BIOPHYSICAL THEORY AND MODELING |
Synthetic nanopores as a test case for ion channel theories: The anomalous mole fraction effect without single filing
Dirk Gillespie 1*, Dezso Boda 1, Yan He 2, Pavel Apel 3 and Zuzanna S. Siwy 2
1 Rush University Medical Center
2 University of California, Irvine
3 Flerov Laboratory of Nuclear Reactions
* To whom correspondence should be addressed. E-mail: dirk_gillespie{at}rush.edu.
Submitted on December 18, 2007
Revised on February 20, 2008
Accepted on 27 March 2008
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Abstract |
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The predictions of a theory for the anomalous mole fraction effect (AMFE) are tested experimentally with synthetic nanopores in plastic. The negatively-charged synthetic nanopores under consideration are highly cation selective and 50 Å in diameter at their smallest point. These pores exhibit an AMFE in mixtures of Ca2+ and monovalent cations. An AMFE occurs when the conductance through a pore is lower in a mixture of salts than in the pure salts at the same concentration. For ion channels, the textbook interpretation of the AMFE is that multiple ions move through the pore in coordinated, single-file motion. However, because the synthetic nanopores are so wide, their AMFE shows that single filing is not necessary for the AMFE. It is shown that the AMFE in the synthetic nanopores is explained by a theory of preferential ion selectivity. The unique properties of the synthetic nanopores allow us to experimentally confirm several predictions of this theory. These same properties make synthetic nanopores an interesting new platform to test theories of ion channel permeation and selectivity in general.
Key Words:
Nernst-Planck theory, anomalous mole fraction, synthetic nanopores
