Surface potential determination in planar lipid bilayers: A simplification of the conductance-ratio method |
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| Affiliation: | 1. Faculty of Chemistry and Biochemistry, Molecular Biochemistry, Ruhr University Bochum, Universitätstrasse 150, D-44780 Bochum, Germany;2. Centre for Membrane Pumps in Cells and Disease—PUMPKIN, Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg C, Denmark;3. Department of Biochemistry, Weill Cornell Medical College, 1300 York Avenue, New York, NY 10065, USA;1. Dipartimento di Fisica, Università Sapienza, P.le A. Moro 5, 00185 Roma, Italy;2. Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy;3. Dipartimento per l''Innovazione dei sistemi Biologici, Agroalimentari e Forestali, Università degli Studi della Tuscia, Via San Camillo de Lellis s.n.c., 01100 Viterbo, Italy;4. Banca del Germoplasma della Tuscia, Università degli Studi della Tuscia, Largo dell''Università s.n.c., 01100 Viterbo, Italy;5. Dipartimento di Chimica, Università degli Studi di Milano, Via Golgi 19, 20133 Milano, Italy;6. CNR-IPCF UOS Roma, Dipartimento di Fisica, Università Sapienza, P.le A. Moro 5, 00185 Roma, Italy;7. Center for Life Nanoscience@Sapienza, Istituto Italiano di Tecnologia, V.le Regina Elena, 291, 00185 Rome, Italy;1. Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College st, Toronto, ON M5S3M2, Canada;2. Institute for Medical Physics and Biophysics, University of Leipzig, Leipzig, Germany |
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| Abstract: | One of the methods available for the measurement of surface potentials of planar lipid bilayers uses the conductance ratio between a charged and a neutral bilayer doped with ionophores to calculate the surface potential of the charged bilayer. We have devised a simplification of that method which does not require the use of an electrically neutral bilayer as control. The conductance of the charged bilayer is measured before and after the addition of divalent cations (Ba2+) to the bathing solution. Ba2+ ions screen fixed surface charges, decreasing the surface potential. If the membrane is negatively charged the screening has the effect of decreasing the membrane conductance to cations. The resulting conductance ratio is used to calculate the surface potential change, which is fed into an iterative computer program. The program generates pairs of surface potential values and calculates the surface charge density for the two conditions. Since the surface charge density remains constant during this procedure, there is only one pair of surface potentials that satisfies the condition of constant charge density.Applying this method to experimental data from McLaughlin et al. [McLaughlin, S.G.A., Szabo, G. and Eisenman, G., Divalent ions and the surface potential of charged phospholipid membranes, J. Gen. Physiol., 58 (1971) 667–687.] we have found very similar results. We have also successfully used this method to determine the effect of palmitic acid on the surface potential of asolectin membranes. |
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