Membranes electrical properties

The discussion given in this section shows that non-homogeneity of membrane electrical properties is widespread and markedly influences ionic sorption and diffusion behaviour. Proper understanding of these effects is, therefore, important and may be expected to contribute materially to the design of more highly permselective membranes. 

THC and CBD differ in their action on membrane electrical properties. It has also been found that THC causes large shifts in the transition temperature of membrane lipids [ 110, 111 ]. A possible relationship between this effect and microsomal demethylase activity was observed, and it was suggested that THC could influence enzymatic action by membrane effects. 

Harder, D.R., Brann, L., and Halpern, W. (1983) Altered membrane electrical properties of smooth muscle cells from small cerebral arteries of hypertensive rats. Bloodvessels, 20 154-160. 

More recently, dielectrophoretic studies have for instance been reported on T-lymphocytes (Pethig and Talary, 2007) and on how cell destruction during dielectrophoresis can be minimized (or used) by appropriate choice of AC frequency and amplimde (Menachery and Pethig, 2005). Dielectrophoresis has also been used for measurement of membrane electrical properties such as capacitance and conductance for insulin-secreting pancreatic cells (Pethig et al., 2005). 

L.F. Liu, S.C. Yu, L.G. Wu, C.J. Gao, Study on a novel antifouling polyamide-urea reverse osmosis composite membrane (ICIC-MPD)—III. Analysis of membrane electrical properties, J Memb Sci, 310 (2008) 119-128. 

Researchers at the MoneU Center (Philadelphia, Pennsylvania) are using a variety of electrophysical and biochemical techniques to characterize the ionic currents produced in taste and olfactory receptor cells by chemical stimuli. These studies are concerned with the identification and pharmacology of the active ion channels and mode of production. One of the techniques employed by the MoneU researchers is that of "patch clamp." This method aUows for the study of the electrical properties of smaU patches of the ceU membrane. The program at MoneU has determined that odors stimulate intraceUular enzymes to produce cycUc adenosine 3, 5 -monophosphate (cAMP). This production of cAMP promotes opening of the ion channel, aUowing cations to enter and excite the ceU. MoneU s future studies wiU focus on the connection of cAMP, and the production of the electrical response to the brain. The patch clamp technique also may be a method to study the specificity of receptor ceUs to different odors, as weU as the adaptation to prolonged stimulation (3). 

Conductivity. Conductivity is an electrical property of excitable tissue which ensures that if one area of a membrane is excited to full activity, that area excites adjacent areas. Conduction of an impulse varies direcdy with the rate of development of phase 0 and the ampHtude of the action potential. Phase 0 is faster, and ampHtude of the action potential is greater, the more negative the transmembrane potential at the time of initiation of the impulse. Conduction velocity is faster when phase 0 is fast. 

By the time the next overview of electrical properties of polymers was published (Blythe 1979), besides a detailed treatment of dielectric properties it included a chapter on conduction, both ionic and electronic. To take ionic conduction first, ion-exchange membranes as separation tools for electrolytes go back a long way historically, to the beginning of the twentieth century a polymeric membrane semipermeable to ions was first used in 1950 for the desalination of water (Jusa and McRae 1950). This kind of membrane is surveyed in detail by Strathmann (1994). Much more recently, highly developed polymeric membranes began to be used as electrolytes for experimental rechargeable batteries and, with particular success, for fuel cells. This important use is further discussed in Chapter 11. 

Montal, M., and P. Mueller, Formation of bimolecular membranes from lipid monolayers and a study of their electrical properties, Proc. Natl. Acad. Sci. USA, 69, 3561 (1972). 

ENTER Membranes LLC has developed Teklon— a highly porous, ultrahigh molecular weight polyethylene separator for lithium-ion batteries. At the writing of this publication, the separator is available in small quantities. Pekala et al. characterized Celgard, Setela, and Teklon separators in terms of their physical, mechanical, and electrical properties. ... 

At the same time (1902), a membrane theory was proposed for the electrical properties of cells and tissues by Overton [80] and Bernstein [8], whose principles remain valid to the present day. 

The second assxmiption of the model that the characteristic buildup time is chemical-physical controlled, implies that this time is dependent on the chemical, physical and electrical properties of the foulant and the membrane but not on the flow. 

In another type, mammalian cells or plasma membranes are used as electrical capacitors. Electrical impedance (El) uses the inherent electrical properties of cells to measure the parameters related to the tissue environment (Kyle et al., 1999). The mechanical contact between cell-cell and cell-substrates is measured via conductivity or El (Deng et al., 2003 ... 

We have only very modest experience with the influence of radiation on the membrane systems discussed. We know, however, that the sterilization of such membranes for their clinical application in ion-selective electrodes may be achieved by using X-rays. The electric properties seem to remain unchanged. 

The effects of digitalis on the electrical properties of the heart are a mixture of direct and autonomic actions. Direct actions on the membranes of cardiac cells follow a well-defined progression an early, brief prolongation of the action potential, followed by shortening (especially the plateau phase). The decrease in action potential duration is probably the result of increased potassium conductance that is caused by increased intracellular calcium (see Chapter 14). All these effects can be observed at therapeutic concentrations in the absence of overt toxicity (Table 13-2). 

Reverdin EC, Weingart R Electrical properties of the gap junctional membrane studied in rat liver cell... 

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