title: Chloride secretory mechanism induced by prostaglandin E1 in a colonic epithelial cell line.
abstract: Confluent T84 monolayers grown on permeable supports and mounted in a modified Ussing chamber secrete chloride (Cl-) in response to prostaglandin E1. The threshold stimulation was observed at 10(-9) M and a maximal effect at 10(-6) M. Unidirectional flux studies showed an increase in both serosal to mucosal and mucosal to serosal Cl- fluxes with 10(-6) M prostaglandin E1; the increase in serosal to mucosal Cl- flux exceeded the increase in mucosal to serosal flux, resulting in net Cl- secretion. Na+ transport was not affected in either direction and the changes in net Cl- flux correlated well with the changes in short circuit current. To identify the electrolyte transport pathways involved in the Cl- secretory process, the effect of prostaglandin E1 on ion fluxes was tested in the presence of putative inhibitors. Bumetanide was used as an inhibitor for the basolaterally localized Na+,K+,Cl- cotransport system whose existence and bumetanide sensitivity have been verified in earlier studies (Dharmsathaphorn et al. 1984. J. Clin. Invest. 75:462-471). Barium was used as an inhibitor for the K+ efflux pathway on the basolateral membrane whose existence and barium sensitivity were demonstrated in this study by preloading the monolayers with 86Rb+ (as a tracer for K+) and simultaneously measuring 86Rb+ efflux into both serosal and mucosal reservoirs. Both bumetanide and barium inhibited the net chloride secretion induced by prostaglandin E1 suggesting the involvement of the Na+,K+,Cl- cotransport and a K+ efflux pathways on the basolateral membrane in the Cl- secretory process. The activation of another Cl- transport pathway on the apical membrane by prostaglandin E1 was suggested by Cl- uptake studies. Our findings indicate that the prostaglandin E1-stimulated Cl- secretion, which is associated with an increase in cyclic AMP level, intimately involves (a) a bumetanide-sensitive Na+,K+,Cl- cotransport pathway that serves as a Cl- uptake step across the basolateral membrane, (b) the stimulation of a barium-sensitive K+ efflux mechanism on the basolateral membrane that most likely acts to recycle K+, and (c) the activation of a Cl- transport pathway on the apical membrane that serves as a Cl- exit pathway.
mesh_terms: D000527:Alprostadil / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000873:Anthracenes / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology; D002034:Bumetanide / Q000494:pharmacology; D002451:Cell Compartmentation; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D000242:Cyclic AMP / Q000096:biosynthesis; D004848:Epithelium / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism
chemical_list: D000873:Anthracenes; D002712:Chlorides; D002034:Bumetanide; D001464:Barium; C010030:9-anthroic acid; D000242:Cyclic AMP; D000527:Alprostadil; D011188:Potassium