A theoretical description of the kinetics of the passive transport of
both lipophobic and lipophilic nonelectrolytes, weak acids, and weak b
ases through membranes of large unilamellar vesicles is discussed. Equ
ations are derived which may be used to obtain permeability coefficien
ts and predict the extent of LW entrapment of permeant molecules. Theo
retical curves are generated to illustrate the difference between lipo
phobic and lipophilic permeation. By applying a diffusional approach r
ather than a simple first order kinetic approach to the problem of pas
sive transport, some of the inconsistencies observed in other works ar
e corrected. (C) 1998 Elsevier Science B.V.