Dynamic light scattering study of calcium-induced fusion in phospholipid vesicles

Acidic sonicated phospholipid vesicles can undergo dramatic morphological changes due to fusion in the presence of divalent metal ions. For example, small spherical phosphatidylserine vesicles can form scroll-like cylinders which precipitate in the presence of Ca²⁺ above a threshold concentration. Subsequent addition of EDTA will yield large, unilamellar vesicles. These events have previously been established through the combined use of differential scanning calorimetry and freeze-fracture electron microscopy. We have applied the technique of dynamic light scattering to follow these fusion events rapidly, accurately, and non-perturbatively as they occur in solution at calcium concentrations slightly below threshold for precipitation.