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 > ATP gamma S > ADP beta S, whereas the P2XR agonist, methylene-adenosine-5'-triphosphate, was ineffective. Adenosine-5'-O-3-thiotriphosphate (ATPyS; 100 mu mol/L) also prevented Na+-overload in hypoxic cells by inhibiting the Na+/H+ exchanger, without interfering with hypoxic acidosis. ATPyS activated Src and promoted a Src-dependent stimulation of both ERK1/2 and p38MAPK. Blocking p38NIAPK with SB203580 reverted the protection given by ATPyS 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 ATP gamma S reverted ERK1/2 activation in hypoxic cells. SB203580 blocked the effects of ATP gamma S on both ERK1/2 and Na+/H+ exchanger. Conclusions:The activation of p38MAPK by P2Y(2)R increases hepatocyte resistance to hypoxia by down-modulating ERK1/2-mediated signals that promote Na+ influx through the Na+/H+ exchanger. (c) 2006 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.