Osmotic Flow of Water across Permeable Cellulose Membranes

Abstract

Direct measurements have been made of the net volume flow through cellulose membranes, due to a difference in concentration of solute across the membrane. The aqueous solutions used included solutes ranging in size from deuterated water to bovine serum albumin. For the semipermeable membrane (impermeable to the solute) the volume flow produced by the osmotic gradient is equal to the flow produced by the hydrostatic pressure RT AC, as given by the van't Hoff relationship. In the case in which the membrane is permeable to the solute, the net volume flow is reduced, as predicted by the theory of Staverman, based on the thermodynamics of the steady state. A means of establishing the amount of this reduction is given, depending on the size of the solute molecule and the effective pore radius of the membrane. With the help of these results, a hypothetical biological membrane moving water by osmotic and hydrostatic pressure gradients is discussed.The processes of secretion and absorption in the body have often been assumed to require a movement of water in response to an osmotic gradient. By this hypothesis, a gradient in water activity is produced by the absorption or secretion of a solute. Usually this solute is a small ion or molecule, to which the membrane may be permeable. The influence of a given concentration difference of the solute on the osmotic movement of water depends on the extent of such permeability, or "leakiness." Staverman (1), in a theoretical treatment of this problem using the methods of irreversible thermodynamics, has introduced a correction factor or into the van't Hoff expression for the osmotic pressure due to the solute. In the present work, the Staverman factor or has been determined for a number of different solutes, in conjunction with three cellulose membranes which have been physically characterized. A systematic means of predicting or from the properties of the membrane is given, and the use of or in constructing models of the transporting membrane Dr.

Two Sites of Bile Formation as Determined by Mannitol and Erythritol Clearance in the Guinea Pig*

“…This limiting slope is the ratio of pore areas accessible to solute and solvent. The intercept of the asymptote at zero flow is equal to D3,(A3,/L)a, where a is the Staverman reflection factor, 1 -A.,/AW ( 11,12).…”

Ionic Permeability and Electrical Potential Differences in Necturus Kidney Cells

“…For non-electrolytes, Durbin (33) (34). Thus, the permeability coefficient, Po, derived from cell swelling experiments, is:…”

The roles of paracellular and transcellular pathways and submucosal space in isotonic water absorption by rabbit ileum.

“…That water can be absorbed by epithelial systems against an apparent osmotic gradient was initially explained by the proposal that there were active transport mechanisms for translocating water (Parsons & Wingate, 1961). The demonstration that the paradoxical movement of water could be effected by an intraepithelial compartment which was hypertonic to the mucosal solution as a consequence of salt transport (Curran, 1960;Durbin, 1960;Curran & McIntosh, 1962) has been a viable alternative which has received much experimental support. There is little consensus, however, on the intraepithelial locations) of the proposed hypertonic compartment and the osmotic gradients and hydraulic conductivities (LP) necessary to achieve isotonic transport (see Weinstein & Stephenson, 1981).…”