STORE OPERATED Ca2+ CHANNELS IN LIVER CELLS: REGULATION BY BILE ACIDS AND A SUB-REGION OF THE ENDOPLASMIC RETICULUM

Author: Joel Castro Kraftchenko

Castro Kraftchenko, Joel, 2008 STORE OPERATED Ca2+ CHANNELS IN LIVER CELLS: REGULATION BY BILE ACIDS AND A SUB-REGION OF THE ENDOPLASMIC RETICULUM, Flinders University, School of Medicine

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Abstract

Cholestasis is an important liver pathology. During cholestasis bile acids accumulate in the bile canaliculus affecting hepatocyte viability. The actions of bile acids require changes in the release of Ca2+ from intracellular stores and in Ca2+ entry. The target(s) of the Ca2+ entry pathway affected by bile acids is, however, not known. The overall objective of the work described in this thesis was to elucidate the target(s) and mechanism(s) of bile acids-induced modulation of hepatocytes calcium homeostasis. First, it was shown that a 12 h pre-incubation with cholestatic bile acids (to mimic cholestasis conditions) induced the inhibition of Ca2+ entry through store-operated Ca2+ channels (SOCs), while the addition of choleretic bile acids to the incubation medium caused the reversible activation of Ca2+ entry through SOCs. Moreover, it was shown that incubation of liver cells with choleretic bile acids counteracts the inhibition of Ca2+ entry caused by pre-incubation with cholestatic bile acids. Thus, it was concluded that SOCs are the target of bile acids action in liver cells. Surprisingly, despite the effect of choleretic bile acids in activating SOCs, the Ca2+ dye fura-2 failed to detect choleretic bile acid-induced Ca2+ release from intracellular stores in the absence of extracellular Ca2+. However, under the same conditions, when the sub-plasma membrane Ca2+ levels were measured using FFP-18 Ca2+ dye, choleretic bile acid induced a transient increase in FFP-18 fluorescence. This evidence suggested that choleretic bile acids-induced activation of Ca2+ entry through SOCs, involving the release of Ca2+ from a region of the endoplasmic reticulum (ER) located in the vicinity of the plasma membrane.

Keywords: Liver cells,Store Operated Calcium Channels,Bile Acids,Endoplasmic Reticulum,STIM1,Orai1,TRPV1,Fura-2
Subject: Medicine thesis, Medical Biochemistry thesis

Thesis type: Doctor of Philosophy
Completed: 2008
School: School of Medicine
Supervisor: Professor Greg Barritt