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First published on August 26, 2004; DOI: 10.1124/mol.104.000851

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Received for publication March 30, 2004.
Revised August 6, 2004.
Accepted for publication August 24, 2004.

SELECTIVE MODULATION OF LIGAND-GATED P2X PURINOCEPTOR CHANNELS BY HYPOXIA IS MEDIATED BY REACTIVE OXYGEN SPECIES

Helen S. Mason 1*, Steven Bourke 1, Paul J. Kemp 1

1 University of Leeds

* Address correspondence to: E-mail: h.s.mason{at}leeds.ac.uk

Abstract

Purinergic excitatory synapses use ATP to mediate fast synaptic transmission via activation of P2X receptor cation channels and this response can be altered by acute hypoxia. This study examined the effect of acute hypoxia on cloned homo- and heteromeric P2X2 and P2X3 receptors expressed in HEK293 cells. In cells expressing homomeric P2X2 receptors, perfusion of 5µM ATP (EC25) induced an inward whole-cell current that showed little desensitization during repeated exposures under continuously normoxic conditions. Exposure to an hypoxic ATP solution (PO2 25-40 mmHg) significantly reduced the whole-cell current to 49% of normoxic control. This hypoxic inhibition of P2X2-mediated inward current was maintained across all potentials when a voltage step protocol was applied. In contrast, currents mediated by homomeric P2X3 receptors or heteromeric P2X2/3 receptors were insensitive to an acute hypoxic challenge. One mechanism whereby hypoxia may modulate P2X2 channels is via the production of reactive oxygen species (ROS). H2O2 (1.8mM) reversibly reduced homomeric P2X2 whole-cell currents to 62% of control. Further, H2O2 attenuated the effect of hypoxia on homomeric P2X2 whole-cell currents. Inhibitors of the mitochondrial electron transport chain that reduce (rotenone and myxothiazol) or increase (antimycin A) the production of ROS altered the magnitude of P2X2-mediated currents. In summary, this is the first report indicating that acute hypoxia is able to regulate the activity of any ligand-gated ion channel. Furthermore, our data show that acute hypoxia selectively modulates the P2X2 receptor and that the response of P2X2 receptor subunits to hypoxia is mediated through the mitochondrial production of ROS.


Key words: Purinergic, Ion channel regulation, Mitochondrial toxins, Reactive intermediates


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