Osmotic expansion

Brading Do your expression cells generate sparks Do you get spontaneous release from the SR in these cells You showed some of these cells where the SR was overloaded with Ca2+, and I wondered whether there is a difference in the behaviour of the SR depending on the amount of intracellular Ca2+. This is going back to this business of stretch-activated channels and whether if you stretch the SR by superfilling it with Ca2+ and getting some osmotic expansion it changes its behaviour. 

The work done dw may be of any kind e.g. electrical, osmotic, expansion against pressure, etc.), or may be a sum of several of these kinds of work, say Stt dp in which case we may write the first law in the form... 

Quartz crystal microbalance studies have shown that the movement of the solvent molecules associated with ions can be considerable. Using PPy prepared in sodium dodecyl sulfate, a mix of both cation- and anion-driven processes was seen when cycled in NaCl, and the mass changes involved indicated that four water molecules moved per Cl and 15 water molecules per Na" " [11]. The role of solvent water molecules has also been examined for PPy in dodecyl benzene sulfonate (DBS), a very widely studied system, where the insertion of cations accounted for only 20% of the mass change upon polymer reduction, indicating that four water molecules were brought into the film with each Na+ [12]. As the electrolyte concentration was changed from 0.1 M to 6 M, the total inserted mass became smaller and the mechanism moved from pure cation transport to an equal amount of anion transport [13]. These results were said to support an osmotic expansion model, whereby the difference in osmotic pressure between the electrolyte and polymer bulk (greater with more dilute electrolyte solutions) drives solvent movement. 

The volume changes of the polymer may result partly from the changes of the polymer backbone, due to the changes of bond lengths and conformation, and partly from osmotic expansion, which is the volume change associated with the solvent movement, of the polymer phase. The osmotic expansion of PPy-DBS was thermodynamically and experimentally described to investigate the osmotic effect on the... 

Bay, L., T. Jacobsen, and S. Skaarup. 2001. Mechanism of actuation in conducting polymers Osmotic expansion, f Phys Chem B 105 8492. 

Alici G, Huynh NN (2007) Performance quantification of conducting polymer actuatois for real applications a microgripping system. lEEE/ASME Trans Mechatron 12 73-84 Bay L, Jacobsen T, Skaarup S, West K (2001) Mechanism of actuation in conducting polymers osmotic expansion. J Phys Chem B 105 8492-8497 Berdichevsky Y, Lo YH (2003) Polymer microvalve based on anisotropic expansion of polypyrrole. MRS Online Proc Libr 782 101-107... 

Theta conditions in dilute polymer solutions are similar to tire state of van der Waals gases near tire Boyle temperature. At this temperature, excluded-volume effects and van der Waals attraction compensate each other, so tliat tire second virial coefficient of tire expansion of tire pressure as a function of tire concentration vanishes. On dealing witli solutions, tire quantity of interest becomes tire osmotic pressure IT ratlier tlian tire pressure. Its virial expansion may be written as... 

Although Eq. (10.50) is still plagued by remnants of the Taylor series expansion about the equilibrium point in the form of the factor (dn/dc2)o, we are now in a position to evaluate the latter quantity explicitly. Equation (8.87) gives an expression for the equilibrium osmotic pressure as a function of concentration n = RT(c2/M + Bc2 + ) Therefore... 

Exxon products appear to release via a unique mechanism. Like other polymer-coated technologies, the penetration of water iato the granule is purely by diffusion. However, as water enters the particle, an osmotic pressure is created as the fertilizer is solubilized. This pressure causes an expansion of the elastomeric coating and the particle swells to many times its original diameter. As the particle swells, the coating becomes increasingly thinner to the point where it caimot contain the internal pressure and the nutrient is released. 

Osmotic adjustment Cell expansion and Morgan Condon,... 

Plant cells selected for tolerance to stress show varied responses to the imposed osmotic gradients. In adapted cells, tolerance to salinity or to water stress was not found to increase proportionately with increases in turgor (Handa et al., 1983 Binzel et al., 1985). It was suggested from these observations and from studies by Heyser Nabors (1981) that no relationship existed between turgor and growth and that stress adaptation may alter the relationship between turgor and cell expansion (see also Chapter 6). 

Cell expansion rate, turgor, osmotic pressure, and water potential of leaf 6 and leaf 11 of wild type and invertase plants... 

We may point out parenthetically that it is usually customary to attribute the expansion to electrostatic repulsions between the net (positive) charges on the polymer molecule which are uncompensated due to loss of counter-ions to the outer solution. It may be shown that the osmotic force owing to the excess of mobile ions within the molecule must be equal to the force of electrostatic repulsion when the molecule is in equilibrium with its surroundings. Hence either point of view is equally satisfactory in principle. The two are, of course, mutually related no net charge would develop in the molecule were it not for the mobile counter-ions, and no excess of mobile ions would be retained to exert an osmotic pressure if it were not for the charges on them. 

Coefficients in the virial expansion of the osmotic pressure as a power series in the concentration c (Chap. XII et seq.). 

Coefficients in the alternative virial expansion of the osmotic pressure (see Eqs. VII-13 and XII-76). 

Understanding the effects of colloid administration on circulating blood volume necessitates a review of those physiologic forces that determine fluid movement between capillaries and the interstitial space throughout the circulation (Fig. 10—5).4 Relative hydrostatic pressure between the capillary lumen and the interstitial space is one of the major determinants of net fluid flow into or out of the circulation. The other major determinant is the relative colloid osmotic pressure between the two spaces. Administration of exogenous colloids results in an increase in the intravascular colloid osmotic pressure. In the case of isosomotic colloids (5% albumin, 6% hetastarch, and dextran products), initial expansion of the intravascular space is essentially that of the volume of colloid administered. In the case of hyperoncotic solutions such as 25% albumin, fluid is pulled from the interstitial space into the vasculature... 

Recall that the reabsorption of Na+ ions is accompanied by reabsorption of Cl- ions, which diffuse down their electrical gradient, and by reabsorption of water, which diffuses down its osmotic gradient. The net result is an expansion of plasma volume and consequently an increase in blood pressure. Therefore, the regulation of sodium reabsorption is important in the long-term regulation of blood pressure. As such, aldosterone and ANP, as well as the factors involved in their release, are discussed further in subsequent sections. 

---