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Biophys. J. BioFAST: First Published April 7, 2006. doi:10.1529/biophysj.106.084343
© 2006 by the Biophysical Society.

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MEMBRANES

A new model of weak acid permeation through membranes revisited: Does Overton still rule?

Sapar M Saparov 1, Yuri N Antonenko 2 and Peter Pohl 1*

1 Johannes Kepler Universitaet Linz
2 Moscow State University

* To whom correspondence should be addressed. E-mail: peter.pohl{at}jku.at.

Submitted on March 1, 2006
Revised on March 20, 2006
Accepted on 3 April 2006


  Abstract
  According to a recent publication by Thomae, Wunderli-Allenspach and Krämer (Biophys. J. 89 (2005): 1802-1811), membrane bilayers are well permeable to the charged species of aromatic carboxylic acids. At physiological pH, the anions were claimed to be the major diffusing species. In contrast, calculation of the Born energy barrier predicts a 105-fold fold higher permeability for the uncharged (protonated) form. To test the new model, we now have measured both the current carried by the salicylate anion through solvent free planar membranes and the amount of protons transported by the neutral species. The corresponding membrane permeabilities of the charged and protonated forms were 4x10-7cm/s and 1.2 cm/s. These data are in perfect agreement with literature data gathered in the last three decades (compare e.g. Gutknecht and Tosteson, Science, 182 (1973) 1258-61). They indicate that the report by Thomae at al. represents an experimental artefact. The well-documented role of neutral species in the permeation process of weak acids and bases across artificial and natural membranes is out of question. Overton still rules.

Key Words: electrochemical microscopy, microelectrode, planar bilayer, proton transport, unstirred layer




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Copyright © 2006 by the Biophysical Society.