Lubiprostone is a locally-acting chloride-channel activator that increases intestinal secretion. In doing so, it increases intestinal motility, thus aiding the passage of stool and relieve the symptoms associated with chronic idiopathic constipation. Lubiprostone acts by specifically activating ClC-2 chloride channels, which is a normal constituent of the apical membrane of the human intestine, in a protein kinase A action independent fashion. Activation of ClC-2 chloride channels causes an efflux of chloride ions into the lumen, which in turn leads to an efflux of sodium ions through a paracellular pathway to maintain isoelectric neutrality. As a result, water follows sodium into the lumen in order to maintain isotonic equilibrium, thereby increasing intestinal fluid secretion. By increasing intestinal fluid secretion, lubiprostone increases motility in the intestine, thereby increasing the passage of stool and alleviating symptoms associated with chronic idiopathic constipation. Activation of ClC-2 chloride channels may also stimulate the recovery of muscosal barrier function by restoring tight junction protein complexes in the intestine. Patch clamp cell studies in human cell lines have indicated that the majority of the beneficial biological activity of lubiprostone and its metabolites is observed only on the apical (luminal) portion of the gastrointestinal epithelium.