Adenosine nucleotides in bile

Area of Science:

• Hepatology
• Cell Biology
• Biochemistry

Background:

• Purinergic receptors are activated by extracellular adenosine triphosphate (ATP).
• Activation of these receptors stimulates chloride (Cl-) efflux in biliary epithelial cells.
• The physiological presence and release of purinergic agonists in bile were previously uncharacterized.

Purpose of the Study:

• To determine if purinergic agonists are present in mammalian bile under physiological conditions.
• To assess the capability of hepatoma and cholangiocarcinoma cell lines for nucleotide release.
• To investigate the potential role of local nucleotide release in modulating biliary secretion.

Main Methods:

• Nucleotide concentrations in human, rat, and pig bile were measured using luminometry.
• In vitro models of HTC rat hepatoma and Mz-ChA-1 cholangiocarcinoma cells were used to assess nucleotide release.
• The effect of 5'-nucleotidase inhibition on AMP concentrations was evaluated.
• Stimulation of nucleotide release by forskolin and ionomycin was examined in cell lines.

Main Results:

• Adenosine nucleotides (ATP, ADP, AMP) were detected in mammalian bile, with significant concentrations in human bile (average 5.21 microM).
• Both hepatoma and cholangiocarcinoma cell lines released nucleotides in vitro.
• Inhibition of 5'-nucleotidase increased AMP levels, indicating ongoing nucleotide metabolism.
• Cholangiocarcinoma cells, but not hepatoma cells, showed stimulated nucleotide release upon exposure to forskolin or ionomycin.

Conclusions:

• Mammalian bile contains adenosine nucleotides at concentrations sufficient to activate purinergic receptors.
• Local release of nucleotides from biliary cells may function as an autocrine or paracrine mechanism.
• This purinergic signaling could play a role in the regulation of biliary secretion.