Membranes potential across

One additional benefit is that by continuously pumping more Na ions out than K+ ions into the cell, it results in a higher intracellular K+ ion concentration than might be expected. Since the K+ ion channel is open, the K+ ions diffuse out to an extect dependent upon the concentration difference, so that the Na+/K+ ATPase contributes to the magnitude of the membrane potential across a cell. 

It should be noted that the electrochemical gradient across the mitochondrial membrane is not novel or unusual membrane potential across the plasma membrane of many cells is set up, due to the movement of K+ ions across the membrane. This is particularly important in muscle or nerve (Figure 9.8). 

Figure 9.8 Simple diagram of mitochondrial H -ion movement and axonal K -ion movement to establish membrane potentials across membranes. Note that H movement from the mitochondrial matrix to the outer surface of the inner membrane requires a specific proton pump that requires energy, which is transferred from electron transfer, whereas the K ion movement occurs via an ion channel with energy provided from the concentration difference of K ions on either side of the membrane (approximately 100-fold). The movement of both the protons and K ions generates a membrane potential. The potential across the membrane of the nerve axon provides the basis for nervous activity (see Chapter 14).

A proton ionophore "short-circuits" the proton current, so that both the proton gradient and membrane potential across the inner mitochondrial membrane are collapsed. No phosphorylation of ADP can take place, but electron... 

As a specific example, we will use the Goldman equation to evaluate the membrane potential across the plasma membrane of Nitella translucens. The concentrations of K+, Na+, and Cl- in the external bathing solution and in its... 

The transfer of the information described in the preceding sections of this chapter to the in vivo situation is a matter where opinions are sharply divided, even if more than 20 years have elapsed since the discovery by Vasington and Murphy [4]. One key problem, naturally, is the impossibility of reproducing the composition and the conditions of the cytosol in in vitro experiments. The above mentioned effect of Mg on the rate of Ca influx into mitochondria is but one striking example of the difficulties inherent to the extrapolation to the in situ conditions. Of interest in this respect are recent experiments [124,125] in which methods have been devised to estimate simultaneously the membrane potential across the plasma membrane and the mitochondria of nerve endings in situ. The conclusion of this work has been that the concentration of free Ca in the cytosol correlates directly to the membrane potential across the mitochondrial membrane, and is maintained at a steady-state level below 1 jaM. Simulation of the in situ conditions has also been the aim of studies [126] in which isolated liver endoplasmic reticulum has been added to media in which isolated liver mitochondria were made to take up Ca, or in which liver cells have been treated with digitonin to abolish the permeability barrier of the plasma membrane. It was found that respiring mitochondria lower the external Ca " concentration to about 0.5 /iM. The addition of endoplasmic reticulum vesicles produces a further decrease of the external Ca " to about 0.2 jaM. Thus, mitochondria... 

Fig. 24. Time responses of membrane potential across poly(vinyl chloride) membrane containing spirobenzopyran with a long alkyl chain upon UV and visible light irradiation [54], NaCl concentration in solution c, and C2 l M. a) UV irradiation from the side of Cj b) visible irradiation from the side of C2 c) UV irradiation from the side of Cj d) visible irradiation from the side of c ...

Electrode to measure membrane potential across the plasma membrane of the presynaptic cell... 

Matsumoto. H. et al.. Membrane potential across reverse osmosis membranes under pressure gradient, J. Colloid Inteif. Sci., 309, 272, 2007. 

Huda, R. Kiyono, Tasaka, T. Yamaguchi and T. Sata, Thermal membrane potential across anion-exchange membranes with different benzyltrialkylammonium groups, Sep. Purify. Techrtol., 1998, 14, 95-106. 

R. Kiyono, Y. Tanaka, O. Sekiguchi and M. Tasaka, Thermal membrane potential across cation-exchange membranes for various halide solutions, Colloid Polym. Sci., 1993, 271, 1183-1190. 

T. Hanaoka, R. Tanaka, M. Tasaka, M. Hamada and K. Yoshie, Thermal membrane potential across test anion-exchange membrane Aciplex STA and the transported entropy of counterions, Maku (Membr.), 1993,18, 363-370. 

Figure 2.4.3 Model for treating the membrane potential across a glass barrier.

For example, when tissues were deprived of sodium for several days the site density increased 3-fold from around 250//im, but more importantly there was a proportional increase in the level of transport which was maintained by the epithelium [197] (Figure 1.15). This effect seems an important homeostatic device possessed by the cell to deal with exposures to divergent sodium concentrations. Furthermore, the result indicates that the entry step, rather than the exit step from the epithelium which requires sodium pumping, is the rate determinant of the level of transport. The time course of the effect of sodium deprivation may mean that it is dependent on the de novo synthesis of new membrane permeases. However, increasing the membrane potential across the mucosal face of the cells causes an immediate appearance of new channels, while reducing the potential does the converse [198], indicating that there are binding sites (and... 

Figure 11.1. Experimental setup for monitoring oscillations in trans-membrane potential across the membrane.

Membranes may have various physical and chemical structures and hence are able to restrict transport processes by having different permeabilities for different substrates. Determining properties of equilibrium across and within a membrane may help in understanding the transport phenomena through membranes. Besides thermal equilibrium, the principle of electroneutrality is also satisfied. Because of the absence of mechanical equilibrium, a pressure difference known as osmotic pressure exists between subsystems separated by the membrane. In the case of substrates in ion form, both nonpermeating and permeating ions create an electrical potential difference known as membrane potential across the membrane. For the separated parts of A and B, electrochemical equilibrium for permeating species k is... 

Potentiometric detection is based on the detection of a membrane potential across the membrane of a probe electrode. Potentiometric probes measure a membrane potential linearly dependent on the logarithm of the activity of a primary ion. Experimentally, a typical setup would be... 

The active site of the oxygen-evolving enzyme is arranged so that the protons formed during water oxidation are released into the thylakoid lumen. These protons contribute to the electrochemical proton potential. The thylakoid membrane contains aprotein that functions to transport Cl across the membrane. Proton accumulation in the thylakoid lumen is electrically balanced in large part by Cl uptake. As a result, thylakoids accumulate HCl and the membrane potential across the membrane is low. The pH inside the lumen during steady-state photosynthesis is about 5.0. 

Upward deflection indicates absorbance decrease at 526nm and is consistent with the foimation of a membrane potential across the vesicles, positive outside. 

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