Flows of 22Na in layer-type composite membranes

Abstract

The permeability of 22Na across simple and layer-type composite membranes of parlodion containing different amounts of polystyrenesulfonic acid has been measured as a function of external NaC1 concentration and corrected for the effects of aqueous stationary layers present at the membrane-solution interfaces. It was found that the permeability of 22Na in the two opposite directions across the composite membrane was different whereas it was the same across simple membranes. In both cases, the permeability of 22Na increased with increase in the concentration of the external solution. In the presence of a concentration gradient, the composite membranes generated ±58 mV for a tenfold difference in the concentration and gave values for the permeability of 22Na which were different in the two directions across the membrane. Corrections applied to the two permeability values in the two opposite directions due to the presence of the electric potential difference across the membrane gave values which agreed qualitatively with those measured in the absence of the concentration gradient. The asymmetry or rectification in the permeability of 22Na was attributed to the presence of a permanent Na-solubility gradient in the composite membrane which assisted the flow of Na in one direction (high charge density side to low charge density side of the membrane) and opposed it in the opposite direction. Measurement of distribution of 22Na in the various layers of the composite membrane showed that there was accumulation and depletion of 22Na in the membrane phase, i.e., 22Na concentration profile asymmetric, when 22Na was flowing from the high charge density side to the low charge density side and vice versa, respectively. The need to recognize the existence of such a directional quantity (solubility gradient) and its contribution to fluxes measured across the biological membranes which have a layered structure is pointed out.