Membrane potential difference

Assuming that 3 H are transported per ATP synthesized in the mitochondrial matrix, the membrane potential difference is 0.18 V (negative inside), and the pH difference is 1 unit (acid outside, basic inside), calculate the largest ratio of [ATP]/[ADP] [P,] under which synthesis of ATP can occur. 

A. Oscillation of the Membrane Potential Difference Under an Appiied Current [22,23]... 

Van der Schoot C, van Bel AJC. Mapping membrane potential differences and dye coupling in intemodal tissues of tomato. Planta 1990 182 9-21. 

The scheme of reactions (5)-(8) is similar in certain aspects to that of electron transfer processes occurring in the membranes of photosynthesiz-ing organisms, where the light absorption also induces a trans-membrane potential difference. The above scheme of processes in multilayer systems explaining the appearance of the photoelectromotive force requires further refinement. But even the data available at present allow these systems to be regarded firstly as convenient models for analyzing the processes occurring... 

The results in Figure 3, obtained with membrane vesicles, show that imposition of a membrane potential difference (inside negative) greatly enhanced the peak uptake of a solute taken up by a Na+-dependent route. The potential difference could be increased by using lipid soluble anions or valinomycin in vesicles with Kf KJ (Colombini and Johnstone, 1974 Murer and Hopfer, 1974 Sigrist-Nelson et al., 1975 Lever, 1977 Hammerman and Sacktor, 1978 Hopfer, 1978 Wright et al 1983 Kimmich etal., 1991). 

When the mobile ion in the solid membrane is an anion, the basic equations giving the membrane potential differ with respect to the sign of the contributing terms. The equilibrium giving rise to the Donnan potential is now... 

When the lymphocytes are placed in 0.6 isosmotic medium, the cells swell and this deformation in cell structure triggers a large increase in the permeability of the membrane to chloride. It becomes the most permeant ion. As a result, the Goldman equation predicts that the membrane potential difference should depolarize, because the ratio of cell chloride concentration to medium concentration will generate a much lower potential difference. When the potential difference becomes less negative inside the cell, the restraining force on potassium exit from the cells is reduced and potassium is able to leave the cell. However, it cannot go far without an accompanying anion, and that anion is the chloride anion. The net result is the exit of potassium chloride. 

The effect of the membrane potential difference,(E"-E ), on the rate of methanol formation is shown in Figure 2. 

The disturbance in the membrane potential difference is corrected by hemodialysis or protein restriction, suggesting a causative role for dialyzable products of protein metabolism. Phenolic acids (W2), methylguanidine, atriopeptins, and tissue hypothyroidism have been suggested as causes for the decreased sodium potassium ATPase activity (C23). 

To pump one Ca + ion out of a cell against a concentration gradient of about 10 (1 /aM 1 mM) requires that at least 3 Na ions pass in the opposite direction, thus maintaining AAG < 0. What then will be the effect of a membrane potential difference Most animal cells, particularly excitable cells such as nerve and muscle cells, have resting potential differences, A P, over the plasma membrane of 30 to 90 mV (cytoplasm negative). For this value we find the change in free energy, AAG, for the transport of one mol Ca to be... 

With A F = 150 mV, this ratio is calculated to be 8.4 x 10 at 25°C. It is evident that, as long as the Ca " influx would not lower the membrane potential difference, the Ca " uniporter has a very high pumping potential. Measured values of the pumping rate, Vmax are indeed high (>10 nmol/mg proteinand probably limited only by tbe rate of electron transport and H extrusion in the mitochondria. 

Both Na and K are involved in various electrophysio-logical functions in higher animals. The [Na ] [K ] ratio is different in intra- and extra-cellular fluids, and the concentration gradients of these ions across cell membranes are the origin of the trans-membrane potential difference that, in nerve and muscle cells, is responsible for the transmission of nerve impulses. A balanced diet therefore includes both Na and salts. Potassium is also an essential plant nutrient, and salts are widely used as fertilizers. Uses of Li and Na in batteries are highlighted in Box 10.3, and the use of KO2 in breathing masks is described in Section 10.6. 

A.S. Michaels and R.G. Miekka, Polycation-polyanion complexes Preparation and properties of poly(vinylbenzyltrimethylammonium) and poly(styrenesulfonate), J. Phys. Chem., 1961, 65, 1765-1773 A.S. Michaels, L. Mir and N.S. Schneider, A conductometric study of polyaction-polyanion reactions in dilute solution, J. Phys. Chem., 1965, 69, 1447-1455 S.J. Reid, J. Th. Overbeek, W. Vieth and S.M. Fleming, Membrane potential differences with the polyelectrolyte complex - poly(vinyltrimethy-lammonium)-poly(styrenesulfonate), J. Colloid Polym. Sci., 1968, 26, 222-229, O. Yano and Y. Wada, Effect of sorbed water on dielectric and mechanical properties nf nnlvinn enmnlex../ Ann Polvm. Sci.. 1980. 25. 1723-1735. 

Cunningham, J.N., Carter, N.W., Rector, F.C., and Seldin, D.W. (1971) Resting Membrane Potential Difference of Skeletal Muscle in Normal Subjects and Severely 111 Patients, J. Clin. Investig. 50,49-59. 

The observed membrane potential differences, of up to 100 mV may correspond to average values of the electric field strength, of about 100kVcm when the thickness, rf, of the dielectric membrane part is about 10 nm. 

Membrane potential Difference in voltage or electrical potential across a membrane. 

Induction step - the field induced membrane potential difference increase reached a critical value at the polar position facing the electrodes, and this gave local defects (may be due to kinks in the lipid chains). A mechanical stress was present with a magnitude that depends on the buffer composition. These defects could be associated with water wires. Due to the potential charging time, the structural transition of the membrane affected a defined cap size on the cell surface. 

The source of the membrane stmctural modification is a modulation of the membrane potential difference. This is due to the dielectric character of the membrane. From a soft matter point of view, a cell can be described as an insulating shell containing a conducting solution (the cytoplasm with a conductivity Xi) and in suspension in a conducting buffer (the external solution with a conductivity Xo). A cell in a field behaves as a charging spherical capacitor. The induced potential difference A Pg can be written as (when steady states are reached) ... 

This membrane potential difference alteration was reached after a very short charging time (in the microsecond time range) ... 

Electropulsation and its results on a cell are under the control of cellular parameters and experimental settings (field strength, pulse duration). It is a noninvasive way to alter in a selective manner the membrane potential difference on the microsecond time range. 

The external field induces a position-dependent modulation of the membrane potential difference linearly related to the intensity of the applied field. Theoretical predictions from Eq. 1 are valid only under the hypothesis that ... 

The metal potential difference across the cell may be obtained by summing the potential drop from the overpotentials, the membrane potential difference, and the Nernst potentials. 

At pH 7.0, it is -131 mV (a value also found by studies of distribution of a lipophilic cation). The proton motive force across the inner membrane of this gastric denizen is therefore -221 mV, the sum of the pH gradient and the membrane-potential difference. 

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