Permeability of bimolecular membranes made from lipid extracts of human red cell ghosts to sugars

Summary

Spherical lipid bimolecular membranes of a large surface area separating two aqueous solutions were formed from the total lipid extracts of human red cell ghosts and from their individual lipid components. The isotopic permeabilities of these membranes to biologically important sugars and to a related polyol were measured. The observedd-glucose permeabilities of the bimolecular membranes of the total lipid, phosphatidyl choline, phosphatidyl ethanolamine, sphingomyelin, and cholesterol were 2.35, 2.51, 2.23, 1.35, and 0.62×10⁻¹⁰ cm/sec, respectively. These permeabilities are about four to five orders of magnitude lower than that of the intact red cell membrane. The permeabilities of the bimolecular membrane made from an identical extract of the total lipid to different sugars varied: the values ford-glucose,d-mannose,d-ribose,d-fructose, 2-deoxy-d-glucose, 3-0-methyl-d-glucose, andd-mannitol were 2.3, 2.6, 8.9, 0.38, 16.1, 11.2, and 0.44×10⁻¹⁰ cm/sec, respectively. The pattern of the difference is neither parallel with nor as extensive as that observed with the intact red cell membrane. The observed permeabilities of the lipid membranes, however, agree qualitatively with what is predicted by an analysis of non-specific movements of nonelectrolytes across the cell membranes. The failure of the membrane lipids to reproduce the carrier function in a structure most closely approximating that of living membranes strongly suggests that some membrane components other than lipids are required for this function.