Donnan equilibrium and pH gradient in isolated tracheal apical membrane vesicles
Langridge-Smith, J.E.; Dubinsky, W.P.
American Journal of Physiology 249(5 Pt 1): C417-C420
1985
ISSN/ISBN: 0002-9513 PMID: 4061628 Document Number: 253487
Apical plasma membrane vesicles isolated from bovine tracheal epithelium were found to possess both an electrical potential gradient (.DELTA.PSI.) and a transmembrane pH gradient (.DELTA.pH). The .DELTA.PSI. was calculated from the distribution of 86Rb+ in the presence of the ionophore valinomycin, and .DELTA.pH was determined from the distribution of [14C]methylamine under conditions of apparent equilibrium. Maximal values for .DELTA.PSI. of -54.3 .+-. 2.5 mV and for .DELTA.pH of 0.75 .+-. 0.07 pH units were obtained under low ionic strength conditions. Increasing the ionic strength by the addition of 50 mM of either permeant or impermeant electrolytes reduced .DELTA.PSI. to near zero values. The .DELTA.pH varied in parallel with the .DELTA.PSI. The results suggest that both 86Rb+ in the presence of valinomycin and H+ are in a Donnan equilibrium with impermeant negative charge in the vesicle interior.