Molecular mechanisms of calcium signaling in the modulation of small intestinal ion transports and bicarbonate secretion

// Xin Yang 1, * , Guorong Wen 2, * , Biguang Tuo 2 , Fenglian Zhang 1 , Hanxing Wan 1 , Jialin He 1 , Shiming Yang 2 and Hui Dong 1, 3 1 Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China 2 Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, and Digestive Disease Institute of Guizhou Province, Zunyi 563003, China 3 Department of Medicine, School of Medicine, University of California, San Diego, CA 92093, USA * These authors contributed equally to this work Correspondence to: Hui Dong, email: h_uidong@163.com Shiming Yang, email: 13228686589@163.com Keywords: carbachol; Ca 2+ signaling; SOCE; duodenal epithelial ion transports Received: October 19, 2017      Accepted: December 01, 2017      Published: December 11, 2017 ABSTRACT Background and Purpose: Although Ca 2+ signaling may stimulate small intestinal ion secretion, little is known about its critical role and the molecular mechanisms of Ca 2+ -mediated biological action. Key Results: Activation of muscarinic receptors by carbachol(CCh) stimulated mouse duodenal I sc , which was significantly inhibited in Ca 2+ -free serosal solution and by several selective store-operated Ca 2+ channels(SOC) blockers added to the serosal side of duodenal tissues. Furthermore, we found that CRAC/Orai channels may represent the molecular candidate of SOC in intestinal epithelium. CCh increased intracellular Ca 2+ but not cAMP, and Ca 2+ signaling mediated duodenal Cl - and HCO 3 - secretion in wild type mice but not in CFTR knockout mice. CCh induced duodenal ion secretion and stimulated PI3K/Akt activity in duodenal epithelium, all of which were inhibited by selective PI3K inhibitors with different structures. CCh-induced Ca 2+ signaling also stimulated the phosphorylation of CFTR proteins and their trafficking to the plasma membrane of duodenal epithelial cells, which were inhibited again by selective PI3K inhibitors. Materials and Methods: Functional, biochemical and morphological experiments were performed to examine ion secretion, PI3K/Akt and CFTR activity of mouse duodenal epithelium. Ca 2+ imaging was performed on HT-29 cells. Conclusions and Implications: Ca 2+ signaling plays a critical role in intestinal ion secretion via CRAC/Orai-mediated SOCE mechanism on the serosal side of epithelium. We also demonstrated the molecular mechanisms of Ca 2+ signaling in CFTR-mediated secretion via novel PI3K/Akt pathway. Our findings suggest new perspectives for drug targets to protect the upper GI tract and control liquid homeostasis in the small intestine.