Ion transport across transmembrane pores

¹ University of Groningen, The Netherlands
² University of Queensland, Brisbane, Australia

^* To whom correspondence should be addressed. E-mail: s.j.marrink{at}rug.nl.

Submitted on November 17, 2006
Revised on January 10, 2007
Accepted on 7 February 2007

	Abstract

To study the pore mediated transport of ionic species across a lipid membrane, a series of molecular dynamics simulations have been performed of a DPPC bilayer containing a pre-formed water pore in the presence of sodium and chloride ions. It is found that the stability of the transient water pores is greatly reduced in the presence of the ions. Specifically, the binding of sodium cations at the lipid/water interface increases the pore line tension resulting in a destabilization of the pore. However, the application of mechanical stress opposes this effect. The flux of ions through these mechanically stabilized pores has been analyzed. Simulations indicate that the transport of the ions through the pores depends strongly on the size of the water channel. In the presence of small pores (radius < 1.5 nm) permeation is slow, with both sodium and chloride permeating at similar rates. In the case that the pores are larger (radius > 1.5 nm) a crossover is observed to a regime where the anion flux is greatly enhanced. Based on these observations a mechanism for the basal membrane permeability of ions is discussed.

Key Words: computer simulations, membrane permeability, membrane rupture, molecular dynamics, water channels

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