The role of a purinergic P 2z receptor in calcium‐dependent cell killing of isolated rat hepatocytes by extracellular adenosine triphosphate

Extracellular adenosine triphosphate (ATP o ) (0.4 mmol/L), a P 2 ‐purinergic receptor agonist, induces cytolysis in several cell types including isolated rat hepatocytes. In this study, we investigated the P 2 ‐receptor involved in ATP o ‐induced, Ca 2+ ‐dependent cytotoxicity in hepatocytes. Pretreatment of hepatocytes with oxidized ATP, a P 2z ‐receptor antagonist, or complexation of ATP 4− (the agonist for the P 2z ‐receptor) with an excess of Mg 2+ , prevented ATP o ‐induced cell death. Both protective treatments also prevented the development of a sustained high intracellular Ca 2+ concentration as well as the subsequent accumulation of inorganic phosphate (Pi). The P 2z ‐receptor agonist 3′‐O‐'(4‐benzoylbenzoyl)‐ATP (BzATP) was twofold more potent than ATP in eliciting cytolysis, which was preceded by a sustained high intracellular Ca 2+ concentration; pretreatment with oxidized ATP prevented both the increase in the intracellular Ca 2+ concentration and cell death. Prevention of ATP o ‐induced cell death, as well as the increases in the intracellular Ca 2+ concentration and inorganic phosphate (Pi) was also achieved by decreasing the pH o to 6.9. Together the findings indicate that Ca 2+ ‐dependent cell killing by extracellular ATP in hepatocytes is mediated by a P 2z ‐receptor. The cytolytic effects correlated specifically with a secondary “late” increase in the intracellular Ca 2+ concentration.