Cells, electrochemical stimulation

Figure 21 AMPH exposure decreases the quantal amplitude of individual release events from PC 12 cells. Randomly chosen amperometric electrochemical records of quantal release for (A) a control cell and (B) a cell that has been incubated in 10 i,M d-AMPH for 10 min. Cells were stimulated by local perfusion (30 nL of 1 mM nicotine in 105 mM KCl saline) to induce vesicular exocytosis. (C) A histogram displaying the percentage of peak sizes in paired control and AMPH-treated cells. Peaks are combined in intervals of 30,000 molecules. The lower limit of each bin size is shown on the abscissa. All data were obtained using a 5 pm carbon fiber electrode held at 0.65 V vs. SSCE. (Reproduced from J. Neu-rosci. with permission [52].)...

When the nerve cell is stimulated, certain channels in the membrane open, allowing Na" ions to rush into the cell and causing the potential to temporarily rise to about +30 mV (Figure 18.13 t). Other channels that allow K ions to rush out of the cell open in turn, bringing the potential back down to near its resting potential. The result is a spike in the electrochemical potential across the membrane, which provides the... 

A FIGURE 18.14 Potential Changes across the Nerve Cell Membrane The changes in ion concentrations that take place when a nerve cell is stimulated result in a spike in the electrochemical potential across the membrane. 

When the electrical signal reaches the end of the nerve cell, it triggers the release of a chemical neurotransmitter, which travels to the neighboring nerve cell and stimulates the same kind of electrochemical spike. In this way, neural signals travel throughout the brain and nervous system. 

Electrical conductivity is of interest in corrosion processes in cell formation (see Section 2.2.4.2), in stray currents, and in electrochemical protection methods. Conductivity is increased by dissolved salts even though they do not take part in the corrosion process. Similarly, the corrosion rate of carbon steels in brine, which is influenced by oxygen content according to Eq. (2-9), is not affected by the salt concentration [4]. Nevertheless, dissolved salts have a strong indirect influence on many local corrosion processes. For instance, chloride ions that accumulate at local anodes can stimulate dissolution of iron and prevent the formation of a film. Alkali ions are usually regarded as completely harmless, but as counterions to OH ions in cathodic regions, they result in very high pH values and aid formation of films (see Section 2.2.4.2 and Chapter 4). 

C. Privat, O. Stepien, M. David-Dufilho, A. Brunet, F. Bedioui, P. Marche, J. Devynck, and M.-A. Devynck, Superoxide release from interleukin-1 (3-stimulated human vascular cells in situ electrochemical measurement. Free Radicals Bio. Med. 27, 554-559 (1999). 

A term used to describe how easily a metal is oxidized is active. A more active metal is one that is more easily oxidized. A listing of metals in order of activity is known as an activity series. The activity series is used to determine which substances will be oxidized and reduced in an electrochemical cell the element higher on the list will be oxidized. For example, in a cell with aluminum and silver electrodes in their appropriate solutions, aluminum is oxidized and silver is reduced. Therefore, aluminum is the anode and silver is the cathode. If you have ever bitten a piece of aluminum foil and experienced discomfort, you had this electrochemical process occur in your mouth. Silver (or mercury) fillings and the aluminum serve as electrodes and your saliva serves as an electrolyte between the two. The resulting current stimulates the nerves in your mouth resulting in the discomfort. 

To compare quantitatively the current-voltage characteristic of an illuminated electrode, given by formula (31), with experimental data, Butler (1977) and Wilson (1977) measured the photocurrent, which arises in a cell with an n-type semiconductor photoanode ( 2, W03) when irradiated with monochromatic light at a frequency satisfying the condition ha>> Eg. In this case a light-stimulated electrochemical reaction of water oxidation with oxygen evolution... 

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