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PubMed1995

Central angiotensin II induces thirst-related responses in an amphibian.

Angiotensin II (A-II), a potent inducer of thirst-related behavior in many vertebrate species, was injected into the third ventricle of the brain of the spadefoot toad, Scaphiopus couchii. Following injection of 10 ng A-II the animals demonstrated a significant increase in water absorption response (WR) behavior, in which toads press their ventral skin to a moist surface and absorb water by osmosis. This increase in the frequency of WR behavior was positively correlated with an increase in water gain during a 2-hr period indicating that centrally injected A-II stimulates water intake by this amphibian species. We have previously demonstrated that WR behavior is also induced by intraperitoneal (i.p.) injections of A-II in several anuran species, including S. couchii. Thus, amphibians, like other vertebrates, demonstrate an increase in water intake in response to either centrally administered or circulating A-II. A second series of experiments was conducted to determine whether the above response to A-II might be secondary to increases in the circulating levels of aldosterone (ALDO) or antidiuretic hormone because the release of both of these hormones has been shown by others to be stimulated by A-II. Scaphiopus couchii injected i.p. with either ALDO or arginine vasotocin in dosages of 1, 10, and 100 micrograms/100 g body weight showed no increase in WR behavior relative to toads injected with saline alone. These results suggest that A-II acts directly on the brain of S. couchii to induce WR behavior.

Aldosterone↗
PubMed1999

Calculation of Zeta Potential from Electrokinetic Measurements on Titania Plugs.

The O'Brien theory developed for the electrical conductivity and electro-osmosis in porous plugs consisting of nonconducting particles has been applied for the calculation of zeta-potentials from conductivity and streaming potential measurements at two pH values, 3.3 and 6.5 or 5.8, on plugs composed of titania (undoped and doped with W6+ and Li+ ions) particles. The particles have been prepared both by precipitation (continuous crystallization at constant supersaturation) and by the sol-gel method. It was found that O'Brien's theory is also applicable in n-type semiconductor particles, such as titania (doped and undoped). Specifically, for the correct determination of zeta-potentials measured in solutions of relatively low ionic strength, it is necessary to take into account surface conduction behind the shear plane, for all samples measured at pH 3.3, a value considerably lower than the isoelectric point (i.e.p.) of titania. Under these conditions the surface charge of the suspended titania particles is high, and consequently the contribution of surface conductance to the conductivity of the plug is significant. The effect of surface conduction behind the shear plane on the calculation of zeta-potential is enhanced for the Li+-doped preparations due to the increase of surface conductivity caused by doping with Li+. Measurements of the streaming potential for the samples prepared with the sol-gel method were made at pH 6.5 (5.8 for the undoped titania); i.e., near the pH corresponding to the i.e.p., correct values of zeta-potential may be obtained in suspensions even at low ionic strength without taking into account the polarization of the double layer due to surface conduction, by applying the primitive Smoluchowski theory. This treatment is valid because at pH values near the i.e.p. the surface charge of the particles is very low, and consequently surface conductance is negligible compared with the conductivity of the plug. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Electrophoretic Motion of a Prolate Spheroid in Electro-osmotic Flow Developed in a Flat Cell.

Electrophoretic motion is analyzed for a neutrally buoyant, non-Brownian prolate spheroid suspended in an electro-osmotic flow developed in a flat microelectrophoresis cell. Neglecting the double-layer deformation, the trajectory and orientation of the spheroid is computed to assess the significance of particle motion in a lateral direction during an electrophoresis experiment. The double-layer thickness of the spheroid is arbitrary. In a closed microelectrophoresis system the electro-osmosis results in a parabolic flow field. During a short period of time (several seconds) the spheroid may deviate significantly in a lateral direction from a straight path parallel to the applied electric field. During a longer period of time (several minutes) the spheroid undergoes a sinuous motion in which it translates periodically back and forth across a straight path along the main flow direction. The spheroid may also translate along a closed trajectory. In all cases the orientation of the spheroid follows the equation for Jeffery orbit. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Electroosmotic Flow through an Annulus.

