Microelectrodes in Artificial Synapses: a Study of Oxidative Stress at the Cellular Level

Abstract

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 electrode 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.

Chemical instability promotes apparent electrochemical irreversibility: Studies on the electrode kinetics of the one electron reduction of the 2,6-diphenylpyrylium cation in acetonitrile solution

“…Voltammetry of 2,6-diphenylpyrylium perchlorate on platinum at scan rates in excess of 10 5 V s À1 has been published by Amatore [23,25], in which the reverse peak has been resolved. It was noted that, due to ohmic distortions, a precise determination of k EC 2 directly from the fast-scan data was not possible, so an indirect method was used.…”

“…A diffusion coefficient of D = 1.2 ± 0.1 · 10 À5 cm 2 s À1 was established by applying the fitting methods previously described [29,30]. We are unaware of any previously published value for this constant [23][24][25]. Fig.…”

“…1) [23][24][25]. In this paper the reaction is studied at a gold tubular flow cell and the results of the numerical simulations are directly applied to interpret the measured waveshape and to determine kinetic data.…”

The linear sweep voltammetry of random arrays of microdisc electrodes: Fitting of experimental data

“…The use of single microelectrodes has revolutionised both the spatial and temporal aspects of electrochemistry, for example, allowing microscopic imaging of electrode surfaces [1][2][3] and access to hitherto inaccessible short timescales [4][5][6]. Nevertheless for many practical purposes, notably analytical measurements [7][8][9][10] and studies of metal nucleation and growth phenomena [11,12], it has proved convenient and advantageous to employ arrays containing hundreds or even thousands [13] of microdisc electrodes wired in parallel.…”

New Chemical Insights Using Weakly Supported Voltammetry: Ion Pairing in the EC2 Reduction of 2,6‐Diphenylpyrylium in Acetonitrile

“…Previous studies on this mechanism have reported surprisingly different values of k dim , from 2.5 10 7 m À1 s À1[6] to 2.5 10 9 m À1 s À1 [7,8] .…”