Chaotropic anions and the surface potential of bilayer membranes.

The chaotropic anions perchlorate and thiocyanate adsorb to artificial phospholipid membranes. The negative electrostatic potential they produce at the surface of the membranes was measured by two independent techniques. The conductance produced by neutral carriers of cations and anions was measured to estimate changes in the surface potentials of planar black lipid films and the electrophoretic mobility of phospholipid vesicles was used to monitor changes in the zeta potentials of spherical bilayer membranes. Qualitatively similar results were obtained with the two techniques. The results, moreover, agreed with the change in surface potential produced by these anions at an air water interface, as measured directly with an ionizing electrode (Randles, J. E. B. (1957) Discuss. Faraday Soc. 24, 194-199). The results obtained with artificial bilayers may explain the observation (Wieth, J. O. (1970) J. Physiol. 207, 581-609) that thiocyanate increases the sodium or potassium and decreases the sulfate permeability of erythrocyte membranes.