Adaption to environmental stresses is vital for the survival of all organisms living in any environment. Two of the major environmental factors in the deep sea environment are high hydrostatic pressure and high salt concentration. Hydrostatic pressure and osmotic pressure share similarities in their effects on organisms living in the deep sea but this overlap has been little explored. Major studies from Japan and California over the last 40 years have shown the effects of hydrostatic pressure on bacteria from the deep sea (see [1] for a review). These are complemented by work by Yancey et al. [2] showing that specific solutes accumulated in response to osmotic pressure in fish have the ability to enhance resistance to hydrostatic pressure. However, this work has been done in vitro or with larger organisms and not much is known about the overlap of osmotic and hydrostatic pressure in bacteria. In this study I investigated the effects of osmotic and hydrostatic pressure on two model organisms: Photobacterium profundum and Escherichia coli. In order to accomplish this task I developed novel imaging equipment which allows for high resolution imaging of bacteria at pressure. I also developed a new method of growing bacteria in 96-well plates at high pressure, which lead to the identification of a hierarchy of genes essential for the growth of E. coli at pressure. I used the same 96-well plate technique to monitor the growth of P. profundum at differing osmotic and hydrostatic pressures. Furthermore I also attempted to analyse the solutes accumulated by different strains of P. profundum in response to osmotic and hydrostatic pressures.

In 1897 Davenport measured the wet and dry weights of amphibian embryos from the stage of hatching onwards. He observed that there was a continuous increase in the wet weight but that the dry weight remained constant until the embryo began feeding. From this he concluded that "growth is due chiefly to imbibed water". Schaper (1902) noted a similar constancy of dry weight from the early tail bud stages until the time of feeding in embryos of Rana fusca. These early observations have been confirmed by Dempster (1933) who, working with Amblystoma punctatwn, extended his experiments to include the earliest developmental stages. The increase in volume, and hence the growth, of amphibian embryos is therefore due to the uptake of water from the environment. Many embryologists have attempted to correlate this water uptake with the osmotic pressure of the embryos. The early work in this field has been extensively reviewed by Needham (1931).

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 63-69).

Osmosis is a phenomenon of critical importance in a variety of processes ranging from the transport of ions across cell membranes and the regulation of blood salt levels by the kidneys to the desalination of water and the production of clean energy using potential osmotic power plants. However, despite its importance and over one hundred years of study, there is an ongoing confusion concerning the nature of the microscopic dynamics of the solvent particles in their transfer across the membrane. In this thesis the microscopic dynamical processes underlying osmotic pressure and concentration gradients are investigated using molecular dynamics (MD) simulations. I first present a new derivation for the local pressure that can be used for determining osmotic pressure gradients. Using this result, the steady-state osmotic pressure is studied in a minimal model for an osmotic system and the steady-state density gradients are explained using a simple mechanistic hopping model for the solvent particles. The simulation setup is then modified, allowing us to explore the timescales involved in the relaxation dynamics of the system in the period preceding the steady state. Further consideration is also given to the relative roles of diffusive and non-diffusive solvent transport in this period. Finally, in a novel modi cation to the classic osmosis experiment, the solute particles are driven out-of-equilibrium by the input of energy. The effect of this modi cation on the osmotic pressure and the osmotic ow is studied and we find that active solute particles can cause reverse osmosis to occur. The possibility of defining a new "osmotic effective temperature" is also considered and compared to the results of diffusive and kinetic temperatures.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 107-121).

This dissertation studies the thermodynamic and structural properties of aqueous dispersions of ionic microgels ? soft colloidal particles composed of cross-linked polymer gels that swell in a good solvent. Starting from a coarse-grained model of microgel particles, we perform computer simulations and theoretical calculations using two complementary implementations of Poisson- Boltzmann (PB) theory. Within the framework of a cell model, the nonlinear PB equation is exactly solved and used to compute counterion distributions and osmotic pressures. By varying the free energy with respect to microgel size, we obtain exact statistical mechanical relations for the electrostatic component of the single-particle osmotic pressure. Explicit results are presented for equilibrium swelling ratios of charged microcapsules and of charged cylindrical and spherical microgels with fixed charge uniformly distributed over the surface or volume of the particle. Molecular dynamics simulations validate the theoretical findings. In the second method, within a one-component model framework, based on a linear-response approximation for effective electro- static interactions, we develop Monte Carlo (MC) simulations to compute the equilibrium swelling ratio, bulk osmotic pressure, radial distribution function, and static structure factor. Results presented in this dissertation demonstrate that swelling of ionic microgels increases with increasing microgel charge and decreases with increasing concentration of salt and microgels. In addition, results demonstrate that the microion distributions and osmotic pressure determine equilibrium swelling of microgels. Cell model predictions for bulk osmotic pressure agree well with data from MC simulations of the one-component model. The MC simulations also provide access to structural properties and to swelling behavior of microgels in highly concentrated suspensions. Taken together, results obtained in this work provide insight into factors of importance for practical use of microgels as drug delivery systems, in tissue engineering, and for other biomedical applications.

