Theoretical study of the molecular transport across biologically active membranes was based on the experiments concerning absorption and digestion of nutrients on the intestinal epithelium. It was demonstrated that the surface membranes of enterocytes possess both digestive and barrier functions. The barrier functions were predicted to be based on the reversible water flows normal to the membrane surface.
( A.Ugolev, V.Gusev, A.Gruzdkov - The three - compartmental enzyme system of the enterocyte relating to its digestive and barrier functions, Adv..Physiol. Sci. Vol.29, Gastro-intestinal Defense Mechanisms, Budapest, 1981, p.303-314. )In order to explain the high efficiency of the substate transport across membranes observed experimentally the new transport mechanism - "transorption" was proposed, which deals with diffusion process modified by mobile adsorption sites inside the diffusion area. It was also shown that the well known high selectivity of the transport conveyer towards the nutrients can be explained by the geometric characteristics of the small intestinal surface and the adsorption process in viscinity of the cell membrane. ( V.Gusev, A.Gruzdkov, A.Ugolev - Mathematical modelling in study of digestion and transport. In: Membrane digestion. New facts and concepts. Ed. A.Ugolev, Moscow, Mir Publishers,1989, p.216-246. )