Purinergic P2Y₂ receptors promote hepatocyte resistance to hypoxia

Background/Aims: ATP stimulation of purinergic P2 receptors (P2YR and P2XR) regulates several hepatic functions. Here we report the involvement of ATP-mediated signals in enhancing hepatocyte tolerance to lethal stress. Methods: The protection given by purinergic agonists was investigated in rat hepatocytes exposed to hypoxia. Results: ATP released after hypotonic stress (200 mOsm/L) as well as P2YR agonists prevented hepatocyte killing by hypoxia with efficiency ranking UTP > ATPγS > ADPβS, whereas the P2XR agonist, methylene-adenosine-5′-triphosphate, was ineffective. Adenosine-5′-O-3-thiotriphosphate (ATPγS; 100 μmol/L) also prevented Na⁺-overload in hypoxic cells by inhibiting the Na⁺/H⁺ exchanger, without interfering with hypoxic acidosis. ATPγS activated Src and promoted a Src-dependent stimulation of both ERK1/2 and p38MAPK. Blocking p38MAPK with SB203580 reverted the protection given by ATPγS on both cell viability and Na⁺ accumulation, whereas ERK1/2 inhibition with PD98058 was ineffective. An increased phosphorylation of ERK1/2 was also evident in untreated hypoxic hepatocytes. PD98058 ameliorated Na⁺ accumulation and cell death caused by hypoxia. Hepatocyte pre-treatment with ATPγS reverted ERK1/2 activation in hypoxic cells. SB203580 blocked the effects of ATPγS on both ERK1/2 and Na⁺/H⁺ exchanger. Conclusions: The activation of p38MAPK by P2Y₂R increases hepatocyte resistance to hypoxia by down-modulating ERK1/2-mediated signals that promote Na⁺ influx through the Na⁺/H⁺ exchanger.