title: Dependency of delta pH-relaxation across vesicular membranes on the buffering power of bulk solutions and lipids.
abstract: The dependency of delta pH-relaxation kinetics across the membrane of sonicated small phospholipid vesicles on the concentration of internally entrapped buffer has been investigated by means of the pH-indicator dye pyranine. A very high contribution of lipid headgroups to the internal buffering power of the liposomes is observed, amounting to an equivalent phosphate buffer concentration of 110 mM. This localized two-dimensional proton/hydroxide ion reservoir must be considered in any determination of the H+/OH- permeability coefficient. Furthermore, it could have significance for energy-transduction across biological membranes. From the established linear relation between delta pH-relaxation rates and buffering power, net H+/OH- permeabilities of 3 X 10(-3) cm/s for soybean phospholipid (SBPL) and 1 X 10(-4) cm/s for diphytanoyl phosphatidylcholine (diphytanoyl PC) vesicles at pH 7.2 as well as buffering powers per lipid molecule of 6 X 10(-2) (pH-unit)-1 (SBPL) and 4 X 10(-2) (pH-unit)-1 (diphytanoyl PC) are calculated. In the case of diphytanoyl PC vesicles, delta pH-decay is accelerated by the presence of chloride ions.
mesh_terms: D001190:Arylsulfonates; D002021:Buffers; D004058:Diffusion; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides; D007700:Kinetics; D008081:Liposomes; D008433:Mathematics; D008564:Membrane Potentials; D008954:Models, Biological; D011522:Protons; D012996:Solutions; D013816:Thermodynamics; D014634:Valinomycin
chemical_list: D001190:Arylsulfonates; D002021:Buffers; D006878:Hydroxides; D008081:Liposomes; D011522:Protons; D012996:Solutions; D014634:Valinomycin; C005047:pyranine