The electro-osmosis through an annulus is investigated. The electric potential and flow velocity profile are obtained by solving the linearized Poisson-Boltzmann equation and the Stokes equation. Both the thin and thick double layer limits are analyzed. Under the condition of thin double layer, the electro-osmotic mobility can be described by the Helmholtz-Smoluchowski equation with a geometry-dependent correction factor. There exist net flows even for zero area-averaged surface charge density due to the curvature differences between the inner and outer walls. The flow direction is determined by the sign of the charge on the inner cylinder. We also found that under certain circumstances the flow direction in an annulus is opposite to that in a capillary with the same sign of the net charge. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Atomic Force Microscopy Studies of Membranes: Effect of Surface Roughness on Double-Layer Interactions and Particle Adhesion.

Atomic force microscopy in conjunction with the colloid (silica) probe technique has been used to quantify the variations in electrical double-layer interactions and adhesion at different locations on a rough reverse osmosis membrane (AFC99) surface in NaCl solutions. Prior scanning of the membrane surface with the colloid probe allowed precise location for force measurements. The membrane surface was composed entirely of peaks and valleys with a surface roughness substantially greater than that of most other types of polymeric membranes. The magnitude of the electrical double-layer repulsion between the colloid probe and the membrane at peaks on the membrane surface was greatly reduced compared to that in the valleys. Nevertheless, adhesion of the colloid probe was lower at the peaks on the membrane surface than in the valleys with the difference increasing with decreasing salt concentration, and reaching a factor of more than 20 in 10(-3) M solution. The study shows that minimization of membrane fouling by colloids could be achieved by choosing membranes with a roughness periodicity preventing penetration of foulants into valleys on the surface. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Transport of Water and Ions Through a Clay Membrane.

A model for hindered transport of water and ions is used to predict transient flow through a clay membrane caused by an initial difference in the concentration of salt solutions in reservoirs on the two sides of the membrane. Transport is assumed to be controlled by three coefficients, which are analogous to the permeability, salt diffusivity, and salt reflection coefficient of the membrane. Initial fluid motion is caused by osmosis, leading to a buildup of pressure on one side of the membrane. However, the clay forms an imperfect ion exclusion membrane and the final steady state is one of equal concentrations and pressures on the two sides of the membrane. The time-dependent differences in pressure and salt concentration across the membrane are predicted to vary as the sum of two decaying exponentials. When the salt reflection coefficient is small, one time scale governs Darcy flow through the membrane and another the diffusion of salt. Experimental results confirm the analysis. Although the salt concentration in the reservoirs was monitored in the experiments, estimates of the transport coefficients can be obtained by measuring only the pressure change across the membrane. Copyright 2000 Academic Press.

Journal Article↗
PubMed2001

Modeling Disjoining Pressures in Submicrometer Liquid-Filled Cylindrical Geometries.

This work develops models for calculating the disjoining pressures of a cylindrical fluid "plug", specifically in submicrometer cylindrical pores. This modeling produces closed-form, cylindrical-pore disjoining pressures for London/van der Waals and solute/pore-wall adsorption interactions, which are the slit-pore models with the characteristic pore size replaced by the radius and multiplied by 6, resulting in a 48-fold or more increase in magnitude. In addition, this work contains a numerical solution for electrostatic interactions. The result of the numerical solution was a 9-fold increase in the modeled disjoining pressure compared to that in the slit-pore model. The cylindrical models may apply to the chemical coating of the interior walls of cylindrical pores or to the thermodynamics within droplets after the breakup of a fluid coating a surface. However, the application used as the base case in this paper is the extension of transport and thermodynamic laws for porous media, previously developed with capillary pressure models, to fully saturated porous media with submicrometer-sized pores. As such, the models could apply to mass transport in ultrafiltration, nanofiltration, and reverse-osmosis membranes. Copyright 2001 Academic Press.

Journal Article↗
PubMed1997

The origin of life and its methodological challenge.

