valinomycin and potassium-nitrate

Pyranine was incorporated into sonicated unilamellar vesicles of soybean phosphatidylcholine to monitor changes in the internal pH of the vesicles. Dilution of soybean phosphatidylcholine vesicles loaded with 0.3 M KCl, KNO3 or K2SO4 into salt-free buffer resulted in rapid exchange of K+ and protons. A pseudoequilibrium distribution of ions was achieved, since addition of valinomycin, uncoupler or nigericin now caused a rapid alkalinization of the vesicle interior. Dilution into buffer containing NaCl gave a further exchange of Na+ and protons following the initial K+/proton exchange. Na+ permeation was slower than that of K+. A stable membrane potential was not generated by the ion movements. It is proposed that aqueous channels are formed through the phospholipid bilayers and that K+ and Na+ permeate through these channels as the hydrated ions.

Topics: Arylsulfonates; Cations; Coloring Agents; Glycine max; Hydrogen-Ion Concentration; Ion Channels; Liposomes; Membrane Potentials; Nigericin; Nitrates; Particle Size; Phosphatidylcholines; Potassium; Potassium Chloride; Potassium Compounds; Protons; Salicylanilides; Sodium; Sulfates; Valinomycin