Electric parameters, cell membranes

A parameter (usually symbolized by P, and often containing a subscript to indicate the specific ion) that is a measure of the ease with which an ion can cross a unit area of membrane by simple (or passive) diffusion through a membrane experiencing a 1.0 M concentration gradient. For a particular biological membrane, the permeabilities are dependent on the concentration and activity of various channel or transporter proteins. In an electrically active cell (e.g., a neuron), increasing the permeability of K+ or CF will usually result in hyperpolarization of the membrane. Increasing will cause depolarization. 

Because of the nature of electroporation, virtually any molecule can be introduced into cells. For transfer of DNA, the electroporation forces are important. An electrophoretic effect of the field causes the polyanion DNA to travel toward the positive electrode. Fluorescence studies have shown that DNA enters the cell through the pole facing the negative electrode, where the membrane is more destabilized and where the field will drive the DNA towards the center of the cell (245). Membrane resealing occurs after pore formation. Whereas pore formation happens in the microsecond time frame, membrane resealing happens over a range of minutes with variations depending on electrical parameters and temperature (246). 

Marszalek, P. Zielinsky, J. J. Fikus, M. Tsong, T. Y. Determination of electric parameters of cell membranes by a dielectrophoresis method. Biophys. J. 59, 982-987. 

The electrical parameters of varieties supplied with a liquid solution are lower than those of the varieties supplied with gases, but research in direct methanol fuel cells was done mainly with liquid supply. This type of fuel cell is much simpler to design and operate, inasmuch as neither a special evaporator nor dual temperature control (for the evaporator and for the reaction zone of the fuel cell) is needed. With the supply of a liquid methanol solution, all risk of the membrane drying out close to the anode side is eliminated. The elimination of heat is also easier with cells having liquid solution supply. All subsequent information on direct methanol fuel cells in the present chapter refers to the variety supplied with liquid water-methanol solution. 

The permeability of a cell membrane can be transiently increased when a micro-milUsecond external electric field pulse is applied on a ceU suspension [1-4]. Under suitable conditions depending mainly on the pulse parameters (field strength, pulse duration, number of pulses), the viability of the cell can be preserved. The resulting electropermeabilization is a powerful electrochemical tool to gain access to the cytoplasm and to introduce chosen foreign molecules or to extract metabolites [5-10]. 

Table II gives a summary of the late proximal tubule activity ratios, electrical PDs and calculated equilibrium potentials. These parameters are presented under three headings (1) across the tubular epithelium (transepithelial), (2) across the luminal cell membrane (luminal), and (3) across the peritubular cell membrane (peritubular). Whereas the transepithelial treatment is essentially one that deals with a two-compartment system, analysis across the luminal and peritubular boundaries involves a three-compartment system.

Automatic Aa The 0 point for this parameter is calculated relative to the mean electrical resistance of cell membranes or their permeability (electrochemical gradient of diffusion and activity). This will demonstrate the relationship between electrical membrane conductivity and ionic concentration of the interstitium ... 

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