The problem of the origin of life is discussed from a methodological point of view as an encounter between the teleological thinking of the historian and the mechanistic thinking of the chemist; and as the Kantian task of replacing teleology by mechanism. It is shown how the Popperian situational logic of historic understanding and the Popperian principle of explanatory power of scientific theories, when jointly applied to biochemistry, lead to a methodology of biochemical retrodiction, whereby common precursor functions are constructed for disparate successor functions. This methodology is exemplified by central tenets of the theory of the chemo-autotrophic origin of life: the proposal of a surface metabolism with a two-dimensional order; the basic polarity of life with negatively charged constituents on positively charged mineral surfaces; the surface-metabolic origin of phosphorylated sugar metabolism and nucleic acids; the origin of membrane lipids and of chemi-osmosis on pyrite surfaces; and the principles of the origin of the genetic machinery. The theory presents the early evolution of life as a process that begins with chemical necessity and winds up in genetic chance.

Animals↗
PubMed1989

The Gibbs-Duhem equation in membrane transport.

It is argued that the Gibbs-Duhem equation alone cannot be used for deriving conclusions about the pressure gradient in membrane permeation. Statements regarding spatial variation of pressure in conjunction with chemical potential gradients of the components can legitimately be drawn from an equation that results from a combination of the G-D equation and the mechanical equilibrium equation. The derived equation has been applied here for explaining the mechanics of osmosis. In a further application, the frictional model has been improved here because the driving force also includes the membrane-solute potential interaction, thus allowing the solute partition coefficient to appear in the calculations naturally. By recognizing that because of the membrane-solution interaction, external forces of both potential and frictional character are present, the dissipation function is shown to depend explicitly on the centre-of-mass velocity. Thus the reference velocity for diffusive fluxes cannot be chosen arbitrarily, making Prigogine's theorem invalid in this approach to describing membrane permeation.

Mathematics↗
PubMed1992

Renal, respiratory and ionic regulation in Atlantic salmon (Salmo salar L.) kelts following transfer from fresh water to seawater.

Atlantic salmon may return to the sea after spawning in fresh water. These fish, known as kelts, reportedly show a limited ability to hypoosmoregulate. However, this study shows that fresh-water-adapted kelts exposed to seawater demonstrate rapid adaptation (within 48 h) in osmoregulatory parameters to values characteristics of seawater-adapted salmonids. The urine flow rate falls from 1.2 to 0.2 ml.kg-1.h-1 within 24 h. Over the same period, urine osmolality increases from 48 mosmol.kg-1 to become isosmotic with the plasma, and Mg2+ secretion by the kidney tubules elevates the urine concentration from 0.5 to 100 mmol.l-1. As is characteristic for marine teleosts, kelts drink seawater and process the ingested water in the gut to replace body water lost by osmosis to the hyperosmotic medium. Seawater exposure causes a marked hypoxia, arterial oxygen tension falling by 43% within minutes and persisting for at least 4 days at this low level. This is associated with large changes in blood pH and acid-base balance. The physiological mechanisms involved in adaptation to a hyperosmotic external medium are discussed, and the osmoregulatory capacity of kelts is compared with that of salmon at other stages of the life cycle.

Adaptation, Physiological↗
PubMed1979

A functional model of the rat kidney.

A mathematical model of the nephron was developed by writing a set of material balance equations for the flow of urea, salt and water along the foregoing study and are taken here as a basis, in particular the model configuration of the collecting duct system. The stimulation of the model equatentration profiles which at the ends of the several tubular sections were consistent with the values observed in experimental investigations.e medullary interstitial solute concentration profiles are taken to increase linearly in outer and inner zone. The several transeptithelial fluxes are driven by diffusion, osmosis, solvent drag and active transport. The development of osmotic gradient in the inner medulla is taken here to be caused by active secretion of salt into the descending LImb of Henle's loop. The parameters in the flux equations for all parts of the nephron and the concentration values at the end of each tubular section are determined by collecting and averaging the values given in literature and by extrapolating the measurement data. The simulation of the model equations with these averaged parameters resulted in concentration profiles which at the ends of the several tubular sections were consistent with the values observed in experimental investigations.

Animals↗
PubMed1995

Modelling the mitotic apparatus. From the discovery of the bipolar spindle to modern concepts.

