Symports and Antiports in Epithelial Cell Volume Regulation
Epithelial cells, like nonpolar cells, depend for their viability on the maintenance of a constant intracellular environment. Unlike nonpolar cells, epithelial cells transport solutes and water between the compartments they separate and thereby serve to maintain the homeostasis of the organism. Because the latter function often involves the separation of solutions of vastly different contents, the cells are from time to time exposed to anisotonic media. Furthermore, because at least one side of these cells is generally permeable to water, the cell volume may change drastically under such circumstances, and the ability to regulate volume then becomes important for survival. In fact, most epithelial cells possess mechanisms whereby they can regulate the volume of their cells back toward a normal volume after osmotic swelling or shrinking.