Membrane transport of anandamide through resealed human red blood cell membranes

The use of resealed red blood cell membranes (ghosts) allows the study of the transport of a compound in a nonmetabolizing system with a biological membrane. Transmembrane movements of anandamide (N-arachidonoylethanolamine, arachidonoylethanolamide) have been studied by exchange efflux experiments at 0 degrees C and pH 7.3 with albumin-free and albumin-filled human red blood cell ghosts. The efflux kinetics is biexponential and is analyzed in terms of compartment models. The distribution of anandamide on the membrane inner to outer leaflet pools is determined to be 0.275 +/- 0.023, and the rate constant of unidirectional flux from inside to outside is 0.361 +/- 0.023 s(-1). The rate constant of unidirectional flux from the membrane to BSA in the medium ([BSA]o) increases with the square root of [BSA]o in accordance with the theory of an unstirred layer around ghosts. Anandamide passed through the red blood cell membrane very rapidly, within seconds. At a molar ratio of anandamide to BSA of <1, membrane binding of anandamide increases with increasing temperatures between 0 degrees C and 37 degrees C, and the equilibrium dissociation constants are in the nanomolar range. The nature of membrane binding and the mechanism of membrane translocation are discussed.