Function Of Osmotic Pressure Research Articles

Isothermal calorimetry studies of DNA condensation under osmotic pressure.

The physics behind DNA condensation has been a subject of research for many years. Despite this, the exact mechanism under the condensed process is still not fully understood. Isothermal calorimetry introduces a unique perspective by providing the full thermodynamics parameter that drives the condensation process. Here we report on isothermal calorimetry studies of DNA condensation by trivalent ions. We investigate this process while altering the osmotic pressure through the addition of polyethylene glycol. We use a home-built Python script to fit the two-peek signal and obtain the full thermodynamics parameter. We find a shift in the condensation peak as a function of osmotic pressure indicating osmotic pressure enhances condensation. These results are key to understanding the basic process of DNA condensation and specifically with the surrounding by osmotic pressure.

Electromagnetic Radiation Influences on Rheological Parameters of Rats’ Blood

The present work aimed to study the alterations in blood viscoelasticity and hematological parameters as a result of the exposure to electric field (50 Hz-4 kV/m-8h/d), magnetic field (50 Hz -0.3 mT-8h/d) and high energy photon (6 MeV; 0.002Ao-1 rad). The blood tissue was chosen as biomarker for the direct and delay exposure evaluations whereas its viscosity coefficient as function of shear rate was monitored and its mechanical characteristics as function of osmotic pressure was measured. In addition, the hematological parameters were observed for all collected blood samples and correlated to the blood viscoelasticity. The obtained results showed remarkable effects on the studied blood parameters even at short exposure periods and /or after delayed exposure effects. From the present results it may be concluded that the exposure to electric and magnetic field at extremely low frequency range has hazardous effect not less than the ionizing radiation at very low dose. Our findings indicated that maximum deteriorative effects resulted due to exposure to magnetic field (30 days) whereas the blood viscosity coefficient, RBCs elastic limit, and hemoglobin were decreased relative to the control by -38%, -30% and -25% respectively. Moreover, the changes in blood viscoelasticity and hematological parameters as a result of the exposure even after 45 days’ post exposure support the hazardous effects of such fields. The need of new recommendations for exposure to such fields and frequent blood checkup should be done from time to another specially for residents who expose for long times.

Nuclei deformation reveals pressure distributions in 3D cell clusters.

Measuring pressures within complex multi-cellular environments is critical for studying mechanobiology as these forces trigger diverse biological responses, however, these studies are difficult as a deeply embedded yet well-calibrated probe is required. In this manuscript, we use endogenous cell nuclei as pressure sensors by introducing a fluorescent protein localized to the nucleus and confocal microscopy to measure the individual nuclear volumes in 3D multi-cellular aggregates. We calibrate this measurement of nuclear volume to pressure by quantifying the nuclear volume change as a function of osmotic pressure in isolated 2D culture. Using this technique, we find that in multicellular structures, the nuclear compressive mechanical stresses are on the order of MPa, increase with cell number in the cluster, and that the distribution of stresses is homogenous in spherical cell clusters, but highly asymmetric in oblong clusters. This approach may facilitate quantitative mechanical measurements in complex and extended biological structures both in vitro and in vivo.

Driving a planar model system into the 3(rd) dimension: generation and control of curved pore-spanning membrane arrays.

The generation of a regular array of micrometre-sized pore-spanning membranes that protrude from the underlying surface as a function of osmotic pressure is reported. Giant unilamellar vesicles are spread onto non-functionalized Si/SiO(2) substrates containing a highly ordered array of cavities with pore diameters of 850 nm, an interpore distance of 4 μm and a pore depth of 10 μm. The shape of the resulting pore-spanning membranes is controlled by applying an osmotic pressure difference between the bulk solution and the femtoliter-sized cavity underneath each membrane. By applying Young-Laplace's law assuming moderate lateral membrane tensions, the response of the membranes to the osmotic pressure difference can be theoretically well described. Protruded pore-spanning membranes containing the receptor lipid PIP(2) specifically bind the ENTH domain of epsin resulting in an enlargement of the protrusions and disappearance as a result of ENTH-domain induced defects in the membranes. These results are discussed in the context of an ENTH-domain induced reduction of lateral membrane tension and formation of defects as a result of helix insertion of the protein in the bilayer.

