Hydroxyl ion permeability of lipid bilayer membranes.

The OH- permeability of lipid bilayer (egg phosphatidylcholine-cholesterol) membranes was estimated from ionic transference numbers and membrane conductances at high pH. Membranes are slightly cation (Na+) selective over the pH range of 6--10. However, at pH greater than 11, Na+ and Cl- conductances decrease and OH- conductance increases so that the membrane becomes highly selective to OH-. From the OH- conductance we estimate the OH- permeability coefficient to be 1.8 . 10(-9) cm . s-1. The OH- selectivity of lipid bilayers may contribute to the observed H+/OH- selectivity of some biological membrane at high pH.