Basolateral ion transporters involved in colonic epithelial electrolyte absorption, anion secretion and cellular homeostasis

Electrolyte transporters located in the basolateral membrane of the colonic epithelium are increasingly appreciated as elaborately regulated components of specific transport functions and cellular homeostasis: During electrolyte absorption, Na+/K+ ATPase, Cl- conductance, Cl-/HCO3- exchange, K+/Cl- cotransport and K+ channels are candidates for basolateral Na+, Cl- and K+ extrusion. The process of colonic anion secretion involves basolateral Na+/K+/2Cl-, and probably also Na+/HCO3- cotransport, as well as Na+/K+ ATPase and K+ channels to supply substrate, stabilize the membrane potential and generate driving force respectively. Together with a multitude of additional transport systems, Na+/H+ exchange and Na+/HCO3- cotransport have been implicated in colonocyte pH(i) and volume homeostasis. The purpose of this article is to summarize recently gathered information on the molecular identity, function and regulation of the involved basolateral transport systems in native tissue. Furthermore, we discuss how these findings can help to integrate these systems into the transport function and the cellular homoeostasis of colonic epithelial cells. Finally, disturbances of basolateral electrolyte transport during disease states such as mucosal inflammation will be reviewed.