Inositol 1,4,5-trisphosphate receptor type II (InsP3R-II) is reduced in obese mice, but metabolic homeostasis is preserved in mice lacking InsP3R-II.

Inositol 1,4,5-trisphosphate receptor type II (InsP3R-II) is the most prevalent isoform of the InsP3R in hepatocytes and is concentrated under the canalicular membrane, where it plays an important role in bile secretion. We hypothesized that altered calcium (Ca(2+)) signaling may be involved in metabolic dysfunction, as InsP3R-mediated Ca(2+) signals have been implicated in the regulation of hepatic glucose homeostasis. Here, we find that InsP3R-II, but not InsP3R-I, is reduced in the livers of obese mice.

Type 2 inositol 1,4,5-trisphosphate receptor modulates bile salt export pump activity in rat hepatocytes.

Unlabelled: Bile salt secretion is mediated primarily by the bile salt export pump (Bsep), a transporter on the canalicular membrane of the hepatocyte. However, little is known about the short-term regulation of Bsep activity. Ca(2+) regulates targeting and insertion of transporters in many cell systems, and Ca(2+) release near the canalicular membrane is mediated by the type II inositol 1,4,5-trisphosphate receptor (InsP3R2), so we investigated the possible role of InsP3R2 in modulating Bsep activity.

Prevention of liver fibrosis by the purinoceptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (PPADS).

Background: Hepatic stellate cells (HSC) are important mediators of liver fibrosis. HSC express purinergic receptors for extracellular ATP that induce fibrogenesis. Pyridoxal-phosphate-6-azophenyl-2', 4'-disulfonate (PPADS) is a highly bioavailable purinoceptor inhibitor.

Succinate is a paracrine signal for liver damage.

Background/aims: A G-protein-coupled succinate receptor has recently been identified in several tissues, including the liver. The objectives of this work were to determine the hepatic cell types that express this receptor and to determine its physiological role.

Methods: Expression and distribution of the succinate receptor was determined by RT-PCR and confocal immunofluorescence.

The spatial distribution of inositol 1,4,5-trisphosphate receptor isoforms shapes Ca2+ waves.

Cytosolic Ca(2+) is a versatile second messenger that can regulate multiple cellular processes simultaneously. This is accomplished in part through Ca(2+) waves and other spatial patterns of Ca(2+) signals. To investigate the mechanism responsible for the formation of Ca(2+) waves, we examined the role of inositol 1,4,5-trisphosphate receptor (InsP3R) isoforms in Ca(2+) wave formation.

Molecular basis for calcium signaling in hepatic stellate cells.

Progressive liver fibrosis (with the resultant cirrhosis) is the primary cause of chronic liver failure. Hepatic stellate cells (HSCs) are critically important mediators of liver fibrosis. In the healthy liver, HSCs are quiescent lipid-storing cells limited to the perisinusoidal endothelium.

Adenosine inhibits cytosolic calcium signals and chemotaxis in hepatic stellate cells.

Adenosine is produced during cellular hypoxia and apoptosis, resulting in elevated tissue levels at sites of injury. Adenosine is also known to regulate a number of cellular responses to injury, but its role in hepatic stellate cell (HSC) biology and liver fibrosis is poorly understood. We tested the effect of adenosine on the cytosolic Ca2+ concentration, chemotaxis, and upregulation of activation markers in HSCs.

Secretion of MCP-1/CCL2 by bile duct epithelia induces myofibroblastic transdifferentiation of portal fibroblasts.

Portal fibroblasts (PF) are fibrogenic liver cells distinct from hepatic stellate cells (HSC). Recent evidence suggests that PF may be important mediators of biliary fibrosis and cirrhosis. The cytokine monocyte chemoattractant protein-1 (MCP-1)/CCL2 is upregulated in biliary fibrosis by bile duct epithelia (BDE) and induces functional responses in HSC.

Protein 4.1N does not interact with the inositol 1,4,5-trisphosphate receptor in an epithelial cell line.

Cytosolic Ca2+ regulates a variety of cell functions, and the spatial patterns of Ca2+ signals are responsible in part for the versatility of this second messenger. The subcellular distribution of the inositol 1,4,5-trisphosphate receptor (IP3R) is thought to regulate Ca2+-signaling patterns but little is known about how the distribution of the IP3R itself is regulated. Here we examined the relationship between the IP3R and the cytoskeletal linker protein 4.

The anti-apoptotic protein Mcl-1 inhibits mitochondrial Ca2+ signals.

Apoptosis contributes to the regulation of cell growth and regeneration and to the development of neoplasia. Mcl-1 is an anti-apoptotic protein that is particularly important for the development of hematological and biliary malignancies, but the mechanism of action of Mcl-1 is unknown. A number of pro- and anti-apoptotic proteins exhibit their effects by modulating Ca2+ signals, so we examined the effects of Mcl-1 on components of the Ca2+ signaling pathway that are known to regulate apoptosis.

Portal fibroblasts regulate the proliferation of bile duct epithelia via expression of NTPDase2.

Bile duct epithelia are the target of a number of "cholangiopathies" characterized by disordered bile ductular proliferation. Although mechanisms for bile ductular proliferation are unknown, recent evidence suggests that extracellular nucleotides regulate cell proliferation via activation of P2Y receptors. Portal fibroblasts may regulate bile duct epithelial P2Y receptors via expression of the ecto-nucleotidase NTPDase2.

Ectonucleotidase NTPDase2 is selectively down-regulated in biliary cirrhosis.

Background: Portal fibroblasts are newly identified, potentially fibrogenic liver cells that are distinct from hepatic stellate cells. The ectonucleotidase* nucleoside triphosphate diphosphohydrolase 2 (NTPDase2) is restricted to portal fibroblasts in the normal liver. However, the fate of NTPDase2 after bile duct ligation (BDL) is unknown.

Expression of P2Y nucleotide receptors and ectonucleotidases in quiescent and activated rat hepatic stellate cells.

Extracellular nucleotides regulate a variety of cellular activities, including proliferation of fibrogenic cells outside of the liver. However, the expression of receptors for extracellular nucleotides in hepatic stellate cells (HSC) is unknown. Thus our aims were to investigate the expression of mediators of nucleotide signaling in HSC and to determine whether extracellular nucleotides regulate HSC function.

The ecto-nucleoside triphosphate diphosphohydrolase NTPDase2/CD39L1 is expressed in a novel functional compartment within the liver.

Extracellular nucleotides regulate diverse biological functions and are important in the regulation of liver metabolism, hepatic blood flow, and bile secretion. Ecto-nucleoside triphosphate diphosphohydrolases (NTPDases) hydrolyze extracellular nucleotides and are therefore potential regulators of nucleotide-mediated signaling. To examine this, we have contrasted the structural and functional distributions of the 2 characterized membrane-bound NTPDases NTPDase1 and NTPDase2 within the rat liver.

Isolation of primary rat liver fibroblasts.

Introduction: One of the major advances in liver research in the past decade was the ability to isolate distinct liver cell populations. Although there are established methods of isolating hepatocytes, cholangiocytes, and stellate cells, before this study no technique for liver fibroblast isolation had been devised. Consequently, we developed a technique to isolate primary rat liver fibroblasts.