Phosphatidylinositol 3-kinase is involved in prostaglandin E2-mediated murine duodenal bicarbonate secretion

Prostaglandin E-2 ( PGE(2)) plays an important role in the regulation of duodenal bicarbonate ( HCO3-) secretion, but its signaling pathway( s) are not fully understood. In the present study, we investigated the signaling pathways involved in PGE(2)- mediated duodenal HCO3- secretion. Murine duodenal mucosal HCO3- secretion was examined in vitro in Ussing chambers by pH- stat titration in the presence of a variety of signal transduction modulators. Phosphatidylinositol 3-kinase ( PI3K) activity was measured by immunoprecipitation of PI3K and ELISA, and Akt phosphorylation was measured by Western analysis with anti- phospho- Akt and anti- Akt antibodies. PGE(2)-stimulated duodenal HCO3- secretion was reduced by the cAMP- dependent signaling pathway inhibitors MDL- 12330A and KT- 5720 by 23% and 20%, respectively; the Ca2+- influx inhibitor verapamil by 26%; and the calmodulin antagonist W- 13 by 24%; whereas the PI3K inhibitors wortmannin and LY- 294002 reduced PGE(2+)-stimulated HCO3- secretion by 51% and 47%, respectively. Neither the MAPK inhibitor PD- 98059 nor the tyrosine kinase inhibitor genistein altered PGE(2)-stimulated HCO3- secretion. PGE(2) application caused a rapid and concentration- dependent increase in duodenal mucosal PI3K activity and Akt phosphorylation. These results demonstrated that PGE2 activates PI3K in duodenal mucosa and stimulates duodenal HCO3+ secretion via cAMP-, Ca-2(+)-, and PI3K-dependent signaling pathways.