Intestinal Chloride Secretion: Cyclic Amp and Ca2+ Interactions
Intestinal epithelium is functionally polarized in that it is modeled as a single, homogeneous intracellular compartment bounded by an apical and a basolateral membrane with different ion transport properties. Like other ionic species, chloride transport across the epithelial barrier is achieved through the involvement of distinct pathways acting in concert and distributed to the basolateral and luminal membrane of the cell. Histamine, a mast cell product, may activate both Ca2+ and cyclic adenosine monophosphate (cAMP)-dependent pathways. In T84 cells that lack cyclooxygenase activity, the mechanism of chloride secretion promoted by histamine resembled that of carbachol in that it was potentiated by cAMP agonists. A phospholipase D (PLD) active on phosphatidylcholine (PC) and phosphatidylethanolamine has been partially purified from rat brain. During signal transduction the cleavage of phosphodiesters of PC is a widespread phenomenon that can occur by participation of phospholipase C and PLD.