Poster Presentation 2014 International Biophysics Congress

The relative ion permeability of artificial “Selemion©” hydrocarbon membranes used to simulate the properties of biological membranes in undergraduate physiology classes (#464)

Andrew J. Moorhouse 1 , Sean J. Humphrey 1 , Peter H. Barry 1
  1. UNSW Australia, Sydney, NSW, Australia

Living cells function via the generation and propagation of electrical and chemical signals across their plasma membrane resulting from a combination of ion concentration gradients and selective membrane permeability. Demonstrating this key aspect of cellular physiology to large undergraduate classes can be challenging. We have utilized artificial hydrocarbon Selemion@ membranes (a kind gift of Asahi Chemical Company, Japan) sealed inside a simple Perspex bath, between two chambers containing KCl solutions representing extracellular and intracellular fluids. These two chambers are connected via agar salt bridges to a 3MKCl compartment, into which voltmeter leads are connected via Ag/AgCl wires. Replacement of the external KCl solution to a series of lower concentrations causes a membrane potential of negative polarity for the cation selective membranes and positive polarity for the anion selective membranes. The shifts in membrane potentials were corrected for liquid junction potentials and fit to the Planck equation using ion activities, in order to quantify the relative potassium to chloride permeabilities (PK:PCl). Our preliminary analysis in cationic membranes gave an averaged PK:PCl of 42.4 ± 4.4 (5 membranes, mean ± SEM). Two important experimental points relate to thorough solution exchange, and being aware of rapid voltage drifts due to KCl concentration changes in the unstirred layers. In bionic experiments, a positive intracellular potential was recorded when the external solution was replaced by NaCl, indicating the membranes show some selectivity for K+ over Na+. Our results provide a biophysical framework to support the use of these artificial membranes to simulate cell physiology mechanisms in undergraduate teaching.