Considerations on different thermodynamic models for mass transport across membranes

The linear Kedem-Katchalsky phenomenological and practical equations are examined in order to show their different information content and the usefulness of the latter as a starting point for a non-linear treatment. A simplified analytical treatment of a series array of membranes, following the Patlak-Goldstein-Hoffman method, is subsequently compared with the Kedem-Katchalsky treatment and with the pseudo-electrical network approach of Mikulecky, showing that the analytical and network treatments give the same results in several instances. A comparison with the models of epithelial transport proposed by Weinstein and Stephenson indicates that the series array model includes, as a particular case, the results obtained by means of the standing gradient osmotic flow model.