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Inhibition of oxidative stress produced by plasma membrane NADH oxidase delays low‐potassium‐induced apoptosis of cerebellar granule cells

From 1 to 3 h after the onset of cerebellar granule cells (CGC) apoptosis in a low‐K+(5 mm KCl) medium there was a large decay of NADH and a 2.5‐fold increase of the rate of reactive oxygen species (ROS) production (measured using CGC loaded with dichlorodihydrofluorescein). During the same time period, the ascorbate‐dependent NADH oxidase activity, which accounted for more than 90% of both total NADH oxidase activity and NADH‐dependent ·O2– production of CGC lysates, increased 2.5‐ to threefold. The stimulation of the ascorbate‐dependent NADH oxidase activity by oxidized cytochrome c, 2.5‐fold at saturation with a K0.5 of 4–5 µm cytochrome c, can at least partially explain this activation. The plasma membrane ascorbate‐dependent NADH oxidase activity accounted for more than 70% of the total activity (both in terms of NADH oxidase and ·O2– release) of CGC lysates. 4‐Hydroxyquinazoline (4‐HQ), which was found to block this apoptotic process, prevented the increase of ROS production. 4‐HQ protection against cell viability loss and DNA fragmentation correlated with the inhibition by 4‐HQ of the ascorbate‐dependent NADH oxidase activity of CGC lysates, showing the same K0.5‐value (4–5 mm 4‐HQ). The efficient blockade of CGC apoptosis by addition of superoxide dismutase to the medium further supports the neurotoxic role of ·O2– overproduction by the plasma membrane ascorbate‐dependent NADH oxidase.