No description available.

No description available.

Osmotic stress is a potent regulator of the normal function of cells that are exposed to osmotically active environments under physiologic or pathologic conditions. The ability of cells to alter gene expression and metabolic activity in response to changes in the osmotic environment provides an additional regulatory mechanism for a diverse array of tissues and organs in the human body. In addition to the activation of various osmotically- or volume-activated ion channels, osmotic stress may also act on the genome via a direct biophysical pathway. Changes in extracellular osmolality alter cell volume, and therefore, the concentration of intracellular macromolecules. In turn, intracellular macromolecule concentration is a key physical parameter affecting the spatial organization and pressurization of the nucleus. Hyper-osmotic stress shrinks the nucleus and causes it to assume a convoluted shape, whereas hypo-osmotic stress swells the nucleus to a size that is limited by stretch of the nuclear lamina and induces a smooth, round shape of the nucleus. These behaviors are consistent with a model of the nucleus as a charged core/shell structure pressurized by uneven partition of macromolecules between the nucleoplasm and the cytoplasm. These osmotically-induced alterations in the internal structure and arrangement of chromatin, as well as potential changes in the nuclear membrane and pores are hypothesized to influence gene transcription and/or nucleocytoplasmic transport. A further understanding of the biophysical and biochemical mechanisms involved in these processes would have important ramifications for a range of fields including differentiation, migration, mechanotransduction, DNA repair, and tumorigenesis. / Dissertation

Neste trabalho aplicou-se a metodologia diferencial para o cálculo do equilíbrio osmótico dentro da abordagem de Lewis-Randall para sistemas multisolventes. Nessa abordagem, são obtidas equações diferenciais que relacionam pressão e composição do sistema na condição de potencial químico constante dos solventes: o estado de equilíbrio osmótico é calculado integrando-se as equações, obtendo-se a curva de pressão osmótica em função da concentração do soluto. Essas equações não têm solução analítica, mas foram numericamente integradas para sistemas cuja não idealidade seja descrita pelo modelo UNIQUAC. A metodologia foi aplicada na análise de sistemas em que ocorre equilíbrio de fases líquido-líquido, o que em princípio corresponde ao teste mais severo a que pode ser submetida. A comprovação da eficácia da metodologia foi feita por meio da verificação das relações de equilíbrio nos passos intermediários e pela equação de Gibbs-Duhem. Os resultados mostraram que a abordagem é bastante confiável, e que o equilíbrio é corretamente calculado para uma variedade de situações. Foi possível discernir os casos em que é admissível utilizar um pseudo-solvente na descrição do equilíbrio osmótico (sistemas cujos solventes apresentam estruturas semelhantes, sem interação preferencial), e situações em que o cálculo pode não levar a resultados adequados (sistemas em que os solventes apresentem miscibilidade parcial). Os programas desenvolvidos são genéricos e, portanto, podem ser usados para o cálculo do equilíbrio osmótico em qualquer sistema descrito pela equação UNIQUAC. / A differential approach to the calculation of osmotic equilibrium of multisolvent systems within the Lewis-Randall framework is presented in this work. Differential equations relating pressure and composition at constant solvent chemical potential are developed, through whose integration the osmotic equilibrium is calculated. The curves of osmotic pressure as functions of the solute concentration cannot be analytically calculated, and were obtained through numerical integration. The methodology was used to calculate osmotic equilibrium for systems described by the UNIQUAC equation presenting liquid-phase split, which presumably corresponds to the most severe test. The approach was verified by checking the equilibrium conditions at intermediate points and also by checking the Gibbs-Duhem equation. The results show that the methodology is reliable and that the osmotic equilibrium can be correctly calculated for many situations. It was possible to identify the circumstances wherein a pseudo-solvent can be defined (systems whose solvents show similar structures, without presenting preferential interactions), and wherein the calculation may lead to unreliable results (systems wherein the solvents present partial miscibility). The computer programs developed are not specific, and can therefore be used to calculate osmotic equilibrium for any systems described by the UNIQUAC equation.