Reoxygenation increases the release of reactive oxygen intermediates in murine microglia

Respiratory burst activity of murine microglial cells was investigated in vitro under normoxic and hypoxic conditions with a chemoluminometric assay. Hypoxia for 24 hours reduced the release of extracellular reactive oxygen intermediates (ROIs), whereas reoxygenation increased the chemoluminescence more than sevenfold. Blockade of potassium channels inhibited the increase of oxidative burst after reoxygenation, indicating that potassium ions, which were increased in the supernatant of hypoxic microglial cells, were involved in this activation process. Also, blockade of voltage-gated calcium channels with nifedipine attenuated the increased release of ROIs. With fura-2 analysis, it was shown that the activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase by potassium ions was mediated by calcium influx via voltage-gated calcium channels. Thus, influx of calcium ions through voltage-gated channels activates the NADPH oxidase in microglial cells during reoxygenation. By the increased production of ROIs, microglial cells may add to the reperfusion injury after ischemia in vivo.