Design and Characterization of an Osmotic Sensor for the Detection of Events Associated with Dehydration and Overhydration.

The level of hydration in the human body is carefully adjusted to control the electrolyte balance that governs the biochemical processes that sustain life. An electrolyte deficiency caused by de- or overhydration will not only limit human performance, but can also lead to serious health problems and death if left untreated. Because humans can withstand a change in hydration of only n}{}{pm}{20%}, frequent monitoring should be performed in risk groups. This paper presents an osmotic hydration sensor that can record the level of hydration as a function of osmotic pressure in phosphate buffered saline or sodium-chloride solutions that simulate the interstitial fluid in the body. The osmotic pressure is recorded with the aid of an ion-exchange membrane that facilitates the migration of water and cations, in favor of reverse osmosis or gas separation membranes. The hydration sensor is designed to be coupled to an inductively powered readout circuit designed for integration in a micro-implant that has previously been shown to consume only 76 n}{}mu{rm W} of power. The dynamic range spans a state of serious overhydration (220 n}{}{rm mOsm} {rm L}^{-1}) to a serious state of dehydration (340 n}{}{rm mOsm} {rm L}^{-1}) with a response time of n}{}{sim}{rm 7} {rm h} (for a variation of hydration of 20%).

Bulk modulus of poly(N-isopropylacrylamide) microgels through the swelling transition

We report measurements of the bulk modulus of individual poly(N-isopropylacrylamide) microgels along their swelling transition. The modulus is determined by measuring the volume deformation of the microgel as a function of osmotic pressure using dextran solutions. We find that the modulus softens through the transition, displaying a nonmonotonous behavior with temperature. This feature is correctly reproduced by the theory of Flory for polymer gels, once the concentration dependence of the solvency parameter is properly incorporated.

DNA Cholesteric Pitch as a Function of Density and Ionic Strength

The nature of chiral interactions among chiral biopolymers, such as DNA, protein α-helices, and rodlike virus particles, remains elusive. In particular, a satisfactory model connecting molecular chiral interactions and the pitch of the resulting chiral mesophases is lacking. We report the measurement of short-fragment (146-bp) DNA cholesteric spherulite pitch as a function of osmotic pressure, average DNA interaxial spacing, and salt concentration. We determined cholesteric pitch and interaxial spacing by polarizing optical microscopy and x-ray scattering, respectively, from which the twist-angle between DNA molecules can be calculated. Surprisingly, we found that decreasing ionic strength resulted in weaker chiral interactions between DNA chains, as evidenced by the decrease in the twist-angle, and consequent increase in the cholesteric pitch, for a fixed interaxial spacing. We propose that this behavior can be explained by increased smearing-out of the helical charge pattern along DNA as the Debye screening length is increased.

Phase transitions as a function of osmotic pressure in Saccharomyces cerevisiae whole cells, membrane extracts and phospholipid mixtures

Fourier Transform Infrared spectroscopy (FTIR) was used to determine the phase transition temperature of whole Saccharomyces cerevisiae W303-1 A cells as a function of Aw in binary water–glycerol media. A phase transition occurred at 12 °C in water, at 16.5 °C at Aw=0.75, and at 19.5 °C at Aw=0.65. The temperature ranges over which transition occurred increased with decreasing Aw. A total lipid extract of the plasma membranes isolated from S. cerevisiae cells was also studied, with a phase transition temperature determined at 20 °C in pure water and at 27 °C in binary water–glycerol solutions for both Aw levels tested. The pure phospholipids dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) and three binary mixtures of these phospholipids (percentage molar mixtures of DMPC/DMPE of 90.5/9.5, 74.8/25.2, and 39.7/60.3) were studied. For DMPC, there was no influence of Aw on the phase transition temperature (always 23 °C). On the other hand, the phase transition temperature of DMPE increased with decreasing Aw for the three aqueous solutions tested (glycerol, sorbitol and sucrose), from 48 °C in water, to 64 °C for a solution at Aw=0.67. For the DMPC/DMPE mixtures, transitions were found intermediate between those of the two phospholipids, and a cooperative state was observed between species at the gel and at the fluid phases.

