Short communicationImportance of the non-selective cation channel TRPV1 for microglial reactive oxygen species generation
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.
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