Molecular physiology of colonic epithelial sodium absorption.

The colon is the final site for fluid and electrolyte conservation in the gastrointestinal system. Active absorption of sodium ions generates driving forces for the movement of fluid and other electrolytes, and is under hormonal control of mineralocorticoids for maintaining body homeostasis. Sodium is absorbed through a transcellular route, and the main regulatory sites are epithelial sodium channels (ENaCs), located in the apical cell membrane. Recently these channels have been cloned, and were also found in other cells from kidney to lung. They belong to a newly discovered ancient superfamily of channels which dates back in evolution to nematodes. Physiological investigations of the molecular diversity of this channel family not only provides new information of an important group of biomolecules, but opens up routes for the understanding and treatment of various diseases ranging from kidney failure to high blood pressure.