P2X receptors regulate adenosine diphosphate release from hepatic cells

Area of Science:

• Biochemistry
• Cell Biology
• Cancer Research

Background:

• Extracellular nucleotides, including adenosine triphosphate (ATP) and adenosine diphosphate (ADP), are crucial paracrine regulators of cellular signaling and metabolism.
• Human hepatic carcinoma cells' release and metabolism of extracellular nucleotides are key to understanding cellular responses to stress.

Purpose of the Study:

• To evaluate the release and metabolism of extracellular adenosine polyphosphates (ATP and ADP) by human hepatic carcinoma cells.
• To investigate the regulatory mechanisms of ADP release, including the role of P2X receptors and intracellular calcium.

Main Methods:

• Measurement of extracellular ATP and ADP levels in hepatic cells under various conditions (serum/glucose deprivation, ionomycin, BzATP).
• Gene silencing of purinergic receptors P2X7 and P2X4 using small interference RNA (siRNA).
• Treatment with P2X inhibitor A438079 to assess its effect on nucleotide release.

Main Results:

• Serum or glucose deprivation significantly increased extracellular ADP release (up to 10-fold) but not ATP.
• Ionomycin and BzATP stimulated nucleotide release, with BzATP causing a >100-fold increase in both ATP and ADP.
• P2X7 and P2X4 gene silencing and P2X inhibition reduced ADP release, indicating P2X receptor involvement, but did not affect ATP release or BzATP-stimulated release.

Conclusions:

• Extracellular ADP release from human hepatic carcinoma cells is primarily regulated by P2X receptors and intracellular calcium levels.
• Cellular stress, such as serum or glucose deprivation, triggers increased extracellular ADP release as part of a stress response.