Compared tolerance to osmotic stress in various microorganisms: Towards a survival prediction test

The osmotic tolerance of microbial cells of different microorganisms was investigated as a function of glycerol concentration and temperatures. Cells displayed specific sensitivity to dehydration in glycerol solutions. The viability of Gram-negative strains (Escherichia coli, Bradyrhizobium japonicum), Gram-positive strains (Lactobacillus plantarum, L. bulgaricus), and yeasts (Saccharomyces cerevisiae, Candida utilis) decreased with increasing osmotic pressure. For each strain, a characteristic osmotic pressure threshold causing a loss of 40% of the population at the growth temperature was determined: 26-40 MPa for E. coli, 15-25 MPa for B. japonicum, 7-15 MPa for L. bulgaricus, 40-133 MPa for L. plantarum, 50-100 MPa for S. cerevisiae, and 15-26 MPa for C. utilis. Because this threshold varies with temperature, it was possible to construct a diagram that could be helpful to the determination of the sensitivity of each strain to osmotic stress as a function of osmotic pressure and temperature.

Cubatic liquid-crystalline behavior in a system of hard cuboids.

The lyotropic phase behavior of cuboidal particles was investigated via Monte Carlo simulations. Hard cubes were approximated by suitably shaped clusters of hard spheres. Changes in concentration and structure of the system were monitored as a function of osmotic pressure P* (imposed in an isobaric ensemble). As expected, an isotropic phase prevailed at low concentrations (low P*) and a crystalline phase formed at high concentrations (high P*). A third distinct phase was also observed for an intermediate range of concentrations (approximately marked by breaks in the P* versus concentration curve). The structure of this mesophase was characterized both visually and analytically by calculating radial distribution functions and order parameters. It was found that such a mesophase exhibits orientational ordering along three axes (cubatic order) but significant translational disorder, thus having a structure clearly distinct from both isotropic and crystalline phases.

Soft matter under osmotic stress

In this article, we will show that the osmotic stress method can be successfully applied to study the thermodynamics of self-assembly phenomena in soft matter systems, such as biopolymer liquid crystals, surfactant and lipid mesophases, and polyelectrolyte–surfactant complexes. We will give two examples to that effect. Firstly, we will present intercolumnar force measurements between cylindrical surfactant micelles in solid-state polyelectrolyte–surfactant complexes as a function of ionic strength. Secondly, we will present measurements of the DNA cholesteric spherulite structure and pitch as a function of osmotic pressure in an effort to evaluate the chiral contribution to the interaction between DNA molecules.

Effects of COR6.6 and COR15am Polypeptides Encoded by COR (Cold-Regulated) Genes of Arabidopsis thaliana on Dehydration-Induced Phase Transitions of Phospholipid Membranes

Cold acclimation of Arabidopsis thaliana includes the expression of cold-regulated (COR) genes and the accumulation of COR polypeptides. The hydration characteristics of two COR polypeptides, COR6.6 and COR15am, have been determined and their effects on the dehydration-induced liquid crystalline-to-gel and lamellar-to-hexagonal II phase transitions in phospholipid mixtures have been examined. After dehydration at osmotic pressures between 8 and 150 MPa, the water content of the COR polypeptides was less than that of bovine serum albumin, with COr15am the least hydrated: bovine serum albumin > COR6.6 > COR15am. Neither COR6.6 nor COR15am altered the dehydration-induced gel lamellar --> fluid lamellar phase transition temperature of either dipalmitoylphosphatidylcholine or dioleoylphosphatidylcholine (DOPC). In multilamellar vesicles of dioleoylphosphatidylethanolamine:DOPC (1:1, mol:mol) prepared by either freeze-thaw or reverse-phase evaporation methods, neither COR6.6, COR15am, nor bovine serum albumin altered the incidence of the dehydration-induced formation of the inverted hexagonal phase as a function of osmotic pressure. However, a specific ultrastructural alteration--the formation of a striated surface morphology in the lamellar domains--was observed in mixtures of dioleoylphosphatidylethanolamine:DOPC that were dehydrated in the presence of COR15am. Nevertheless, neither COR6.6 nor COR15am appears to participate in a specific protein-phospholipid interaction that alters the dehydration-induced phase behavior of phospholipid vesicles.

