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Importance of the non-selective cation channel TRPV1 for microglial reactive oxygen species generation

https://doi.org/10.1016/j.jneuroim.2009.07.008Get rights and content

Abstract

Activated microglial cells generate reactive oxygen species (ROS), which have detrimental effects in neuroinflammatory and neurodegenerative diseases. In the present study, we have identified a novel mechanism involved in microglial NADPH oxidase-mediated ROS production. In PMA-stimulated microglia, ROS production was substantially reduced upon inhibition of the non-selective cation channel TRPV1 with La3+, ruthenium red, capsazepine and 5-iodo-resinferatoxin. Furthermore, sustained membrane depolarization, a hallmark of NADPH oxidase activity in phagocytes, was found to induce non-selective cation/TRPV1 channel activity in microglia. Together, our data suggest that TRPV1 channels are involved in regulating NADPH oxidase-mediated ROS generation in microglia.

Introduction

Microglial activation is a hallmark of acute brain injury as well as of chronic neuroinflammatory and neurodegenerative diseases. Although activated microglial cells can have beneficial effects, such as removal of damaged brain tissue, secretion of neurotrophic factors and production of anti-inflammatory cytokines (Streit et al., 2008), growing evidence suggests that in brain pathology activated microglial cells exert detrimental effects by producing significant amounts of neurotoxic factors, including reactive oxygen species (ROS) (Block et al., 2007, Wang et al., 2007, Block, 2008, Miller et al., 2009). The mechanisms underlying microglial ROS production are not completely understood, and the involvement of a variety of ion channels has been suggested as a means to allow a counterion movement across the membrane to balance the inward current produced by the NADPH oxidase extruding electrons (Khanna et al., 2001, Eder, 2005, Thomas et al., 2007, De Simoni et al., 2008, Milton et al., 2008). The NADPH oxidase is thought to be the main source of microglial ROS in brain pathology. Because the cell membrane depolarizes to potentials of up to + 60 mV during the NADPH oxidase-mediated respiratory burst of phagocytes (Jankowski and Grinstein, 1999), we investigated in microglia whether membrane depolarization leads to the activation of ion channels and whether these channels are important for microglial ROS generation.

Section snippets

Chemicals

The following agents were used in this study: phorbol 12-myristate 13-acetate (PMA), LaCl3, ruthenium red, capsazepine, 5-iodo-resiniferatoxin (I-RTX; Tocris, UK). If not stated otherwise, drugs were obtained from Sigma.

Cell and brain slice preparations

BV-2 microglial cells were cultured as described previously (Schilling and Eder, 2004). Acute and organotypic hippocampal slices were prepared as described previously (Schilling and Eder, 2007).

Patch clamp recordings

Membrane currents were measured and analyzed as described previously (for in vitro

Results and discussion

During the respiratory burst, phagocytes undergo strong membrane depolarization (Jankowski and Grinstein, 1999). To test whether depolarization is sufficient to trigger the activity of ion channels, which might be required for charge compensation during the respiratory burst of microglial cells, we performed patch clamp experiments. Voltage ramps to potentials between − 90 and + 60 mV were applied for 300 ms every 20 s. Clamping the holding potential from − 60 mV to 0 mV or more positive values

Acknowledgements

This work was supported by German Research Foundation grant SFB 507/C7, a start-up grant from St. George's, University of London and a Wellcome Trust Value in People Award.

References (22)

  • EderC. et al.

    Properties of voltage-gated currents of microglia developed using macrophage colony-stimulating factor

    Pflügers Arch.

    (1995)
  • Cited by (0)

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