Studying transport processes in absorptive epithelia

Abstract

Abstract Transport processes in epithelia have traditionally been studied in a variety of organ and tissue preparations from different species. However, native epithelial tissues are complex and contain many different cell types. Monolayer cultures from established epithelial cell lines have the advantages of being structurally simple, homogeneous, and easy to manipulate. Transport studies in epithelial monolayers are, therefore, often easier to perform and interpret (1). The major disadvantage of epithelial cell cultures is that in most situations they are unlikely to serve as a complete substitute for the more complex normal epithelium. Moreover, epithelial cells in culture may express carriers and enzymes in a different or more variable manner than seen in vivo. Despite these disadvantages, recent studies in epithelial cell monolayers have brought new insights into the functions of a variety of transport mechanisms of endogenous as well as exogenous molecules such as drugs. The aim of this chapter is to present some of the protocols used in our laboratory to study passive and active drug transport processes across monolayers of the human intestinal epithelial cell line Caco-2 grown on permeable supports (Figure 1). However, before such studies are performed it is important to know how to culture and assess the integrity of the cell monolayers on permeable supports in a reproducible manner. Methods for such characterization are presented initially. The methods for studying integrity and transport processes are general and should, therefore, be applicable to solutes other than drugs and to epithelial cell cultures other than Caco-2.