Su1135 SODIUM CAPRATE INCREASES BICARBONATE SECRETION VIA TRPV4, ATP-P2Y AND VIP-VPAC1 PATHWAYS IN RAT DUODENUM (original) (raw)

Background and Aims: Although cAMP signaling is well known to regulate epithelial ion transports, the role of Ca 2+ signaling in cAMP-mediated ion secretion is poorly understood. We aimed to investigate the role Ca 2+ signaling in cAMP-mediated intestinal epithelial ion secretion and the cross-talk mechanisms between these two signaling. Methods: Functional, biochemical and immunofluoresence techniques were performed to examine anion secretion and protein expression and localization in mouse duodenal epithelium. Results: Activation of adenaly cyclase by foskolin (10 uM) to raise intracellular cAMP or direct application of dibuty-cAMP (300 uM), a well-known cell-permeable cAMP analogy, stimulated mouse duodenal I sc when added to serosal side but not mucosal side (p<0.001, n=7). Surprisingly, cAMP-mediated intestinal I sc was significantly reduced by external Ca 2+ omission at serosal side of the tissues (p<0.01, n=6), and was inhibited by several selective blockers of storeoperated Ca 2+ channels (SOC) and CRAC/Orai channels at serosal side but not at the mucosal side (p<0.01, n=6). The ER Ca 2+ chelation by TPEN could also significantly reduced cAMPmediated intestinal I sc (p<0.001, n=6). cAMP-mediated intestinal I sc was promoted by activator of ryanodine receptor on the ER (1 mM caffeine, p<0.01, n=6), but reduced by its blocker (300 uM dantrolene, p<0.01, n=6). Furthermore, cAMP-mediated intestinal I sc was reduced by serosal addition but not mucosal addition of H-89 (20 uM, p<0.001, n=6), a PKA inhibitor. Finally, STIM1/Orai1 proteins, the molecular components of SOC, were identified on serosal side of mouse duodenal epithelium. Conclusion: Forskolin/cAMP induces intestinal ion secretion in a polarized manner. It may trigger SOC via PKA phosphrylation of ryanodine receptor to deplete the ER Ca 2+ store and cause Ca 2+ entry via STIM1/ Orai1, which plays a critical role in cAMP-mediated intestinal ion secretion. Our findings provide a new insight to a cross-talk mechanism of cAMP and Ca 2+ signaling in epithelial ion secretion.