Control by Electric Field

While perhaps overly schematic, this approach proved useful for two reasons first, because it provided terminology in which one can discuss the specific structural features of ionic channels, and second, because it allowed certain qualitative predictions to be made. Thus according to the scheme it is altogether clear that there must exist an electric transmembrane current due to displacement of the charged intramembrane particles in response to a field variation. This current has received the name of gating current, the origin of which is obvious in the model in question. 

It is quite clear that any information about the motion of the gating particles would be valuable toward understanding the functioning of ion channels and the first attempts to measure gating currents were made long ago, although the insufficiency of the measurement techniques at that time rendered these unsuccessful. 

The first scientists to measure what were by all evidence gating currents were Armstrong and Bezanilla they used the squid axon. Very soon afterwards their results were corroborated by Keynes and Rojas and their publiation was succeeded by a large number of reports on gating current measurements for different systems. By now, there are several very comprehensive state-if-the-art reviews on the subject. In this section we will only touch upon the fundamental aspects of the gating current problem, not setting ourselves the task of a comprehensive exposition and appraisal of the role of this or that school or laboratory—some debatable issues are discussed, for example, in Reference (81). 

The current is carried by the intramembrane particles. This is indicated by the equality of charges carried by the asymmetric current with the voltage stimulus on and off. 

The asymmetric current has practically exponential kinetics, the time constant depending on the voltage at the depolarizing stage almost in the same manner as T (p). 

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Figure 15.4 Attachment and detachment of ferrocene nanotubes on the (3-CD SAMs/Au substrates controlled by electric fields.8 (Reprinted with permission from Y. F. Chen et al., Langmuir, 2004, 20, 8409-8413. Copyright 2004 American Chemical Society.)...

We have given perhaps undue attention to the mobile carrier mechanism because at one time it was assumed that the Na and K transport in excitable cell membranes occurred precisely via this mechanism. In 1965, Chandler and Meves undertook an experiment to assess the aforementioned specifics of the high-frequency conductance. A nerve fiber was placed in a solution containing no Na or K ions. This precluded direct current through the membrane. However, if there had been any mobile charged carriers in the membrane, the authors would have detected current on application of a variable field. The authors did not observe a detectable current under these conditions, from which it could be deduced that the transport systems of excitable membrane are structured as ion channels whose conductance is controlled by electric field. 

With these policies described above, we selected materials to build deformable machines. Prom among variety of actively deformable materials, we selected electroactive pol3rmer gel, Poly (2-acrylamido-2-methylpropane sulfonic acid) gel (PAMPS gel) [61, 128] which is capable of large deformations although the response speed is not so fast. The main advantage of this material is that transformation can be halted if required. In order to remove the effects of wires and to focus on the major problems, gel robots were controlled by electric fields. 

E GaAs(llO) Kelvin control by electric field induced... 

In the present study, our attention has been focused on cell growth direction and its vectorial control by electric fields. The effects were investigated on a single cell with a microelectrode. The use of microelectrodes may be advantageous to focus the electric field on a cell and to emphasize the vectorial property. 

From the standpoint of synchronization, cdc mutants strains are much more useful than HU treated cells for the assignment of critical point when budding direction should be determined. At first we used cdc 35 which can be arrested at the farthest point from the budding. From the result as shown in Table 1, it is concluded that the budding direction may be controlled by electric field after SPBSF, which suggests the critical point should exist after SPBSF. 

Systems that develop contractile forces are very intriguing as analogues of physiological muscles. The idea for gel muscles was based upon the work of Katchalsky and Kuhn. They have prepared polyelectrolyte films or fibers which become elongated or contracted in response to a change in pH of the surrounding solution, and have estimated the induced force and response time. The contraction of gel fibers is also achieved by electric fields. Use of electric fields has the merit that the signals are easily controlled. 

The studies presented here along with helical bundle approaches provide a vehicle for exploring in detail the structure-function relationships of ion channels through the synthesis of artificial molecules with simple and controllable structural features. The control of electric fields at the ion-selective filter may elucidate the molecular mechanism of K /Na and NaflCa selectivities. Variation of the critical pore size by synthetic elaboration may give direct clues on the magnitude of conductance and discrimination of metal ions. Further studies on voltage depend-... 

As far as man is concerned, a presynaptic inhibition of the noradrenaline release by H3 receptors was only studied in the isolated human saphenous vein In this tissue, these receptors, similarly to a2-adrenoceptors, decrease the 3H-noradrenaline overflow elicited by electrical field stimulation (Molderings et al., 1992). Therefore, the role of histamine H3-receptors in the global control of the blood pressure in humans cannot be stated at present. 

Olszowka V, Kuntermann V, Boker A (2008) Control of orientational order in block copolymer thin films by electric fields a combinatorial approach. Macromolecules 41 5515-5518... 

In contrast, noradrenergic sympathetic innervation of the airways is sparse, and these fibers do not appear to play a major role in controlling airway diameter. Bronchodilation may be brought about by nonadrenergic, noncholinergic nerves releasing nitric oxide since nitric oxide synthase inhibitors have been shown to reduce bronchodilation produced by electrical field stimulation in vitro. 

Figure 5 Inhibitory effect of SR 120819A on the electrically stimulated rabbit vas deferens. Cumulative concentration-response curves for [Leu31,Pro34]NPY on the amplitude of twitch contractions elicited by electrical field stimulation were established in the absence ( ) or in the presence of 0.1 (A), 0.3 ( ) and 1 (T) p.M of SR 120819A. Results are expressed as a percentage of the twitch control responses measured after 45 min incubation with or without SR 120819A, and are the mean SEM of 5-6 experiments.

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