Workshop on Ion Channels, Mon, 08 Oct, 2007
Speaker: Zuzanna Siwy
Abstract
Biological ion channels are protein nanopores in fragile lipid membranes. Ion channels open and close ('gate') and selectively transport some types of ions. We have made conical nanopores in strong polymer foils that have transport properties similar to transport properties of biological channels. No lipid bilayer is involved, so the system is simple and robust although leak resistance is larger than 100 gigohm. The single nanopores are tapered cones with openings of diameter ~ 600 nm and ~ 5 nm. The single nanopores were prepared by the track-etching technique of irradiating a polymer film with single swift heavy ions, followed by chemical etching of the latent tracks left by ions. The walls of the pores have carboxylate groups with surface density ~1 per nm2.
Transport properties of these nanopores were studied in a variety of solutions in the voltage range between –1.0V and +1.0V. In KCl solutions these single asymmetric nanopores are cation selective and rectify with a ratio of limiting conductances ~ 4 - 10. The K+ ions flow more easily, with lower resistance, from the smaller to larger opening.
Voltage dependent block occurs in synthetic conical nanopores more or less as it does in biological inward rectifiers. Additionally, calcium induced anomalous mole fraction effect was observed in nanopores with diameter < 6 nm. At certain conditions, calcium, cobalt, and manganese ions in sub-millimolar concentrations induce two-state, voltage-dependent fluctuations of ion current with opening and closing times specific for a given divalent cation. The frequency of switching between open and closed state can be regulated between hundreds of Hz and fraction of Hz by the type and concentration of the divalent cations.
URL: www.ricam.oeaw.ac.at/specsem/ssqbm/participants/abstracts/index.php
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