Osmotic swelling of unilamellar vesicles by the stopped-flow light scattering method. Elastic properties of vesicles

Abstract

Unilamellar vesicles of l-α-dimyristoylphophatidylcholine have been prepared by the ether injection technique. Gel filtration on Sephacryl S1000 was used to obtain fractions of narrow polydispersity, of radius from 300 to 600 Å. Dynamic light scattering was used to determine the change in size of these vesicles in response to an osmotic pressure drop, and its dependence on vesicle size. The amplitude of swelling ( ΔR/ R) is linearly proportional to the osmotic pressure difference across the bilayer. We have determined the elastic area stretching modulus using a theory of membrane elasticity: it depends on the vesicle radius in the range of size studied. Vesicles having radius smaller than 400 Å show little or no swelling.