CELL BIOLOGY AND ACTIVE-TRANSPORT PROCESSES IN THE COLON

The colon is a complex and highly differentiated organ evolved to absorb electrolytes and water from the terminal products of small intestinal digestion. Recently, it has attracted attention as a potential site for drug absorption after oral administration. However, use of this region of the gastrointestinal tract is potentially more complex than the upper intestine. It is necessary to consider the colonic environment, transport capabilities, metabolism and site-specific release of the drug in the large intestine. These factors and their influence on drug absorption are not as fully understood as they are in the rest of the gastrointestinal tract. However, increasingly as it is discovered that drugs may be poorly absorbed or highly degraded in the small intestine, the colon is being considered as an alternative site for drug absorption, which may offer new opportunities for the development of orally available drug formulations. This review aims to outline the cell biology of the colon and describe the biochemical processes, particularly ion transport, that account for the properties of this organ.