Proton and hydroxide ion permeability of phospholipid vesicles.

Abstract

The apparent permeability of H+ through phospholipid bilayers was determined by measuring H+ efflux from large unilamellar phospholipid vesicles with internal space buffered at pH 4. The value obtained is .apprx. 10-9 cm/s at room temperature, 5 orders of magnitude lower than was recently reported for the combined permeability for H+ and OH- [Nichols et al, (1980)]. The apparent permeability measured in this way is the sum of contributions from the movement of H+ and of uncharged species (HCl or HNO3) in equilibrium with anions in the solution. There is evidence that the uncharged species make the dominant contribution and that the permeability coefficient for H+ per se is no larger than 5 .times. 10-12 cm/s. An attempt to measure OH- permeability by use of vesicles buffered at pH 10 did not give a conclusive result because the vesicle walls appeared to be damaged by exposure to this pH. An apparent permeability coefficient of .apprx. 10-7 cm/s was estimated for undamaged membranes.