Poster Presentation 2014 International Biophysics Congress

Nano-scale ion sequestration using tethered lipid bilayers to determine the polarity selectivity of ion channel conductance (#319)

Charles G. Cranfield 1 , Bruce Cornell 2
  1. University of Technology Sydney, Ultimo, NSW, Australia
  2. SDx Tethered Memebranes Pty Ltd, Roseville, NSW, Australia

The selectivity of a peptide or protein ion channel to ionic polarity may be measured using patch clamp electrophysiology or black lipid membrane (BLM) techniques. However, it requires the exchange of the electrolyte solutions which for a fragile free floating membrane can cause damage to the membrane integrity. We describe here a convenient alternative, using a tethered bilayer lipid membrane (tBLM)1 to demonstrate the cation selectivity of the well-characterised ion conducting peptide gramicidin-A (gA). The nano-scale spacing between a tBLM and its supporting gold electrode can be utilized to determine the polarity selectivity of ion channels embedded in the membrane. The technique relies upon the application of a bias voltage to sequester ions of a chosen polarity into the reservoir region between the gold electrode and the tethered membrane. A comparison of the ion channel conductance, in the presence of either a positive or negative bias, and read using AC swept frequency impedance spectroscopy, demonstrates the polarity dependence of the channel. This techniques is used to demonstrate the cation specificity of the ion channel gramicidin-A. In addition, we use Pulsed Amperometry to measure the intrinsic voltage dependent conduction of gramicidin A, which is independent of the polarity selectivity.

  1. 1. Charles G. Cranfield, Bruce A. Cornell, Stephan L. Grage, P. Duckworth, S. Carne, Anne S. Ulrich and B. Martinac, Biophysical Journal, 2014, 106, 182-189.