Microelectrode techniques

Ogden, D. C., Microelectrode Techniques The Plymouth Workshop Handbook, 2nd ed., The Company of Biologists, Ltd., Cambridge, U.K., 1994 (excellent discussion of both methods and principles). 

Zhang TC, Pang H. Applications of microelectrode techniques to measure pH and oxidation-reduction potential in rhizosphere. Soil Environ. Sci. Technol. 1999 33 1293-1299. 

The neurotoxic actions of T17 on membrane excitability were examined in squid giant axon initially and in more detail using crayfish giant axon and intracellular microelectrode techniques(14). Detailed studies utilizing T34 are not available due to technical problems associated with its extreme hydrophobicity and resulting diffi-... 

Fig. 7.35. Development of diffusion concentration profiles in ensembles of microelectrodes. Concentration distortions at very short times during chronoamperometry or fast sweep rates during (a) cyclic voltammetry, (b) intermediate times or sweep rates, and (c) long times or slow sweep rates. Voltam-metric responses are shown schematically. (Reprinted from B. R. Scharifker, Microelectrode Techniques in Electrochemistry, in Modem Aspects of Electrochemistry, Vd. 22, J. O M. Bockris, B. E. Conway, and R. E. White, eds., Plenum, 1992, p. 505.)...

A practical use of a microelectrode The advantages of microelectrode techniques are especially pronounced for systems with limited conductivity (e.g., polymer electrolytes), which are popular candidates for state-of-the-art lithium ion batteries, normally with room-temperature conductivities K - 10-4 S/cm. (a) A researcher is evaluating a newly synthesized lithium polymer electrolyte. He uses a two-electrode cell in which an electrolyte disk of 0.1 cm X 1.0 cm is... 

For these researchers, transients are not merely helpful but essential. Because each method has limitations, it is desirable to use two and even three transient methods for one reaction. Rotating disk and microelectrode techniques and the steady-state methods, summarized in Table 7., may be added to the armory. In the background are the developing in situ spectroscopic methods, which, if their time of operation can be made short enough,15 may eventually do some of the things the transient methods purport to achieve. For reactions with intermediates, spectroscopic methods may eventually offer more information than do transients, even though some of these are oriented to give information on intermediates. 

There are several excellent articles which deal with the theory and practice of cyclic voltammetry.1-4 Foremost among these is the comprehensive treatise by Bard and Faulkner which gives a thorough description of the theory of controlled potential microelectrode techniques, including cyclic voltammetry.1 Particularly readable accounts of cyclic voltammetry and related techniques are given in Adams book, Electrochemistry at Solid Electrodes ,2 in Pletcher s review3 and in a series of articles which appeared in J. Chem. Educ.e>... 

Cyclic voltammetric and related techniques are particularly valuable for determining Ea values in cases where one member of the redox couple is unstable. At a microelectrode in electrolytes of low resistivity, cyclic voltammograms can be recorded at scan rates up to about 100 V s-1 and at low temperatures. This allows the detection of reversibility when the unstable partner has a life-time of the order of a millisecond or so. Ultra-microelectrode techniques promise to lower this limit even further.1-3... 

Recently, both hirsutine (85) and dihydrocorynantheine (86) were found to be active when the effects of these compounds on the action potentials of sino-atrial node, atrium and ventricle tissues were studied with standard microelectrode techniques [65]. In sino-atrial node preparations, both compounds concentration-dependently increased cycle length, decreased the slope of the pacemaker depolarization, decreased the maximum rate of rise and prolonged action potential duration. Thus, it was for the first time shown that hirsutine and dihydrocorynantheine have direct inhibitory effects on the cardiac pacemaker. In atrial and ventricular preparations, both compounds concentration-dependently decreased the maximum rate of rise and prolonged action potential duration. Although stereochemically different, these two alkaloids exhibited no difference in their effects on various myocardial action potential parameters. Dihydrocorynantheine also displays potent a-adrenoceptor blocking activity, while hirsutine is inactive [66]. Experiments with ion channels indicate that the mechanisms for these two phenomena probably differ. The direct effects of hirsutine and dihydrocorynantheine on the action potential of cardiac muscle through inhibition of multiple ion channels may explain the negative chronotropic and antiarrhythmic activities of these two alkaloids. 

As discussed in Chapter 12, microelectrode techniques allow the easy determination of the rates of reaction of species with half-lives on the order of 10 ps, which can be extended in certain cases to submicrosecond half-lives. Nevertheless, it is sometimes better to lower the rate of the chemical reaction by lowering the temperature this is probably the most common motivating factor for such studies. 

