Modelling of electrolyte transport in renal and intestinal epithelia. Implications for transport defects

Epithelia can be classified as "leaky" and "tight epithelia" due to their conductive properties and their modes of solute transport. Both the proximal segment of the nephron and the intestinal tract are "leaky" whereas the distal nephron and the colon are "tight". Consequently, inborn errors and exogenous disorders of solute transport often involve both the proximal tubule and the small intestine. In addition, effects on ion and water transport in the distal nephron closely resemble those in the large intestine. Models of solute transport in leaky and tight epithelia are presented employing porter systems known in mammalian tissues. These porter systems are discussed as possible sites of transport defects and as targets for pharmacological agents.