This bibliographical review of the modelling of the mitotic apparatus covers a period of one hundred and twenty years, from the discovery of the bipolar mitotic spindle up to the present day. Without attempting to be fully comprehensive, it will describe the evolution of the main ideas that have left their mark on a century of experimental and theoretical research. Fol and Bütschli's first writings date back to 1873, at a time when Schleiden and Schwann's cell theory was rapidly gaining ground throughout Germany. Both mitosis and chromosomes were to be discovered within the space of thirty years, along with the two key events in the animal and plant reproductive cycle, namely fecondation and meiosis. The mitotic pole, a term still in use to this day, was employed to describe a morphological fact which was noted as early as 1876, namely that the lines and the dots of the karyokinetic figure, with its spindle and asters, looks remarkably like the lines of force around a bar magnet. This was to lead to models designed to explain the movements of chromosomes which take place when the cell nucleus appears to cease to exist as an organelle during mitosis. The nature of those mechanisms and the origin of the forces behind the chromosomes' ordered movements were central to the debate. Auguste Prenant, in a remarkable bibliographical synthesis published in 1910, summed up the opposing viewpoints of the 'vitalists', on the one hand, who favoured the theory of contractility or extensility in spindle fibres, and of those who believed in models based on physical phenomena, on the other. The latter subdivided into two groups: some, like Bütschli, Rhumbler or Leduc, referred to diffusion, osmosis and superficial tension, whilst the others, led by Gallardo and Hartog, focussed on the laws of electromagnetism. Lillie, Kuwada and Darlington followed up this line of research. The mid-20th century was a major turning point. Most of the modelling mentioned above was criticized and fell into disuse after disappearing from research publications and textbooks. This marked the onset of a new era, as electron microscopes made possible the materialization and detailed study of the macromolecular elements of the fibres, filaments and microtubules of the cytoskeleton.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell Biology↗
PubMed1992

Preparation of N-acetylneuraminic acid from delipidated egg yolk.

Egg yolk, a large proportion of the egg, was studied for the preparation of N-acetylneuraminic acid (Neu5Ac). The delipidated hen egg yolk (DEY; 500 kg containing 0.2% w/w, Neu5Ac) was hydrolysed with HCl (pH 1.4) at 80 degrees C and neutralized with NaOH (pH 6.0). The mixture was filtered and electrodialysed until the conductivity was 240 microS cm-1. The filtrate was applied on a column of Dowex HCR-W2 (20-50 mesh), followed by a column of Dowex 1-X8 (200-400 mesh). The latter column was washed with water, and then eluted with a linear gradient of HCO2H (0-2 M). The eluates containing Neu5Ac were concentrated using a reverse osmosis membrane and, finally, rotary evaporated at 40 degrees C. The residue was then lyophilized to yield 500 g Neu5Ac. The purity of Neu5Ac was > 98% (TBA method). HPLC, NMR spectroscopy and TLC chromatography of the product obtained from the DEY showed that Neu5Ac was the sole derivative present in egg yolk. The DEY, a byproduct from egg processing plants, was found to be an excellent source for the large-scale preparation of Neu5Ac.

Amino Acids↗
PubMed1988

A rapid sperm motility bioassay procedure for quality-control testing of water and culture media.

A rapid bioassay procedure is described for quality-control testing water and apparatus used in the preparation of media for gamete and embryo culture. This bioassay is based on the sensitivity of hamster epididymal spermatozoa to contaminants present in water and/or in the culture apparatus. The bioassay is usually performed using a modified Tyrode's solution as the sperm culture medium, although complex media can be used. The sensitivity of this test is greatly enhanced by the absence of protein in the medium. The bioassay has been used to detect impurities in water prepared by a standard cartridge filtration system and to verify that reverse-osmosis pretreatment of water could eliminate the problem. It has also detected toxic contaminants leached from syringe filters during medium sterilization. The bioassay is simple to perform and can be completed in 1 working day. It may be a useful alternative to the conventional mouse embryo tests that are in widespread use in human in vitro fertilization (IVF) laboratories.

Animals↗
PubMed1994

The relationship between carbon and water transport in single cells of Chara corallina.