Zuleta, M., Bursell, M., Bjornbom, P., and Lundblad, A. Determination of the effective diffusion coefficient of nanoporous carbon by means of a single particle microelectrode technique.. /. Electroanal. Chem. 549, 2003 101-108. 

Microelectrode techniques were applied and enabled the direct study of kinetics of the Li/Li+ couple [88,89],... 

Teramoto et al. (1997) examined the membrane potential in the proximal urethra of pigs by use of the microelectrode technique. 

Williams, A. J. In Microelectrode Techniques—The Plymouth Workshop Handbook, 2nd ed. Ogden, D., Ed. The Company of Biologists Limited Cambridge, 1994, pp. 79-101 and references cited therein. 

Kawano et al. used a microelectrode technique and the Dahms-Ruff equation to explore the diffusion mechanism of the iodide/triiodide redox couple and explain the physical diffusion accompanying an exchange reaction [22]. They showed that when high concentrations of iodide and tiiiodide are added to a RTCL as the solvent, the diffusion coefficient derived from the exchange reaction, expressed by / + —> /f + / , become significant and superior to the simple physical dif-... 

The electropharmacological effects of berberine on canine cardiac Purkinje fibers and ventricular muscle and atrial muscle, as well as rabbit atrial muscle were studied via conventional microelectrode techniques to obtain intracellular recordings of transmembrane electrical potentials. The results suggest that berberine exerts Class III antiarrhythmic and proarrhythmic actions in canine cardiac muscle in vitro [218]. 

Standard microelectrode techniques were used to study the effects of isocorydine on potential characteristics of canine cardiac Purkinje fibers and ventricular myocardium in vitro. In the Purkinje fibers, the action potential durations APDjj and APD were prolonged at 3 pmol/1 but shortened at 30 pmol/1 by isocorydine. The action potential amplitude and maximal upstroke velocity were decreased at 100 pmol/1. In the ventricular myocardium, the action potential characteristics were changed by isocorydine at concentrations above 30 pmol/1. The APDJ0 was shortened, the APD90 was prolonged, and the maximal upstroke velocity was decreased at 30 pmol/1. The effective refractory period was prolonged by the alkaloid in Purkinje fibers and ventricular myocardium. These results indicated that the alkaloid may interfere with K+, Na+, and Ca+2 currents in myocardial cell membranes at different concentrations [287]. 

A promising application of this new functionalization method of metal oxides relates to the photosensitization of semiconducting oxides to convert light into electricity. Thus, using the cavity microelectrode technique, a significant photocurrent is produced under blue light illumination by Ic- and Id-modified, F-doped and undoped Sn02 nanoporous powders, in the presence of an aqueous electrolyte, the... 

The voltammetric techniques discussed so far are microelectrode techniques. The only concentration changes considered are those occurring in the immediate vicinity of the electrode, and the effect of these microexperiments on the bulk concentration of... 

Two methods were used to study the effect of cannabinoids on presynaptic axon terminals. The more frequently used electrophysiological approach measures neurotransmission. In hrain slices or neuronal cultures, electrical currents in postsynaptic neurons are recorded with patch-clamp or microelectrode techniques. Presynaptic axon terminals are electrically stimulated and the postsynaptic current resulting from stimulation of ligand-gated ion channels of postsynaptic neurons hy the released transmitter is determined. The change in the postsynaptic current amplitude is a measure of the change in synaptic transmission. 

Microelectrode Techniques in Electrochemistry Electron Transfer Reactions on Oxide-Covered Metal Electrodes Scanning Tunneling Microscopy A Natural for Electrochemistry... 

The tip response in SECM is strongly dependent on local mass transport, and this may in fact be utilized to image local mass transport. Examples include the transport of oxygen and electroactive ions in cartilage (80), convective (81) and diffusional (34) transport in dentinal tubules, and ionic fluxes through skin (82), which are described in Chapters 9 and 12. In this section we discuss briefly experiments by Pohl, Antonenko and coworkers which, though not SECM, employ microelectrode techniques in a similar manner. 

The higher doses of OPC induced neuromuscular block. The recovery of neuromuscular transmission (NMT) is an important mechanism of antidodal action of oximes [8,9]. Smith and Muir [27] stated that this action was not connected to cholinesterase reactivation. This is in agreement with our previous work [7, 11] with microelectrode technique in vivo, as well as with the histochemical and biochemical findings, which showed prcsynaptic and postsynaptic effects of oximes in rat striated muscle after OP intoxication... 

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