Membrane potentials principles

A permeable membrane, which merely serves to prevent rapid mixing of components within solutions on both sides of the membrane in principle, no potential occurs unless a diffusion potential occurs. 

Osmosis is the passage of a pure solvent into a solution separated from it by a semipermeable membrane, which is permeable to the solvent but not to the polymeric solute. The osmotic pressure n is the pressure that must be applied to the solution in order to stop the flow. Equilibrium is reached when the chemical potential of the solvent is identical on either side of the membrane. The principle of a membrane osmometer is sketched in Figure 2. 

Figure 5.3. (a) Example for a compound used in the study of membrane potentials and (b) principle of funcboning of visualizing nerve pulses in a living cell. When a nerve pulse passes, the membrane potential changes, and this induces a change in the fluorescence intensity of the probe. The temporal and spatial profile of these changes can be followed by time-resolved methods. 

Strategies for the design of mitochondria-targeted drug and DNA delivery systems and the principles such systems are based upon have been reviewed earlier by us comprehensively (16-18). Therefore, the scope of this chapter shall be limited exclusively to approaches involving mitochondriotropic molecules-mediated drug and DNA delivery to mammalian mitochondria in response to the mitochondrial membrane potential. 

Earlier, Gavach et al. studied the superselectivity of Nafion 125 sulfonate membranes in contact with aqueous NaCl solutions using the methods of zero-current membrane potential, electrolyte desorption kinetics into pure water, co-ion and counterion selfdiffusion fluxes, co-ion fluxes under a constant current, and membrane electrical conductance. Superselectivity refers to a condition where anion transport is very small relative to cation transport. The exclusion of the anions in these systems is much greater than that as predicted by simple Donnan equilibrium theory that involves the equality of chemical potentials of cations and anions across the membrane—electrolyte interface as well as the principle of electroneutrality. The results showed the importance of membrane swelling there is a loss of superselectivity, in that there is a decrease in the counterion/co-ion mobility, with greater swelling. 

Although the problem of the liquid membrane potential was solved in principle by Nemst, a discussion developed in the ensuing two decades between Bauer [6], who developed the adsorption theory of membrane potentials, and Beutner [10,11,12], who based his theories on Nernst s work. This problem was finaly solved by Bonhoeffer, Kahlweit and Strehlow [13], and by Karpfen and Randles [49]. The latter authors also introduced the concept of the distribution potential. 

Electrochemistry finds wide application. In addition to industrial electrolytic processes, electroplating, and the manufacture and use of batteries already mentioned, the principles of electrochemistry are used in chemical analysis, e.g.. polarography, and electrometric or conductometric titrations in chemical synthesis, e.g., dyestuffs, fertilizers, plastics, insecticides in biolugy and medicine, e g., electrophoretic separation of proteins, membrane potentials in metallurgy, e.g.. corrosion prevention, eleclrorefining and in electricity, e.g., electrolytic rectifiers, electrolytic capacitors. 

A schematic representation of a FRET-based voltage sensor assay is shown in Fig. 13. The assay principle was first published [105] and then further improved [106] by Gonzalez and Tsien, then commercialized [107], and is now available from Panvera [108]. The FRET donor is a coumarin dye, which is covalently linked to a phosphoHpid. The acceptor is a highly fluorescent, membrane-soluble anionic ox-onol dye. When the cell membrane is loaded with the dyes, the phospholipid anchors the coumarin donor to the outside of the cell, whereas the oxonol dye is accumulated in the ceU membrane. The distribution of the anionic oxonol in the membrane depends on the polarity of the membrane potential if the oxonol dye is located on the extracellular side of the membrane in close proximity to the coumarin donor, FRET occurs and the emission is mostly at 580 nm. If the polarity changes, the oxonol rapidly translocates to the intracellular side of the membrane, too far from the coumarin donor for FRET, and the emission is mostly at 460 nm. 

The principle of the reconstruction is that, under space-clamp conditions, the observed changes in membrane potential represent charging and discharging of the membrane capacitance by the sum of all transmembrane currents according to the following equation ... 

Le Chatelier s principle, 82 London dispersion force, 69 membrane potential, 76 micelle, 74... 

Although the large scale industrial utilisation of ion-exchange membranes began only 20 years ago, their principle has been known for about 100 years [1]. Beginning with the work of Ostwald in 1890, who discovered the existence of a "membrane potential" at the boundary between a semipermeable membrane and the solution as a consequence of the difference in concentration. In 1911 Donnan [2] developed a mathematical equation describing the concentration equilibrium. The first use of electrodialysis in mass separation dates back to 1903, when Morse and Pierce [3] introduced electrodes into two solutions separated by a dialysis membrane and found that electrolytes could be removed more rapidly from a feed solution with the application of an electrical potential. 

Pumping mechanism, cytochrome c oxidase basic physical principle, 79—80 Coulomb machine gun, 80 le/lH-t pumping ratio, 78 membrane potential, 83—84 pK quantum mechanics/molecular mechanics calculations, 84 proton collecting antenna and proton conducting channels, 83 proton loading site (PLS), 80, 82—83 pump element, heme a, 78 water chains, 82... 

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