Cellular electrical potential

In a paper on the electrical potential across a copper-ferrocyanide gel membrane, Wilhelm Ostwald suggested that a similar potential represents the electrical potentials of living tissues. Julius Bernstein, a student of Helmholtz, took this suggestion and developed it into the membrane theory of cellular electrical potentials. In this theory, he assumed that the cell membrane is permeable to K but not to anions and Na" ". He also postulated that during an action potential there is a transient local increase of membrane permeability. ... 

If the bulk of cell is adsorbed, the membrane theory of cellular electrical potential is no longer tenable. The same finding is in full harmony with the theory of cellular potentials according to the AI hypothesis, to be discussed below. 

In reviewing the history of the search for the origin of the cellular electrical potential, I discovered the following each of the three models originally chosen for study as models of the cell membranes (oil layer, glass membrane, collodion membrane) eventually was discovered to generate the potential not by virtue of their ionic permeabilities. Rather, they are all surface adsorption potentials. 

G. N. Ling, Two Opposing Theories of the Cellular Electrical Potential A Quarter of a Century of Experimental Testing, Bioelectrochem. Bioenerg. 5, 411 (1978). 

Allelopathic inhibition of mineral uptake results from alteration of cellular membrane functions in plant roots. Evidence that allelochemicals alter mineral absorption comes from studies showing changes in mineral concentration in plants that were grown in association with other plants, with debris from other plants, with leachates from other plants, or with specific allelochemicals. More conclusive experiments have shown that specific allelochemicals (phenolic acids and flavonoids) inhibit mineral absorption by excised plant roots. The physiological mechanism of action of these allelochemicals involves the disruption of normal membrane functions in plant cells. These allelochemicals can depolarize the electrical potential difference across membranes, a primary driving force for active absorption of mineral ions. Allelochemicals can also decrease the ATP content of cells by inhibiting electron transport and oxidative phosphorylation, which are two functions of mitochondrial membranes. In addition, allelochemicals can alter the permeability of membranes to mineral ions. Thus, lipophilic allelochemicals can alter mineral absorption by several mechanisms as the chemicals partition into or move through cellular membranes. Which mechanism predominates may depend upon the particular allelochemical, its concentration, and environmental conditions (especially pH). 

Two hypotheses have been proposed to explain how phenolic acids directly increase membrane permeability. The first is that the compounds solubilize into cellular membranes, and thus cause a "loosening" of the membrane structure so that minerals can leak across the membrane (28-30, 42). Support for this hypothesis comes from the fact that the extent of inhibition of electrical potentials correlates with the log P (partition coefficient of a compound between octanol and water) for various benzoic and cinnamic acid derivatives (Figure 5). 

The aforementioned electrical potentials and the electrochemical events involved in the extra-cellular fluid dynamics caused by them around the tumor (viz. coronas) led Nordenstrom to propose the use of externally applied potential differences to cause changes that might lead to the destruction of the tumor, i.e., ECT of cancerous tissues. In 1978, he reported on the treatment of lung metastases in 20 patients by the method of ECT,10 based on earlier preliminary work on five patients. Since then, he has published very extensive studies on the electrochemical treatment (ECT) of tumors.12"18... 

Ion transport is also often coupled with cellular energy production and with nutrient and product membrane transport. Aside from Papoutsakis work on the influence of methanol transport on growth of methanol-consuming bacteria, the importance of membrane control of nutrient and product fluxes into the cell has been largely ignored by biochemical engineers [25]. Better methods for measuring the pH and electrical potential differences across cell membranes are needed, as is more careful consideration of membrane-mediated processes in cell kinetics models. 

The 1952 Hodgkin-Huxley model for membrane electrical potential is perhaps the oldest and the best known cellular kinetic model that exhibits temporal oscillations. The phenomenon of the nerve action potential, also known as excitability, has grown into a large interdisciplinary area between biophysics and neurophysiology, with quite sophisticated mathematical modeling. See [103] for a recent treatise. 

Potassium channels can have a frequency of one or more channels per square micrometer of membrane surface area. Cellular control can be exerted on the opening of such K+ channels, because concentrations of cytosolic Ca2+ above 3 x 10-4 mol m-3 (0.3 p,M) can inhibit channel opening. Other ion channels in plant membranes are specific for Ca2+ or Cl-. Besides being sensitive to the electrical potential difference across a membrane, some channels apparently open upon stretching of a membrane. Also, many plant cells are excitable and can transmit action potentials, a process in which ion channels are undoubtedly involved. For example, action potentials have been measured for plants responsive to tactile stimuli, such as rapid leaf movements in Mimosa pudica and insectivorous plants (Dionaea spp., Drosera spp.), as well as along the phloem for many species. In addition, ion channels are involved in the long-term maintenance of specific ion concentrations in plant cells. 

Iontophoresis is a method of transferring substances to and from the body for therapeutic or diagnostic purposes by applying an electric potential to enhance their movement across biological membranes. The most common applications of iontophoresis involve the delivery of therapeutic substances across the skin, though there are numerous examples of the use of iontophoresis to treat conditions of the eye, ear, nose, and mouth. Iontophoresis can also be used to remove substances (e.g., glucose) from the body. A technique known as microiontophoresis employs a small capillary probe to study cellular function by releasing precise quantities of active substances. 

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