The nature of the voltage-dependent conductance induced by alamethicin in black lipid membranes
- 236 Downloads
Alamethicin induces a conductance in black lipid films which increases exponentially with voltage. At low conductance the increase occurs in discrete steps which form a pattern of five levels, the second and third being most likely. The conductance of each level is directly proportional to salt concentration, inversely proportional to solution viscosity, and nearly independent of voltage.
The probability distribution of the five steps is not a function of voltage, but as the voltage is increased, more levels begin to appear. These can be explained as super-positions of the original five, both in position and relative probability.
This suggests that the five levels are associated with a physical entity which we call a pore. This point of view is confirmed by the following measurements. The kinetic response of the current to a voltage step is first order, and shows an exponential increase in rate of pore formation and an exponential decrease in rate of pore disappearance with voltage. If these rates are statistical, the number of pores should fluctuate about a voltage-dependent mean. High conductance current fluctuations are too large to be explained by fluctuation in the number of pores alone. But if fluctuations among the five levels are included, the magnitude of the fluctuations at high conductance is accurately predicted.
Alamethicin adsorbs reversibly to the membrane surface, and the conductance at a fixed voltage depends on the ninth power of alamethicin concentration and on the fourth power of salt concentration, in the aqueous phase. In our bacterial phosphatidyl ethanolamine membranes, alamethicin added to one side of the membrane produces elevated conductance only when the voltage on that side is increased.
KeywordsSalt Concentration High Conductance Ethanolamine Phosphatidyl Ethanolamine Solution Viscosity
Unable to display preview. Download preview PDF.
- Bamberg, G., Laüger, P. 1973. Channel formation kinetics of gramicidin A in lipid bilayer membranes.J. Membrane Biol. 11:177Google Scholar
- Boheim, G. H. 1972. Erregbarkeit Schwarzer Lipid-Membranen. Thesis RWTH, Aachen, GermanyGoogle Scholar
- Cherry, R. J., Chapman, D., Graham, D. E. 1972. Studies of the conductance changes induced in bimolecular lipid membranes by alamethicin.J. Membrane Biol. 7:325Google Scholar
- Eisenberg, M. 1972. Voltage Gateable Ionic Pores in Black Lipid Membranes Induced by Alamethicin. Ph.D. Thesis. California Institute of Technology, Pasadena, CaliforniaGoogle Scholar
- Hauser, H., Finer, E. G., Chapman, D. 1970. Nuclear magnetic resonance studies of the polypeptide alamethicin and its interaction with phospholipids.J. Mol. Biol. 53:4AGoogle Scholar
- Hille, B. 1970. Ionic channels in nerve membranes.In: Progress in Biophysics and Molecular Biology. J. A. V. Butler, Editor. Vol. 21, p. 1. Pergamon Press, Oxford and New YorkGoogle Scholar
- Hodgkin, A. L., Huxley, A. F. 1952. Quantitative description of membrane current and its application to conduction and excitation in nerve.J. Physiol. 117:550Google Scholar
- Huebner, J., Bruner, L. J. 1972. Apparatus for measurements of the dynamic current-voltage characteristics of membranes.J. Phys. E. Sci. Instrum. 5:310Google Scholar
- Johnson, M. 1973. Structure and Function of Alamethicin. Ph.D. Thesis. Northwestern University, Evanston, IllinoisGoogle Scholar
- Lüttgau, H.-C. 1958. Sprunghafte Schwankungen unterschwelliger Potentiale an markhaltigen Nervenfasern.Z. Naturf. 13b:692Google Scholar
- McMullen, A. I., Marlborough, D. I., Bayley, P. M. 1971. The conformation of alamethicin.F.E.B.S. 16:278Google Scholar