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Synthetic Nanopores as a Test Case for Ion Channel Theories: The Anomalous Mole Fraction Effect without Single Filing

Dirk Gillespie ^*, Dezs Boda ^* , Yan He , Pavel Apel  and Zuzanna S. Siwy 

^* Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois; Department of Physical Chemistry, University of Pannonia, Veszprém, Hungary; Department of Physics and Astronomy, University of California, Irvine, California; and Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, Moscow Region, Russia

Correspondence: Address reprint requests to Dirk Gillespie, E-mail: dirk_gillespie{at}rush.edu.

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.

This article has been cited by other articles:

				D. Gillespie and D. Boda The Anomalous Mole Fraction Effect in Calcium Channels: A Measure of Preferential Selectivity Biophys. J., September 15, 2008; 95(6): 2658 - 2672. [Abstract] [Full Text] [PDF]