Bioelectrochemistry and Bioenergetics, 12 (1984) 405-412 A section of J. Electroanal. Chem., and constituting Vol. 173 (1984) Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands 405 zyxwvutsrqpo 637 bis-THE DIFFUSIVE PERMEABILITY OF BILAYER MEMBRANES THE CONTRIBUTION OF TRANSIENT AQUEOUS PORES * JAMES C. WEAVER **, KEVIN T. POWELL and ROBERT A. MINTZER l ** Harvard- MIT Division of Health Sciences and Technology, Cambridge, MA 02139 (U.S.A.) STEVEN R. SLOAN * Departments of Electrical Engineering and Computer Science, and Biology, MIT, Cambridge, MA 02139 (U.S.A.) HA0 LING ** Departments of Electrical Engineering and Computer Science, and Physics, MIT, Cambridge, MA 02139 (U.S.A.) (Revised manuscript received March 16th 1984) SUMMARY The diffusive permeability P,,, of various bilayer membranes has been measured by others. For small hydrophyllic solutes an important general feature is the rapid decrease in Pd,,, with increasing molecular size. As discussed in the preceding paper, the hypothesis of a large population of thermally excited transient aqueous pores is consistent with important electrical properties of bilayer membranes. Here the pore population is shown to also be consistent with experimentally determined diffusive permeabihties. In addition, the contribution of a pore population to Pd, is shown to give a significant fractional increase in membrane permeability as the transmembrane voltage is varied from 0 to 200 mV. Even though the magnitude of Pd,,, at U = 0 decreases rapidly with increasing molecular size, the fractional increase in Pdm with voltage is predicted to become larger as molecular size increases, and is believed to be related to the tremendous transient increase in permeability which accompanies reversible electrical breakdown. INTRODUCTION As mentioned in the previous paper, there have been a great number of previous studies on bilayer membranes. Of these, several have been directed towards de- * Presented at the 7th International Symposium on Bioelectrochemistry, Stuttgart (F.R.G.), 18-22 July 1983. l * To whom correspondence should be addressed at: 20A-128, M.I.T., Cambridge, MA 02139, U.S.A. l ** Present address: Department of Physics, University of Chicago, Chicago, IL, U.S.A. * Present address: Medical School, New York University, New York, NY, U.S.A. ** Present address: Department of Electrical Engineering, University of Illinois, Urbana, IL, U.S.A. 0302-4598/84/$03.00 0 1984 Elsevier Sequoia S.A.