The Kedem-Katchalsky equations as applied for describing substance transport across biological membranes

The classical version of the Kedem-Katchalsky equations is suitable for describing substance transport in membrane systems with well-stirred bathing solutions. However, when dealing with biological reality we are faced with a more complicated situation. For instance, in the living cell one can distinguish the central bulk area where the cytoplasm is well stirred due to its natural streaming and a certain relatively thin layer adjacent to the plasma membrane where there is no stirring. In such a situation, the passive transport of substance can be well described using the Kedem-Katchalsky equations in their more general form [1], The equations can, however, be applied provided the membrane boundary unstirred layers of cytoplasm are treated as diffusion layers. This has been shown in detail in the present work.