Sourcebook of Laboratory Activities in Physiology Ion permeability of artificial membranes evaluated by diffusion potential and electrical resistance measurements

Shlyonsky V. Ion permeability of artificial membranes evaluated by diffusion potential and electrical resistance measurements. Adv Physiol Educ 37: 392–400, 2013; doi:10.1152/advan.00068.2013.—In the present article, a novel model of artificial membranes that provides efficient assistance in teaching the origins of diffusion potentials is proposed. These membranes are made of polycarbonate filters fixed to 12-mm plastic rings and then saturated with a mixture of creosol and n-decane. The electrical resistance and potential difference across these membranes can be easily measured using a low-cost volt-ohm meter and home-made Ag/AgCl electrodes. The advantage of the model is the lack of ionic selectivity of the membrane, which can be modified by the introduction of different ionophores to the organic liquid mixture. A membrane treated with the mixture containing valinomycin generates voltages from 53 to 25 mV in the presence of a 10-fold KCl gradient (in to out) and from 79 to 53 mV in the presence of a bi-ionic KCl/NaCl gradient (in to out). This latter bi-ionic gradient potential reverses to a value from 9 to 20 mV when monensin is present in the organic liquid mixture. Thus, the model can be build stepwise, i.e., all factors leading to the development of diffusion potentials can be introduced sequentially, helping students to understand the quantitative relationships of ionic gradients and differential membrane permeability in the generation of cell electrical signals.