Membrane surface potentials

R. Pal, W. A. Petri, Jr., Y. Barenholz, and R. R. Wagner, Lipid and protein contributions to the membrane surface potential of vesicular stomatitits virus probed by a fluorescent pH indicator, 4-heptadecyl-7-hydroxycoumarin, Biochim. Biophys. Acta 729, 185-192 (1983). 

Van der Kloot, W. G. Cohen, I. Membrane surface potential changes may alter drug interactions an example, acetyl choline and curare. Science 1979, 203, 1351-1352. 

In this case, the sign of the membrane surface potential (= eij/JkT) coincides with that of the Donnan potential Ydon and becomes zero when becomes zero. Namely, the concentration at which jo changes its sign is given by setting Ydon equal to zero in Eq. (4.120), namely. 

The membrane surface potential roles in modulating ion channels and cell-cell interactions... 

Similar approaches utilising such indicators as FPE to visualise the membrane surface potential ( )s are also routinely employed in our laboratories (17). By correlating the change of the fluorescence and hence surface potential with the addition of net electric charges from the macromolecule that becomes bound, it is possible to quantitate on the basis of the poisson-boltzmann equation above, the number of molecules that become bound. This allows us for example to determine localised molecular interactions on the membrane surface (17, 34). 

Membrane-active compounds can elicit adverse effects in three primary ways. First, compounds that are positively charged at physiologic pH may alter membrane surface potential in a manner proportional to their concentration in the membrane. This in turn could have an adverse effect on membrane function. Second, the chemical may absorb... 

Jucker and Clark (1994) have demonstrated a preferential adsorption of hydrophobic compounds on hydrophobic UF membranes. However, Childress and Elimelech (1996) showed that humic substances adsorb on hydrophilic membranes very rapidly and that the membrane surface potential becomes more negative due to the humic substances. Calcium facilitates the adsorption of negatively charged organics onto negative surfaces. 

Figure 7.6 TFC-S membrane surface potential as a function of solution composition.

Ahn, S.J., Sivaguru, M., Osawa, H., Chung, G.C., Matsumoto, H., 2001. Aluminum inhibits the H -ATPase activity by permanently altering the plasma membrane surface potentials in squash roots. Plant Physiol.126, 1381-1390. 

Surface potentials at the electrode-solution interface have been described by a number of formalisms. The most successful of these originates from Gouy and Chapman whom suggested that Poisson-Boltzmann approaches best describes the state of affairs at the electrode surface in contact with an aqueous solution (further elaborations are outlined by Bockris Reddy). Within Electrochemistry this proved very successful and analogous formalisms were subsequently applied to physical descriptions of biological surfaces. The resultant Poisson-Boltzmann equation with defined boundary conditions can be solved analytically to yield an expression for the membrane surface potential as follows ... 

These expressions however are essentially, mean-field approaches as little account was taken of the molecular diversity that exists in living cell membranes. This is in part due to the evident complexity of such membranes but some modelling simulations have now begun to incorporate such diversity (eg. lipid-protein interactions are emphasised within the context of computational modelling). These are important tasks as there is clearly much local variation in the magnitude of the membrane surface potentials. We have engaged this problem for some years and are able to visualise the spatial variation of the potential about the membrane and cell surface with high molecular and spatial resolution (see below). 

Kinraide, T.B. 2006. Plasma membrane surface potential (psiPM) as a determinant of ion bio-avaUabUity A critical analysis of new and published toxicological studies and a simpb-fied method for the computation of plant psiPM. Environ. Toxicol. Chem. 25 3188-3198. 

Wang, R, D. Zhou, T.B. Kinraide, et al. 2008. Cell membrane surface potential (psiO) plays a dominantrole in the phytotoxicity of copper and arsenate. Plant Physiol. 148 2134—2143. Wang, P., D.M. Zhou, L.Z. Li, et al. 2010. Evaluating the biotic ligand model for toxicity and the alleviation of toxicity in terms of cell membrane surface potential. Environ. Toxicol. Chem. 29 1503-1511. 

Moreover, if the surface potential or surface charge of the colloid has been determined and the solution is of defined ionic content, it is possible to calculate the potential or charge of the surface under investigation by matching the experimentally obtained curves to theoretical calculations based on electrical double layer theory. In the example shown, the best-fit membrane surface charge was —0.00114 Cm and the best-fit membrane surface potential was —64 mV. Furthermore, an important advantage of the colloid probe technique is that it allows exploration of variations in surface electrical interactions at different points on the membrane surface, as the following section shows. 

In addition, many other techniques have been used to determine specific properties ESR spectroscopy, fluorescence measurements using fluorescent markers, black film mea.sure-ments to determine permeabilities, IR spectroscopy to study tail dihedral gauche-dcfccts, measurements of membrane surface potentials, partitioning of small molecules, force measurements between membranes, differential scanning calorimetry to find phase transitions, and doubtlessly countless others. 

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