A critical role of protein-bound water in the catalytic cycle of cytochrome P-450 camphor

The rates of NADH oxidation during the hydroxylation of camphor by cytochrome P-450 cam were followed in the presence of co-solvents used to increase the osmotic pressure surrounding the protein-bound water. As a result, the measured V max decreases independently of the perturbant tested. Roughly 28 molecules of water, involved during the catalytic cycle, are deduced from the variation of V max as a function of osmotic pressure. These molecules, in part, could be those present in the cytochrome P.450 cam-putidaredoxin interface.

Energetics of a hexagonal-lamellar-hexagonal-phase transition sequence in dioleoylphosphatidylethanolamine membranes.

The phase diagram of DOPE/water dispersions was investigated by NMR and X-ray diffraction in the water concentration range from 2 to 20 water molecules per lipid and in the temperature range from -5 to +50 degrees C. At temperatures above 22 degrees C, the dispersions form an inverse (HII) phase at all water concentrations. Below 25 degrees C, an HII phase occurs at high water concentrations, an L alpha phase is formed at intermediate water concentrations, and finally the system switches back to an HII phase at low water concentrations. The enthalpy of the L alpha-HII-phase transition is +0.3 kcal/mol as measured by differential scanning calorimetry. Using 31P and 2H NMR and X-ray diffraction, we measured the trapped water volumes in HII and L alpha phases as a function of osmotic pressure. The change of the HII-phase free energy as a function of hydration was calculated by integrating the osmotic pressure vs trapped water volume curve. The phase diagram calculated on the basis of the known enthalpy of transition and the osmotic pressure vs water volume curves is in good agreement with the measured one. The HII-L alpha-HII double-phase transition at temperatures below 22 degrees C can be shown to be a consequence of (i) the greater degree of hydration of the HII phase in excess water and (ii) the relative sensitivities with which the lamellar and hexagonal phases dehydrate with increasing osmotic pressure. These results demonstrate the usefulness of osmotic stress measurements to understand lipid-phase diagrams.

The density and free water of cholinergic synaptic vesicles as a function of osmotic pressure

Synaptic vesicles from the cholinergic electromotor nerve terminals of Torpedo marmorata are among the most uniform subcellular organelles known and are osmotically sensitive. Changes in density accompanying osmotic perturbation have enabled changes in water content to be calculated; when reffered to a standard state of known volume and water content, fractional and absolute water contents could be calculated for the perturbed states and compared with the fractional free water content as measured by the glycerol space. Under hyperosmotic conditions, discrepancies were found between these two estimates, the glycerol space falling more rapidly than the water space predicted from the density change. This is attributed to a failure of glycerol to displace water imbibed by the membrane as it collapses round an aqueous core of decreasing volume. ‘Reserve’ vesicles obeyed a relationship between density, osmotic load and osmolality derived for a perfect osmometer, and independent estimates of fractional free water content under standard conditions and osmotic load were made. The former of these agreed well with the glycerol space under standard conditions and the latter agreed with previous estimates of the osmotic load using morphological and analytical data and an assumed activity coefficient of 0.65. Finally, it was possible to model the interconversion of reserve and recycling vesicles more accurately than in previous work.

Phase separations induced in aqueous colloidal suspensions by dissolved polymer

Several experimental studies have demonstrated the tendency of non-adsorbing dissolved polymer to cause a phase separation in otherwise homogeneous colloidal suspensions. This separation occurs with hard-sphere systems as well as those stabilized either sterically or electrostatically. A restabilization at higher polymer concentrations has been observed in some electrostatically and sterically stabilized dispersions.A theory based on statistical mechanics presented here predicts such phase transitions in aqueous colloidal suspensions. The effective interaction potential between two colloidal particles comprises as combination of the volume restriction potential of Asakura and Oosawa and the classical electrostatic repulsion of Derjaguin. The free energy is calculated via second-order perturbation theory with an effective hard-sphere system serving as the reference state. A fluid–solid phase diagram emerges showing the volume fraction of particles in each phase as a function of osmotic pressure. The details of the phase behaviour depend on the polymer concentration and molecular weight, the ionic strength and the electrostatic potential and size of the particles. At high polymer concentrations, a semi-dilute theory of Muthukumar and Edwards is employed to account for the decreasing range of polymer-polymer and polymer-particle interactions with increasing concentration. This behaviour provides a mechanism for electrostatic restabilization at sufficient polymer concentrations.The results for the polymer concentration required for destabilization, cF, agree well with experimental observations of Sperry, Hopfenberg and Thomas. Corresponding measurements of the densities of the resulting phases have not been reported. The predictions of restabilization also remain to be tested quantitatively, but the results conform qualitatively with experimental observation.

