  A recently described technique (Estes and Mayer, Biochim. Biophys. Acta 1712
(2005) 152--160) for the preparation of giant unilamellar vesicles (GUVs) in
solutions with high ionic strength is examined. By observing a series of
osmotic swellings followed by vesicle bursts upon a micropipette transfer of a
single POPC GUV from a sucrose solution into an isoosmolar glycerol solution, a
value for the permeability of POPC membrane for glycerol, P = (2.09+/-0.82) x
10^{-8} m/s, has been obtained. