Ion and sugar permeabilities of lecithin bilayers: Comparison of curved and planar bilayers

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Abstract
Na+ and sugar permeabilities of egg lecithin bilayers were measured using curved bilayers and planar bilayers as represented by single-bilayer vesicles and black lipid films, respectively. The Na+ permeability coefficient measured with single-bilayer vesicles at 25°C is (2.1±0.6)×10−13 cm sec−1. Because of technical difficulties it has been impossible to measure ionic permeabilities of values lower than about 10−10 cm sec−1 in planar (black) lipid bilayers using tracer methods. Thed-glucose andd-fructose permeabilities were measured with both curved and planar bilayers. The permeability coefficients measured with vesicles at 25°C are (0.3±0.2)×10−10 cm sec−1 for glucose and (4±1)×10−10 cm sec−1 ford-fructose; these are in reasonable agreement with the corresponding values obtained for planar (black) lipid bilayers which are (1.1±0.3)×10−10 cm sec−1 ford-glucose and (9.3±0.3)×10−10 cm sec−1 ford-fructose, respectively.