Conduction in membranes

The gramicidin family of linear polypeptides represents a biologically viable channel system of related peptides in which specific changes in amino acid composition can be correlated with cation binding selectivity and transport. The parent molecule of this family of polypeptides, gramicidin A, has the amino acid sequence shown in Fig. 1. This relatively simple molecule is probably the best characterized ion channel (both structurally and functionally) and has, to date, been the principal proving-ground for many of our ideas about the molecular nature of ion conduction in membranes. ... 

Koch, K., and Kaupp, B. (1985). Cyclic GMP Directly Regulates a Cation Conductance in Membranes of Bovine Rods by a Cooperative Mechanism, J. Biol. Chem. 260 6788-6800. 

It is well known that, in general, BaCeOs oxides have higher protonic conductivity than SrCe03-based oxides. The increase of protonic conductivity in membrane material would be beneficial. A large number of cells with a barium cerate membrane were used in electrocatalytic ammonia synthesis. The results showed that there is no significant improvement between cells with SrCe03-based or BaCeOa.based oxides. It can be concluded that materials with protonic conductivity of 10 —10 S/cm would be adequate for ammonia synthesis. 

Another approach to achieving proton conductivity in membranes at high temperatures is to replace water with another proton transport-assisting... 

Dechecchi, M. C. Cabrini, G. Chloride conductance in membrane vesicles from human placenta using a fluorescent probe implications for cystic fibrosis. Biochim. Biophys. Acta 1988, 945, 113-120. 

Local anesthetics produce anesthesia by blocking nerve impulse conduction in sensory, as well as motor nerve, fibers. Nerve impulses are initiated by membrane depolarization, effected by the opening of a sodium ion channel and an influx of sodium ions. Local anesthetics act by inhibiting the channel s opening they bind to a receptor located in the channel s interior. The degree of blockage on an isolated nerve depends not only on the amount of dmg, but also on the rate of nerve stimulation (153—156). 

PVF resins have also been used in a variety of other appHcations, including conductive films (152), electrophotographic binders (153), as a component for inks (154), and in membranes (155,156), photoimaging (157), solder masks (158), and reprographic toners (159). 

Practical appHcations have been reported for PVP/ceUulosics (108,119,120) and PVP/polysulfones (121,122) in membrane separation technology, eg, in the manufacture of dialysis membranes. Electrically conductive polymers of polyaruline are rendered more soluble and hence easier to process by complexation with PVP (123). Addition of small amounts of PVP to nylon 66 and 610 causes significant morphological changes, resulting in fewer but more regular spherulites (124). 

Cross-flow-elec trofiltratiou (CF-EF) is the multifunctional separation process which combines the electrophoretic migration present in elec trofiltration with the particle diffusion and radial-migration forces present in cross-flow filtration (CFF) (microfiltration includes cross-flow filtration as one mode of operation in Membrane Separation Processes which appears later in this section) in order to reduce further the formation of filter cake. Cross-flow-electrofiltratiou can even eliminate the formation of filter cake entirely. This process should find application in the filtration of suspensions when there are charged particles as well as a relatively low conduc tivity in the continuous phase. Low conductivity in the continuous phase is necessary in order to minimize the amount of elec trical power necessaiy to sustain the elec tric field. Low-ionic-strength aqueous media and nonaqueous suspending media fulfill this requirement. 

Gaskets are veiy important, since thev not only keep the streams separated and prevent leaks from the cell, they have the manifolds to conduct feeds. Doth concentrate and diluate, built into them. No other practical means of feeding the stack is used in the veiy cramped space required by the need to keep cells thin because the diluate has veiy low conductivity. The manifolds are formed by ahgning holes in membrane and gasket. 

Polymeric ionic conductors. One of the most unexpected developments in recent decades in the whole domain of electrochemistry has been the invention of and gradual improvements in ionically conducting polymeric membranes, to the... 

Class II drugs are classical (3-adrenoceptor antagonists such as propranolol, atenolol, metoprolol or the short-acting substance esmolol. These drugs reduce sinus rate, exert negative inotropic effects and slow atrioventricular conduction. Automaticity, membrane responsiveness and effective refractory period of Purkinje fibres are also reduced. The typical extracardiac side effects are due to (3-adrenoceptor blockade in other organs and include bronchospasm, hypoglycemia, increase in peripheral vascular resistance, depressions, nausea and impotence. 

Within the nervous system, ChEs were shown to be involved in membrane conductance and transmission of excitatory amino acids, learning and memory, neurite growth, neuritic translocation and acute stress reactions. Recent findings propose AChE s involvement in apoptosome formation [2]. 

Inward Rectification refers to decreased conductance upon membrane depolarization. In classical inward rectifier K+ channels, rectification is strong and currents rapidly decline at membrane potentials positive to the reversal potential, in contrast to other Kir channels in which rectification is weak and currents decline only gradually at potentials positive to the reversal potential. 

Low conductivity in the membrane High conductivity (Small lb) (Urge Id)... 

Another method to synthesize hollow nanocapsules involves the use of nanoparticle templates as the core, growing a shell around them, then subsequently removing the core by dissolution [30-32]. Although this approach is reminiscent of the sacrificial core method, the nanoparticles are first trapped and aligned in membrane pores by vacuum filtration rather than coated while in aqueous solution. The nanoparticles are employed as templates for polymer nucleation and growth Polymerization of a conducting polymer around the nanoparticles results in polymer-coated particles and, following dissolution of the core particles, hollow polymer nanocapsules are obtained. 

Figure 11.5 Chloride distribution and the GABAa response. The change in membrane voltage (Fm) that results from an increase in chloride conductance following activation of GABAa receptors is determined by the resting membrane potential and the chloride equilibrium potential (Fci)- (a) Immature neurons accumulate CF via NKCC, while mature neurons possess a Cl -extruding transporter (KCC2). (b) In immature neurons GABAa receptor activation leads to CF exit and membrane depolarisation while in mature neurons the principal response is CF entry and h5q)erpolarisation. This is the classic inhibitory postsynaptic potential (IPSP)...

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR), a chloride (CF) channel characterised by chloride permeability and secretion, and also by the regulation of other epithelial ion channels (Eidelman et al, 2001). Mutations in the CFTR gene lead to an impaired or absent Cl conductance in the epithelial apical membrane, which leads to defective Cl secretion and absorption across the epithelium. Genistein (Illek et al, 1995 Weinreich et al, 1997) and other flavonoids (Illek and Fisher, 1998) have been shown, in different animal and tissue models, to activate wild-type CFTR and CFTR mutants by (Eidelman et al, 2001 Roomans, 2001 Suaud et al, 2002) ... 

Other blockers of epithelial Cl -channels are of the aryl-amino-benzoate type or phenoxy-acetic-acid type [70]. Very few systematic surveys comparing different classes of blockers in one type of Cl -channel are available at this stage. One such study has been performed in membrane vesicles from kidney cortex [80]. In this study IAA-94 and NPPB (cf. Fig. 2) turned out to be the most potent blocker of conductive Cl -flux. In another systematic survey the Cl -conductance of the sweat duct was examined, and it was found that dichloro-DPC (Fig. 2) was the most potent inhibitor of the transepithelial Cl -conductance [90]. 

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