A light-scattering measurement of membrane vesicle permeability

Light-scattering/intensity autocorrelation measurements of vesicle diffusivity were used to follow the time course of the osmotic response of lobster abdominal sarcoplasmic reticulum vesicles to five lipophobic nonelectrolytes. Steady-state portions of the resulting time traces show these vesicles to be permeable to ethylene glycol and glycerol and impermeable to erythritol, glucose, and sucrose. Using measured values of the hydrodynamic radii of these nonelectrolytes, it is concluded that under passive transport conditions, these vesicles may be thought of as having pores whose radii lie between 3.1 and 3.5 A. In addition, the results presented here indicated that above a certain impermeable nonelectrolyte concentration, vesicles did not respond osmotically even though they had not collapsed. This suggests that at least under the experimental conditions reported here, vesicles behaved as if rigid when their average volume had decreased to about 50% of its original isotonic value.