Ca2+ and cyclic AMP in regulation of intestinal Na, K, and Cl transport.

Abstract

This review is an update of the current understanding of how Ca2+ and cAMP regulate mammalian small intestinal and colonic electrolyte transport. We review the transport processes present in plasma membranes of absorptive and secretory epithelial cells and the way these processes are affected by Ca2+ and cAMP. Studies of intestinal electrolyte transport are complicated by several factors, including the presence, and often simultaneous function, of both absorptive and secretory processes, and by the presence of multiple cell types. A cultured cell line that retains the electrolyte transport properties of the intact tissue would greatly simplify investigation. However, to date neither a transporting small intestinal nor an intestinal absorptive cell line has been developed. A CI­ secreting human colonic epithelial cell line, named T-84, has been reported (1 �-17), but these studies must be interpreted with the realization that such cells do not represent the normal colon, but a cancer cell line. It is generally believed that electrolyte absorption and secretion are carried out by two separate epithelial cell types (38). The absorptive cells are thought to be present only on the villus of small intestine and on the surface of the colon, while the secretory cells are mostly present in the crypts.