33 Similar to previous studies,34 we propose that changes in the biliary microenvironment may partly explain the effect of GABA on small and large cholangiocytes. Another interesting aspect to consider regards the possible role of GABA receptor antagonists in experimental models and human pathologies. When the liver of BDL rats is deprived of cholinergic (by vagotomy) or adrenergic (by 6-hydroxydopamine) innervation, large cholangiocytes lose their response to cholestasis and undergo apoptosis, reducing cAMP levels and the choleretic response to secretin.35, 36 The damage and loss of

proliferative and secretory functions of cholangiocytes, by vagotomy and 6-OHDA, is prevented by the administration of forskolin, and β1-/β2-adrenergic receptor agonists.35,

36 Because GABA concomitantly damages selleckchem large cholangiocytes and induces ductular reaction, we speculate that the administration of GABA receptor antagonists may prevent the damage of large cholangiocytes (sustaining large biliary proliferation and secretion) in the denervated liver. This may be important for the homeostasis of the transplanted (denervated) liver, where ischemic or infectious insults against intrahepatic bile ducts may not be adequately counteracted during the immediate post-transplant period. The finding that the activation of IP3/Ca2+-dependent signaling regulates the differentiation C59 wnt in vivo of small into large cholangiocytes supports the concept that cross-talk between IP3/Ca2+ and cAMP is important in the regulation

of biliary homeostasis. For example, alpha-1 adrenergic receptor agonists stimulate secretin-stimulated choleresis of BDL rats by Ca2+- and protein kinase C (PKC)α/βII-dependent activation of cAMP signaling.37 Gastrin inhibits cAMP-dependent secretion and hyperplasia in BDL rats by activation of Ca2+-dependent PKCα.38 In support MCE公司 of our findings, activation of the Ca2+/calcineurin/NFAT2 pathway controls smooth muscle cell differentiation.39 Ca2+ ions regulate the differentiation and proliferation of human bone-marrow–derived mesenchymal stem cells.40 In this study, we have identified two signaling molecules (CaMK I and AC8) playing major roles in the differentiation of Ca2+-dependent small into large cholangiocytes. Previous studies in other cells support the concept that CaMK I regulates the expression of AC8.41 In fact, when secretion was induced by forskolin, a general stimulator of AC isoforms, except for AC9 and sAC, administration of calmodulin inhibitors and AC8 small interfering RNA did not cause a significant inhibitory effect.9 AC8 is the only known calmodulin-activated AC in cholangiocytes, whereas AC9 activity is inhibited by calmodulin.