Submitted on December 9, 2005
Accepted on November 1, 2006
Phosphatidylinositol 3-kinase facilitates bile acid-induced Ca2+ responses in pancreatic acinar cells
Lars Fischer1, Anna S. Gukovskaya2*, Josef M Penninger3, Olga M. Mareninova2, Helmut Friess4, Ilya Gukovsky2, and Stephen J. Pandol2
1 Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California, United States; Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States; Department of Surgery, University of Heidelberg, Heidelberg, California, Germany
2 Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California, United States; Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States
3 Institute for Molecular Biotechnology, Austrian Academy of Sciences, Vienna, California, Austria
4 Department of Surgery, University of Heidelberg, Heidelberg, California, Germany
* To whom correspondence should be addressed. E-mail: agukovsk{at}ucla.edu.
Bile acids are known to induce Ca2+ signals in pancreatic acinar cells. We recently showed that phosphatidylinositol 3-kinase (PI3K) regulates changes in free cytosolic Ca2+ ([Ca2+]i) elicited by cholecystokinin (CCK) by inhibiting sarco/endoplasmic reticulum Ca2+-ATPase (SERCA). The present study sought to determine whether PI3K regulates bile acid-induced [Ca2+]i responses. In pancreatic acinar cells, pharmacologic inhibition of PI3K with LY294002 or wortmannin inhibited [Ca2+]i responses to taurolithocholic acid 3-sulfate (TLC-S) and taurochenodeoxy-cholate (TCDC). Furthermore, genetic deletion of PI3K gamma isoform also decreased [Ca2+]i responses to bile acids. Depletion of CCK-sensitive intracellular Ca2+ pools or application of caffeine inhibited bile acid-induced [Ca2+]i signals, indicating that bile acids release Ca2+ from agonist-sensitive ER stores via IP3-dependent mechanism. The PI3K inhibitors increased the amount of Ca2+ in intracellular stores during the exposure of acinar cells to bile acids, suggesting that PI3K negatively regulates the SERCA-dependent Ca2+ reloading into ER. Bile acids inhibited Ca2+ reloading into ER in permeabilized acinar cells. This effect was augmented by phosphatidylinositol 3,4,5-trisphosphate (PIP3) suggesting that both bile acids and PI3K act synergistically to inhibit SERCA. Furthermore, inhibition of PI3K by LY294002 completely inhibited trypsinogen activation caused by TLC-S. Our results indicate that PI3K and its product, PIP3, facilitate bile acid-induced [Ca2+]i responses in pancreatic acinar cells through inhibition of SERCA-dependent Ca2+ reloading into ER and that bile acid-induced trypsinogen activation is mediated by PI3K. The findings have important implications for the mechanism of acute pancreatitis since [Ca2+]i increases and trypsinogen activation mediate key pathologic processes in this disorder.
