We have shown that the absorption of tetraphenylborate into black lipid membranes formed from either bacterial phosphatidylethanolamine or glycerolmonooleate produces concentration-dependent changes in the electrostatic potential between the membrane interior and the bulk aqueous phases. These potential changes were studied by a variety of techniques: voltage clamp, charge pulse, and "probe" measurements on black lipid membranes; electrophroetic mobility measurements on phospholipid vesicles; and surface potential measurements on phospholipid monolayers. The magnitude of the potential changes indicates that tetraphenylborate absorbs into a region of the membrane with a low dielectric constant, where it produces substantial boundary potentials, as first suggested by Markin et al. (1971). Many features of our data can be explained by a simple three-capacitor model, which we develop in a self-consistent manner. Some discrepancies between our data and the simple model suggest that discrete charge phenomena may be important within these thin membranes.

The charge-pulse technique is applied to a study of valinomycin-mediated potassium transport across glycerol monooleate (GMO) bilayers. The theory, based on the Läuger-Stark model, is developed for the steady-state domain. The voltage dependences of the surface complexation reactions are also considered. The analysis of the data yields the folowing values for the rate constants: (see article). With the exception of this last ratio, all the values agree well with previously published data. The implication of the exponential term, 0.045, is that the plane of reaction for the surface complexation actually occurs a small distance within the membrane dielectric. If one presumes that the reaction plane is about half way between the plane of adsorbed complex and the membrane-water interface, one deduces that the complex "feels" only about 80% of the applied voltage across the membrane.