Modeling leakage kinetics from multilamellar vesicles for membrane permeability determination: application to glucose

The glucose permeability of bilayers formed from phosphatidylcholine, Brij30, and sodium octadecyl sulfate has been determined via an enzymatic reaction. Glucose is encapsulated in either uni- or multilamellar vesicles (MLV) and its concentration in the dispersion medium is monitored by spectrophotometry analysis through the rate of glucose oxidase-catalyzed reaction of glucose oxidation. A kinetic model of leakage, taking explicitly into account one, two, or n(w)-walls (n(w) >> 1) for the vesicles and assuming an enzymatic Michaelis-Menten behavior, is proposed and used to fit the experimental data. The two-wall model was chosen to fit experimental data obtained on MLV since an average value of 1.7 bilayers was estimated for MLV by cryo-TEM imaging. A permeability value of 5.8 +/- 4.4 10(-9) cm/s was found. The proposed model is validated by the measurement of the bilayer permeability deduced from the modeling of glucose leakage from unilamellar vesicles with the same composition. In this latter case, a value of 8.3 +/- 0.7 10(-9) cm/s is found for the permeability, which is within the error bar of the value found with MLV.