The hydraulic resistance of the plasma membrane was measured on single internodal cells of Chara corallina using the method of transcellular osmosis. The hydraulic resistance of the plasma membrane of high CO2-grown cells was significantly higher than the hydraulic resistance of the plasma membrane in low CO2-grown cells. Therefore we tested the possibility that the "bicarbonate transport system", postulated to be present in low CO2-grown cells, serves as a water channel that lowers the hydraulic resistance of the plasma membrane. We were unable to find any correlation between agents that inhibited the "bicarbonate transport system" and agents that increased the hydraulic resistance of low CO2-grown cells. We did, however, find a correlation between the permeability of the cell to water and CO2. We propose that the reduced hydraulic resistance of the plasma membrane of the low CO2-grown cells is a function of a change in either the structural properties of the lipid bilayer or the activity of a CO2 transport protein so that under conditions of reduced inorganic carbon, the plasma membrane becomes more permeable to CO2, and consequently to other small molecules, including H2O, methanol and ethanol.

Bicarbonates↗
PubMed1980

Unstirred layer effects in osmotic water flow across gallbladder epithelium.

The standard one-dimensional model of the unstirred layer is applied in a re-examination of the experimental results of Wright, Smulders and Tormey (Wright, E.M., Smulders, A.P., Tormey, J. McD., 1972, J. Membrane Biol. 7:198) who reported large transients in the osmotic flux of water from the serosal to the mucosal side of rabbit gallbladder epithelium. They initiated osmosis by the addition of sucrose to the mucosal bathing solution (initially, approximately 300 nOsm NaCl) and observed that the initial flux was more than ten times its eventual steady-state value; they interpreted this as a consequence of the piling-up of NaCl in the unstirred tissue layer on the serosal side of the epithelium. The present analysis (both steady-state and unsteady) shows that if measured values of layer thickness delta are used, together with reasonable values of the reduced diffusivity of NaCl in the tissue and of the fraction of tissue available for water flow, then one would predict a discrepancy of only about 10%, not tenfold, between the initial and final values of the flux. Thus the standard model is inconsistent with the observations. Furthermore, Wright et al's results cannot be used to infer that the osmotic permeability of epithelial cell membranes is much larger than steady-state measurements on whole epithelia would indicate. Mucosal-to-serosal flow is also analyzed, and in this case a considerably greater osmotic permeability is predicted; this result is consistent with the observed changes in structure of the lateral intercellular spaces when the direction of flow is reversed.

Animals↗
PubMed1994

Bile flow in a mutant Sprague-Dawley rat with defective biliary excretion of glutathione.

The Eisai hyperbilirubinemic rat is a mutant strain of Sprague-Dawley origin with hereditary defects in the biliary excretion of bilirubin glucuronide, glutathione, and several other organic anions. The correlation between bile flow and bile acid excretion rates during taurocholate infusion revealed that bile acid-independent flow was smaller in the mutant than in intact Sprague-Dawley rats (19.3 vs 56.0 microliters/kg per min), while bile acid-dependent flow was similar. The correlation between bile flow and glutathione excretion rates in Sprague-Dawley rats with modified hepatic glutathione levels revealed that a certain portion of bile flow was proportional to the biliary excretion of glutathione, with a coefficient of 551 bile per 1 mol glutathione. One-third of bile acid-independent bile flow in intact Sprague-Dawley rats was accounted for by glutathione osmosis, which feature was absent in the mutant rats.

Animals↗
PubMed2002

The relationship of temperature to desiccation and starvation tolerance of the Mycobacterium avium complex.

Mycobacterium avium grew in media at 14-37 degrees C, and persisted at 4 degrees C and 42 degrees C. The bacteria lost approximately 90% viability after 3 months in reverse-osmosis deionized water at 4-37 degrees C. Cooler temperatures lowered the death rate. Death rates also decreased after a 5- to 10-day starvation adaptation period. Alterations of the steady-state levels of different mycolic acid classes, presumably to facilitate thermoadaptation, were found. Following desiccation, M. avium lost viability at a constant rate (half-life of 2.3 days). This implies that bacilli contaminating dry medical surfaces would persist for short periods of time. The remarkable stress survival exhibited by M. avium further suggests persistence in a range of environmental and clinical settings.

Bacterial Proteins↗