Low electrical fields

Electroporation. When bacteria are exposed to an electric field a number of physical and biochemical changes occur. The bacterial membrane becomes polarized at low electric field. When the membrane potential reaches a critical value of 200—300 mV, areas of reversible local disorganization and transient breakdown occur resulting in a permeable membrane. This results in both molecular influx and efflux. The nature of the membrane disturbance is not clearly understood but bacteria, yeast, and fungi are capable of DNA uptake (see Yeasts). This method, called electroporation, has been used to transform a variety of bacterial and yeast strains that are recalcitrant to other methods (2). Apparatus for electroporation is commercially available, and constant improvements in the design are being made. 

Fig. 2. Electron drift velocities as a function of electric field for A, GaAs and B, Si The gradual saturation of curve B is characteristic of all indirect semiconductors. Curve A is characteristic of direct gap semiconductors and at low electric fields this curve has a steeper slope which reflects the larger electron mobiUty. The peak in curve A is the point at which a substantial fraction of the electrons have gained sufficient energy to populate the indirect L minimum which has a much larger electron-effective mass than the F minimum. Above 30 kV/cm (not shown) the drift velocity in Si exceeds that in...

The standard Rodbard-Ogston-Morris-Killander [326,327] model of electrophoresis which assumes that u alua = D nlDa is obtained only for special circumstances. See also Locke and Trinh [219] for further discussion of this relationship. With low electric fields the effective mobility equals the volume fraction. However, the dispersion coefficient reduces to the effective diffusion coefficient, as determined by Ryan et al. [337], which reduces to the volume fraction at low gel concentration but is not, in general, equal to the porosity for high gel concentrations. If no electrophoresis occurs, i.e., and Mp equal zero, the results reduce to the analysis of Nozad [264]. If the electrophoretic mobility is assumed to be much larger than the diffusion coefficients, the results reduce to that given by Locke and Carbonell [218]. 

Figure 29. For the latter case, it is considered that the semiconducting re-electron systems are separated by insulating hydrocarbon spacers, resulting in alternate thin layers of organic semiconductor and insulator in these monolayer assemblies. The direct current - voltage (I - V) characteristics were mea- sured for the multilayers H2Pc(R)8 and Cu-Pc(R)8 in directions perpendicular and parallel to the film plane. In both cases, the linear I - V relationships of Ohm s law were observed at low electric field and obtained DC conductivities are summarized in Table 3. The normal conductivity (ajJ were ca. 10 13 S cm-1, while the lateral ones p//) were 3.4 x 10-7 and 9.9 x 10 7 S cm 1 for films of the metal-free and copper Pc derivatives, respectively. The former (ojJ tended to decrease slightly with increase of Figure 29. Schematical illustration of the substituent alkyl chain length,...

At low electric fields v is proportional to E and a mobility /u=er/m can be defined. The mobility of electrons and holes in bulk silicon is shown in the figure on the inner front cover of this book. 

The second term of Eqn (8.13) may be compared with Ohm s law which holds at sufficiently low electrical fields as long as the product of the potential difference per atomic distance and the elementary charge is sufficiently low compared to kT (Rickert, 1985),... 

This equation shows that at low electric fields, the escape probability is a linear function of F, and the slope-to-intercept ratio of this dependence is given by erJlk T. It is worth noting that this ratio is independent of /-q. Therefore plots of (p F)l(p 0) vs. 7 may be used to test the applicability of the presented theory to describe real systems, even if the distribution of electron thermalization distances is unknown. 

At low electric fields [0(lV/cm)] the speed (U) of the particles is directly proportional to the applied field ( ) and hence we can define a parameter called the electromobility ( x) of the particles, given by U/E. Using the Poisson-Boltzmann theory of the diffuse electrical layer next to a charged surface, a simple relationship between p and V /o can be... 

Deviations from Ohm s Law are found at relatively low electric fields. 

One of the fluids was pure Mazola corn oil and the other was the same oil colored with oil-based Teal dye and doped with oil-miscible antistatic Stadis 450 to increase the conductivity and permittivity [91]. The latter values were measured with a broadband dielectric spectrometer in a spatially uniform low electric field for frequencies of 0.5-1 kHz. 

At low electrical field, Eq. (8) can be linearized, and thus an ohmic behavior is obtained ... 

Key Words Pulsed low electric fields Endocytosis Uptake kinetics Membrane internalization Albumin Lucifer Yellow Propidium iodide Adsorption Flow cytometry Confocal microscopy. 

We have introduced a novel method to enhance the uptake of macromolecules via stimulating endocytic-like processes by exposing cells to a train of pulsed low electric field, LEF (14-16). The enhanced uptake is attributed both to the direct stimulation of different endocytic pathways as well as to the indirect effect mediated through the increase of the adsorption of the macromolecules onto the exposed cells. This method has found an application in the treatment of different metastatic tumor models (17-20). 

Fig. 1. Schematic representation of a chamber, for exposure of cell suspensions to low electric field. Two stainless steel electrodes separated by a 5-mm Teflon spacer are introduced into a 1-cm plastic cuvette.

Rosenberg, Y. and Korenstein, R. (1997) Incorporation of macromolecules into cells and vesicles by low electric fields induction of endocytosis-like processes. Bioelectrochem. Bioenerg. 42, 275-281. 

Antov, Y. Barbul, A. and Korenstein, R. (2004) Electroendocytosis stimulation of adsorptive and fluid-phase uptake by pulsed low electric fields. Exp. Cell Res. 297, 348-362. 

Entin, I., Plotnikov, A., Korenstein, R. and Keisari, Y. (2003) Tumor growth retardation, cure and induction of antitumor immunity in B16 melanoma bearing mice by low electric field enhanced chemotherapy. Clin. Cancer Res. 9, 3190-3197. 

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