Osmotic regulation

Cells selected for tolerance to water stress have been demonstrated in a number of plant species (Handa et al., 1983 Heyser Nabors, 1981 Stavarek Rains, 1984b). High molecular weight PEG is commonly used to induce water deficits (Hasegawa et al., 1984). This provides an opportunity to evaluate intracellular osmotic adjustment of plants exposed to water stress. If information is desired on the effect of specific osmotic substances on cellular adjustment to osmotic stress PEG can be used as an independent osmotic regulator and/or in combination with an absorbable osmoticum. In these situations the interaction of osmoticum produced by the cell with the osmoticum absorbed by the cell can be evaluated. 

Cells exposed to excessive levels of salinity have to acquire essential nutrients from a milieu with a preponderance of ions that are potentially toxic and non-essential. In this ionic environment the success of a plant cell will require intracellular tolerance and/or specific acquisition of nutrients essential for normal metabolic functioning. The cell is also exposed to an unfavourable water balance with an absolute requirement to maintain an internal osmotic regulation that favours uptake of water into the cell (Stavarek Rains, 1984 ). 

Albumin is the most abundant (about 55%) of the plasma proteins. An important function of albumin is to bind with various molecules in the blood and serve as a carrier protein, transporting these substances throughout the circulation. Substances that bind with albumin include hormones amino acids fatty acids bile salts and vitamins. Albumin also serves as an osmotic regulator. Because capillary walls are impermeable to plasma proteins, these molecules exert a powerful osmotic force on water in the blood. In fact, the plasma colloid osmotic pressure exerted by plasma proteins is the only force that retains water within the vascular compartment and therefore maintains blood volume (see Chapter 15). Albumin is synthesized in the liver. 

Hussy, N., Deleuze, C., Desarmenien, M. G. and Moos, F. C. Osmotic regulation of neuronal activity a new role for taurine and glial cells in a hypothalamic neuroendocrine structure. Prog. Neurobiol. 62 113-134, 2000. 

OPARKA, K.J., WRIGHT, K.M., Osmotic regulation of starch synthesis in potato-tubers, Plant a, 1988, 174, 123-126. 

Typically, functional porins are homotrimers, which assemble from monomers and then integrate into the outer membrane. The general porins, water-filled diffusion pores, allow the passage of hydrophilic molecules up to a size of approximately 600 Daltons. They do not show particular substrate specificity, but display some selectivity for either anions or cations, and some discrimination with respect to the size of the solutes. The first published crystal structure of a bacterial porin was that of R. capsulatus [48]. Together with the atomic structures of two proteins from E. coli, the phosphate limitation-induced anion-selective PhoE porin and the osmotically regulated cation-selective OmpF porin, a common scheme was found [49]. Each monomer consists of 16 (3-strands spanning the outer membrane and forming a barrel-like structure. 

The fundamental process of transferring a solute from the environment, across a cell(s) to the blood involves the common steps of adsorption, influx, intracellular trafficking or distribution, and efflux to the blood. This process applies to physiologically important solutes like Na+ and amino acids, and applies equally to solutes of environmental concern, such as toxic metals. Animals spend a significant portion of their energy budgets on osmotic regulation indeed, at the... 

Transport of thyroid hormones Transport of vitamin A Osmotic regulation of plasma Non-specific carrier... 

Electrochemical functions H, Na, K, Cl, Mg, Ca, HPO Free Ions Osmotic regulation transmission of chemical signals energy production Including light harvesting... 

Tolerance of and/or dependence upon socEurn chloride can be an important consideration in the survival of plants and aquatic animals. This depends upon osmotic regulation rather than sodium specificity. 

Mannitol has often been used as an osmotic regulator in the external solutions, and has been presumed to be inert. It was found to be a respiratory substrate in 15 of 26 species representing 17 families of higher plants, some of which were capable of utilization of mannitol that was equal to that of n-glucose and D-fructose. Oat (Avena sativa), most often used for the cell-wall studies, showed only a slight output of carbon dioxide from labeled mannitol. About 10% of the carbon in the mannitol was converted, with time, into the hemicellulose and cellulose fractions. Only the glucose, and, perhaps, the cellobiose, was labeled.4 ... 

Higgins, C.F., Dorman, C.J., Stirling, D.A., Waddell, L., Booth, I.R., May, G. Bremer, E. (1988). A physiological role for DNA supercoiling in the osmotic regulation of gene expression in Salmonella typhimurium and Escherichia coli. Cell 52, 569-84. 

Krogh, A. (1939). Osmotic regulation in aquatic animals. London, 242 pp. 

The synthesis of several proteins playing key roles in osmotic regulation is increased following exposure to hyperosmotic stress (reviewed in Burg et al., 1997). Transporters for glycine betaine, taurine, and inositol all increase in abundance over a period of several hours. This up-regulation of transporter activity... 

Bremer (1988). A physiological role for DNA supercoiling in the osmotic regulation of gene expression in S. typhimurium and E. coli. Cell 52 569-584. 

Kiiltz, D. (2000). Osmotic regulation of DNA activity and the cell cycle. In Environmental Stressors and Gene Responses, pp. 157-179, ed. K.B. Storey and J. Storey, New York Elsevier. 

Prabakaran, D., Singh, R, Jaganathan, K. S., and Vyas, S. P. (2004), Osmotically regulated asymmetric capsular systems for simultaneous sustained delivery of anti-tubercular drugs,/. Controlled Release, 95, 239-248. 

Kapus, A., Szaszi, K., Sun, J., Rizoli, S., and Rotstein, O.D., 1999, Cell shrinkage regulates Src kinases and induces tyrosine phosphorylation of cortactin, independent of the osmotic regulation of Na/HHexchangers. J. Biol. Chem. 274(12) 8093-8102. 

Wiese, T.J. et al., 1996, Osmotic regulation of Na-myoinositol cotransporter mRNA level and activity in endothelial and neural cells. Am. J. Physiol. 270(4 Pt 1) C990-C997. 

B. thuringiensis crystals are first solubilized in the midgut of susceptible insects, followed by activation of the protoxins to active toxins by midgut proteases. The activated toxins then bind to midgut membrane receptors, insert into the apical membrane and form pores. Formation of the pores causes loss of osmotic regulation, and eventually leads to cell lyses, which is thought to be responsible for insect death [4,5]. 

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