The drift approximation solves the Poisson, Nernst-Planck, and continuum equations in the limit of large external voltages |
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Authors: | Alexander Syganow E. von Kitzing |
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Affiliation: | (1) Abteilung Zellphysiologie, Max-Planck-Institut für Medizinische Forschung, Postfach 103820, D-69028 Heidelberg, Germany e-mail: vkitzing@sunny.MPImF-Heidelberg.mpg.de, DE |
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Abstract: | Nearly linear current-voltage curves are frequently found in biological ion channels. Using the drift limit of the substantially non-linear Poisson-Nernst-Planck equations, we explain such behavior of diffusion-controlled charge transport systems. Starting from Gauss' law, drift, and continuity equations we derive a simple analytical current-voltage relation, which accounts for this deviation from linearity. As shown previously, the drift limit of the Nernst-Planck equation applies if the total electric current is dominated by the electric field, and integral contributions from concentration gradients are small. The simple analytical form of the drift current-voltage relations makes it an ideal tool to analyze experiment current-voltage curves. We also solved the complete Poisson-Nernst-Planck equations numerically, and determined current-voltage curves over a wide range of voltages, concentrations, and Debye lengths. The simulation fully supports the analytical estimate that the current-voltage curves of simple charge transport systems are dominated by the drift mechanism. Even those relations containing the most extensive approximations remained qualitatively within the correct order of magnitude. Received: 24 September 1998 / Revised version: 22 January 1999 / Accepted: 22 January 1999 |
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Keywords: | Nernst-Planck equation Gauss' law Poisson equation Continuity equation Drift charge transport mechanism |
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