Thermodynamic analysis of the permeability of biological membranes to non-electrolytes

Abstract

The application of the conventional permeability equations to the study of biological membranes leads often to contradictions. It is shown that the equations generally used, based on two permeability coefficients—the solute permeability coefficient and the water permeability coefficient—are incompatible with the requirements of thermodynamics of irreversible processes. The inconsistencies are removed by a thermodynamic treatment, following the approach of Staverman, which leads to a three coefficient system taking into account the interactions: solute-solvent, solute-membrane and solvent-membrane. The equations derived here have been applied to various permeability measurements found in the literature, such as: the penetration of heavy water into animal cells, permeability of blood vessels, threshold concentration of plasmolysis and relaxation experiments with artificial membranes. It is shown how the pertinent coefficients may be derived from the experimental data and how to choose suitable conditions in order to obtain all the required information on the permeability of the membranes. The significance of these coefficients for the elucidation of membrane structure is pointed out.