatic term, with salt-dependent coefficients, is modeled after Stigter's pioneering work on the effective diameter of DNA as a function of salt concentration. Because an effective charge per unit length is used, the electrostatic formulation does not require explicit modeling of phosphates and can be used to study long DNAs at any desired resolution of charge. With explicit consideration of the electrostatic energy, an elastic bending constant corresponding to the nonelectrostatic part of the bending contribution to the persistence length is used. We show, for a series of salt concentrations ranging from 0.005 to 1.0 M sodium, how configurations and energies of supercoiled DNA (1000 and 3000 base pairs) change dramatically with the simulated salt environment. At high salt, the DNA adopts highly compact and bent interwound states, with the bending energy dominating over the other components, and the electrostatic energy playing a minor role in comparison to the bending and twisting terms. At low salt, the DNA supercoils are much more open and loosely interwound, and the electrostatic components are dominant. Over the range of three decades of salt examined, the electrostatic energy changes by a factor of 10. The buckling transition between the circle and figure-8 is highly sensitive to salt concentration: this transition is delayed as salt concentration decreases, with a particularly sharp increase below 0.1 M. For example, for a bending-to-twisting force constant ratio of A/C = 1.5, the linking number difference (delta LK) corresponding to equal energies for the circle and figure-8 increases from 2.1 to 3.25 as salt decreases from 1.0 to 0.005 M. We also present in detail a family of three-lobed supercoiled DNA configurations that are predicted by elasticity theory to be stable at low delta Lk. To our knowledge, such three-dimensional structures have not been previously presented in connection with DNA supercoiling. These branched forms have a higher bending energy than the corresponding interwound configurations at the same delta Lk but, especially at low salt, this bending energy difference is relatively small in comparison with the total energy, which is dominated by the electrostatic contributions. Significantly, the electrostatic energies of the three-lobed and (straight) interwound forms are comparable at each salt environment. We show how the three-lobed configurations change slowly with ALk, resulting in branched interwound forms at higher salt. In longer chains, the branched forms are highly interwound, with bent arms. At low salt, the branched supercoils are asymmetric, with a longer interwound stem and two shorter arms. From molecular dynamics simulations we observe differences in the motions of the DNA as a function of salt. At high salt, the supercoiled chain is quite compact but fairly rigid, whereas at low salt the DNA is loosely coiled but more dynamic. Especially notable at low salt are the large-scale opening and closing of the chain as a whole and the rapid "slithering"of individual residues past one another. Toroidal forms are not detected under these conditions. However, the overall features of the open, loose supercoils found at low salt are more similar to those of toroidal than interwound configurations. Indeed,simulated x-ray scattering profiles reveal the same trends observed experimentally and are consistent with a change from closed to open forms as salt is decreased. Like the minimization studies, the dynamics reveal a critical point near 0.1 M associated with the collapse of loose to tight supercoils. Near this physiological concentration, enhanced flexibility of the DNA is noted. The collective observations suggest a potential regulatory role for salt on supercoiled DNA function, not only for closed circular DNA,but also for linear DNA with small looped regions.
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PMID:The influence of salt on the structure and energetics of supercoiled DNA. 769 59


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