Osmotic pressure induced pores in phospholipid vesicles.

We report a comparative study of the leadage of hydrophilic molecules from vesicles of egg lecithin (EL) and of dipalmitoyllecithin (DPL). The effect of osmotic pressure differences a leakage is consistent with a model for statistical pore nucleation process. The major difference in osmotic pressure induced leakage from DPL and EL is that the number of pore creation sites is much greater in DPL. We suggest that the difference in number of these sites also accounts for other differences in the properties of DPL and EL, namely for differences in vesicle fusion and apparent rate of "flip-flop".