Redox Modulation of ATP-Gated P2X7 Currents

Abstract

Activation of P2X7 receptors is known to initiate downstream signaling processes including the release of proinflammatory cytokines and reactive oxygen species (ROS). Recombinant and native P2X7 receptors have been observed to exhibit time-dependent changes in current amplitude, an effect observed both during prolonged continuous ATP exposure and during short repeated applications of adenosine 5′-triphosphate (ATP). We used patch clamp electrophysiology in the whole cell perforated patch configuration to test the hypothesis that this time-dependent change in current amplitude reflected changes in the redox environment of membrane P2X7 receptors. In HEK293 cells expressing recombinant P2X7 receptors, we found that short repeated applications of ATP (1 s exposure every 60 s) evoked currents that increased and/or decreased in peak amplitude for several minutes before reaching a reproducible steady state amplitude. In cells that ultimately exhibited a net reduction in peak current amplitude over time, we observed that exposure to the membrane permeable reducing agent, DTT (1 mM, 1 min), significantly increased the peak current amplitude of subsequent ATP-evoked responses. We repeated the experiment with the endogenous reducing agent, glutathione, and this chemical also potentiated the amplitude of ATP-gated currents in these cells. In all cells, exposure to the oxidizing agent, hydrogen peroxide, was observed to reduce the amplitude of ATP-gated currents. In summary, ATP-gated currents through P2X7 receptors appear to be sensitive to modulation by redox chemicals.