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.