Chapter 28 - Chloride Transporters as Water Pumps: Elements in a New Model of Epithelial Water Transport

Abstract

This chapter reviews that in epithelial cells and endothelial cells of the blood–brain barrier, cation- Clˉ cotransporters play an important role in the transport of ions. Typically, water or fluid follows the movement of ions. These ion transporters mediate the transport of water, and that proteins directly couple water movement to the transport of substrate. The combination of water, ion and organic nutrient transport has also been found for a variety of other, Clˉ independent, cotransporters. Water and substrate transport in epithelial and endothelial cell layers present some fundamental problems. In the lumen of the small intestine, for example, the presence of high concentrations of glucose and other nutrients, of up to 200 mOsm hyperosmolar to the epithelial cells just after a meal, constitutes a potential threat for osmotic back-flux and dehydration. The chapter also defines that water transport through KCC and NKCC is central for the coupling of substrate and water transport across epithelia and endothelia.