Electrical potential gradient

Nonporous Dense Membranes. Nonporous, dense membranes consist of a dense film through which permeants are transported by diffusion under the driving force of a pressure, concentration, or electrical potential gradient. The separation of various components of a solution is related directiy to their relative transport rate within the membrane, which is determined by their diffusivity and solubiUty ia the membrane material. An important property of nonporous, dense membranes is that even permeants of similar size may be separated when their concentration ia the membrane material (ie, their solubiUty) differs significantly. Most gas separation, pervaporation, and reverse osmosis membranes use dense membranes to perform the separation. However, these membranes usually have an asymmetric stmcture to improve the flux. 

Kelvin effect The electrical potential gradient caused by a temperature gradient along a conducting wire. Also known as the Thomson Effect. 

This equation shows that the contribution of the two components of the PMF differ with different conditions. In state 4, the electrical potential gradient across the inner membrane can be as high as 300,000 Vcm" and the A pH difference one unit. ATP synthesis only occurs when the PMF is sufficiently large. The phosphorylation potential (AG atp) is lower for ATP synthesis in the matnx (AG atp in = 3AP) for ATP exported to the cytosol (AG ajp out = 4AP) because an extra proton is consumed in importing ADP into the matnx (see text). 

A combination of continuum transport theory and the Poisson distribution of solution charges has been popular in interpreting transport of ions or conductivity of electrolytes. Assuming zero gradient in pressure and concentration of other species, the flux of an ion depends on the concentration gradient, the electrical potential gradient, and a convection... 

The electric potential gradient is thus given by the sum of two expressions ... 

As demonstrated in the preceding section, an electric potential gradient is formed in electrolyte solutions as a result of diffusion alone. Let us assume that no electric current passes through the solution and convection is absent. The Nernst-Planck equation (2.5.24) then has the form ... 

Mass transfer may be influenced by gradients in variables other than concentration and pressure. In the pharmaceutical sciences, gradients in electrical potential and in temperature are two important examples of these other driving forces. Section IV.B.l describes the effect of electrical potential gradients on the transport of ions, and Section IV.B.2 discusses mass transport in the presence of temperature gradients, known as combined heat and mass transfer. 

Em - Pc defines the electrical potential gradient across the mucosal membrane where potential inside the enterocyte is negative. 

The analysis of oxidation processes to which diffusion control and interfacial equilibrium applied has been analysed by Wagner (1933) who used the Einstein mobility equation as a starting point. To describe the oxidation for example of nickel to the monoxide NiO, consideration must be given to the respective fluxes of cations, anions and positive holes. These fluxes must be balanced to preserve local electroneutrality throughout the growing oxide. The flux equation for each species includes a term due to a chemical potential gradient plus a term due to the electric potential gradient... 

These equations yield expressions for the electric potential gradient... 

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] ... 

The only process occurring in a Hquid junction is the diffusion of various components of the two solutions in contact with it. The various mobilities of the ions present in the Hquid junction lead to the formation of an electric potential gradient, termed the diffusion potential gradient. A potential difference, termed the liquid-junction potential, A0x,. is formed between two solutions whose composition is assumed to be constant outside the Hquid junction. 

In a discussion of permeability it is important to recognize that we deal with operational definitions, since the act of measurement influences the state of the system. In your case, applying an electrical potential gradient and performing electrodialysis alter the distribution of ionophore within the membrane. I wonder whether you have attempted to measure permeability by isotopic tracer techniques In this method the distribution of ionophore would not be influenced. Furthermore, information can be obtained on the question of carriers versus channels or pores. It should not be difficult to determine the extent of possible isotope interaction between tracer species and abundant species in the membrane as discussed by Kedem and Essig [J. Gen. Physiol., 48, 1047 (1965)]. Positive isotope interaction would tend to suggest the presence of channels or pores, negative isotope interaction the presence of carriers. 

The transport I mentioned is induced by an electric potential gradient across the membrane. 

The flow velocity in the filter v is again related to the pressure and the electric potential gradients via a generalized Darcy s law of the form... 

The sulfonamide diuretics cause problems through excessive excretion of potassium which diffuses into the urine as Na+ is removed in the distal tubule. This cation exchange is prevented by a different type of diuretic, triamterene (198), which was developed by following the observation that xanthopterin (199) affects renal function. The pyrazine amiloride (200) also increases Na+ output and spares K+, and is used in conjunction with chlorothiazide. It has been shown to reduce the electrical potential gradient along which K+ migrates into the lumen of the tubule. 

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