Expression and regulation of gap junctions in rat cholangiocytes

Cholestasis shuts down calcium signaling in cholangiocytes

BACKGROUND & AIMS

Cholestasis is one of the principal manifestations of liver disease and often results from disorders involving bile duct epithelia rather than hepatocytes. A range of disorders affects biliary epithelia, and no unifying pathophysiologic event in these cells has been identified as the cause of cholestasis. Here we examined the role of the inositol 1,4,5-trisphosphate receptor (InsP3R)/Ca(2+) release channel in Ca(2+) signaling and ductular secretion in animal models of cholestasis and in patients with cholestatic disorders.

METHODS

The expression and distribution of the InsP3R and related proteins were examined in rat cholangiocytes before and after bile duct ligation or treatment with endotoxin. Ca(2+) signaling was examined in isolated bile ducts from these animals, whereas ductular bicarbonate secretion was examined in isolated perfused livers. Confocal immunofluorescence was used to examine cholangiocyte InsP3R expression in human liver biopsy specimens.

RESULTS

Expression of the InsP3R was selectively lost from biliary epithelia after bile duct ligation or endotoxin treatment. As a result, Ca(2+) signaling and Ca(2+)-mediated bicarbonate secretion were lost as well, although other components of the Ca(2+) signaling pathway and adenosine 3',5'-cyclic monophosphate (cAMP)-mediated bicarbonate secretion both were preserved. Examination of human liver biopsy specimens showed that InsP3Rs also were lost from bile duct epithelia in a range of human cholestatic disorders, although InsP3R expression was intact in noncholestatic liver disease.

CONCLUSIONS

InsP3R-mediated Ca(2+) signaling in bile duct epithelia appears to be important for normal bile secretion in the liver, and loss of InsP3Rs may be a final common pathway for cholestasis.

Cholangiocyte biology

Cholangiocytes are of considerable intrinsic biologic interest, particularly with regard to their roles in the transport of water, ions, and solutes, and to their heterogeneity and proliferative capacity. Cholangiocytes represent an important target of study in the cholangiopathies, a group of genetic developmental and acquired diseases of the liver. New biologic concepts continue to evolve through the use of experimental models (eg, knockout mice and selective gene silencing) and enhanced approaches to three-dimensional modeling and microscopy. The role of the cholangiocyte cytoskeleton in transport and intracellular trafficking has been recently recognized. These paradigms provide a framework for further understanding the mechanisms modulating normal cholangiocyte growth, transport, and signaling, and the abnormalities that result in disease.