Membrane potentials complications

If there is a net transport of charge across the membrane, the membrane potential will influence the solute transfer and also be affected by it, complicating the data treatment. The starting point for most descriptions of the internalisation flux of permeant ions, i, is the one-dimensional Nernst-Planck equation (cf. equation (10)) that combines a concentration gradient with the corresponding electric potential gradient [270] ... 

This chapter is concerned with processes that lead to formation of ISE membrane potentials. The membrane potentials of electrodes with liquid membranes containing a dissolved ion-exchanger ion or a dissolved ionophore (ion carrier), and of electrodes with solid or glassy membranes will be considered. More complicated systems, for example ISEs with a gas gap and enzyme electrodes, will be discussed in chapters 4 and 9. 

Catterall That story has become even more complicated in more recent experiments. We have found that both membrane potential and PKC influence the functional effects caused by phosphorylating individual PKA sites. 

Daptomycin is a lipopeptide that binds to bacterial membranes and canses a rapid depolarization of membrane potential, which inhibits protein, DNA, and RNA synthesis, resulting in bacterial cell death. Daptomycin is indicated in treatment of complicated skin and skin structure infections caused by susceptible strains of Gram-positive microorganisms. 

This idea is the essence of ion-selective electrodes. Measurements with these devices are essentially determinations of membrane potentials, which themselves comprise junction potentials between electrolyte phases. The performance of any single system is determined largely by the degree to which the species of interest can be made to dominate charge transport in part of the membrane. We will see below that real devices are fairly complicated, and that selectivity in charge transport throughout the membrane is both rarely achieved and actually unnecessary. 

It is not possible here to investigate more complicated examples of the Donnan effect. Suffice it to say that membrane potentials (which can be produced by mechanisms other than the Donnan effect) play an important role in many colloid phenomena, especially in biological systems. 

As the mathematical representation of the complete overshoot curve is very complicated, only the amplitude of the peak is usually taken as an indicator of secondary active transport, provided that other causes of an overshoot phenomenon, such as osmotic swelling or temporary changes in membrane potential, can be excluded. 

It is thought that the individual enantiomers internet with different channel states, open and inactivated, the binding sites of which have opposite stereochemical requirements [63], The situation becomes more complicated as the activating properties of the 5-enantiomers of Bay K 8644 and PN 202 791 appear to be dependent on membrane potential, and they become antagonists at depolarizing potentials [64,65]. 

A number of quite different techniques have evolved to make measurements of the various electric potentials associated with membranes but particular measurements must rely on the physical differences between the potentials. In order to avoid interpretative difficulties due to interference between each potential, clearly it is necessary to have a very clear understanding of the physical nature of both the potential as well as the measurement technique. In addition, however, membranes also possess other properties which often complicate assignments of specific values for the membrane potentials. 

The relationship between electrical potential and a pH across the thylakoid membrane is complicated. Electrical potential affected the pump in Cyt, -PQ cycle[8][9][10], and inversely, pH was thought to influence the electrical potential[12]. Such a relation might be necessary for the regulation of conformational change of thylakoids under light. From the results presented above, we... 

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