Platinized carbon micro electrodes {-10 (tm diameter), positioned close {~ 5 urn) to the cell membrane of a human fibroblast, the ensemble constituting a semi-artificial synapse, are used to monitor events at the cellular level. A few tens of femlomoles of reactive oxygen species produced and emitted by the cell upon mechanical pricking with a glass micropipette (~ Î um diameter) are released into the liquid film of some hundred femtoliires comprised between the cytoplasmic membrane and the

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... trode surface, leading to a sudden and drastic rise in their concentrations {in the order of several micromoles). This oxidative stress-type response aims at disarming the aggressor and is thought to be shared by many {if not all) eukaryotic cells. This method allows to detect in real time and quantify the species constituting the oxidative burst cocktail: hydrogen peroxide, H2Oj, peroxynitrite, ON02, nitrogen monoxide, N0°, and nitrite, N02. They are likely to derive ultimately from superoxide anion, 02°, and nitrogen monoxide, NO*, synthesised by NADPH oxidase and NO synthase enzyme systems, respectively. By placing the mic reelect rode at different positions about the injured area of the cell membrane, it was concluded that the signals correspond to a spherical diffusion of the emitted electroactive species from a point-source.