Ion-mediated water flow. II. Anomalous osmosis

Anomalous osmotic water flows may be the basis of the hypotonicity of gastric juice sampled at low rates of secretion. The anomalous osmotic flows of water produced by the exchange of hydrogen and a series of cations across the three membranes used in the electroosmotic studies (Paper I) have been obtained. The solvent flow results in part from the momentum imparted by the moving ions to the water contained in the membrane matrix. The physical parameters that regulate the rate of bi-ionic exchange and the accompanying anomalous osmotic solvent flows are: the hydration states of the membranes; the molarities of the membranes and the mobilities of the exchanging ions which are a function of ion size. Each ion in the exchange produces a flow of liquid. Assuming that the ions do not interact with one another in the membrane, the anomalous osmotic flux was assumed to be the sum of the water flows produced by each permeant ion. The anomalous osmotic flux produced by a bi-ionic exchange was calculated from electroosmotic coefficients ([EO]cation and [EO]Cl) and the ion-exchange rates. The calculated values were all 10 to 60% less than the observed values. Part of these differences may have resulted from concentration gradients in unstirred boundary layers adjacent to the membrane which caused an osmotic flow of water in the direction of net water movement. As in the stomach, the sodium-hydrogen exchange produced a hypotonic solution.