Core structure, internal osmotic pressure and irreversible structural changes of chromaffin granules during osmometer behaviour

In the adrenal medullary cells, catecholamines are stored in and secreted from specialized secretory vesicles, the chromaffin granules. In order to gain some understanding of both functions of chromaffin granules, it is important to characterize their biophysical organization. Using isolated bovine chromaffin granules we have investigated the osmometer behaviour of chromaffin granules by 31P-NMR and fluorescence spectroscopy, by turbidity measurements and by electron-microscopic determination of chromaffin granule size distributions. On the basis of the osmometer model we have formulated equations predicting the behaviour of the native catecholamine fluorescence quenching and of the size of chromaffin granules as a function of osmolarity and have shown experimentally that the granules' behaviour conforms to these. It was possible to estimate the osmotic activity of the chromaffin granule core solution and the mean absolute water space in chromaffin granules from the determination of the size distributions as a function of osmotic pressure. With NMR spectroscopy a selective line-broadening of the α- and β-resonances was observed with increasing osmolarities, while the γ-phosphorus resonances remained virtually unchanged. Possibly there is an increase in core viscosity with osmolarity which affects only the α- and β-phosphorus groups. While suspending chromaffin granules from lower to higher osmolarities causes no lysis, moving them back to their original osmolarity at which they were previously stable lyses them, thereby releasing a maximum of 70% of their releasable protein. This ‘hyperosmolar’ lysis is independent of preincubation times in the higher osmolarities and of the absolute dilution applied but depends on dilution beyond the 405 to 322 mosM sucrose range. Under the experimental conditions no uptake of sucrose from the medium into the granules could be measured, thereby suggesting that hyperosmolar lysis is a phenomenon not due to solute penetration. Since with NMR and fluorescence spectroscopy no chemical changes in the core composition can be observed, we conclude that hyperosmolar lysis may be caused by irreversible membrane relaxation upon osmotic shrinking.

Effect of osmotic pressure, Na+-K+ ratio and medium concentration on the enzyme activity and growth of L cells in suspension culture.

The effect of changes in osmotic pressure and in the Na+/K+ ratio on the doubling time, maximum cell population, enzyme activity, and isoenzyme distribution pattern in suspension cultures of L cells was determined. The growth of viable cells is relatively flat over a rather wide range of osmotic pressures (220 to 440 mOsm per kg). The presence of extra salt or sucrose beyond that needed to reach the minimum osmotic pressure (220) is detrimental to cell growth as reflected by a delay in the onset of logarithmic growth, a slower growth rate, a decreased maximum population, and accelerated death phase. Excessive K+ ion is toxic, but the level at which it is toxic interacts with osmotic pressure of the medium. Enzyme activity and isoenzyme distribution patterns for those enzymes studied did not vary as a function of osmotic pressure, ionic ratios, or medium concentration.

An analysis of irreversible plant cell elongation

A model for plant cell elongation has been developed from rate equations for osmotic uptake of water and irreversible expansion of the cell wall. Assuming elastic equilibrium and a linear viscoelastic wall, cell elongation rate is derived as a function of osmotic pressure, “extensibility” of the wall, water permeability and cell size. The derived formulations predict growth curves comparable to those observed experimentally. Certain consequences of the derived formulations are discussed. It is shown that the turgor pressure of a growing cell will always be less than the water potential of the cell. This difference may be infinitesimal or finite, depending on the values of the physical parameters of the cell. It is also shown that at positive turgor pressures water must always move from a mature cell to a growing cell.

XII. The function of osmotic pressure in the analogy between solutions and gases

(1888). XII. The function of osmotic pressure in the analogy between solutions and gases. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 26, No. 159, pp. 81-105.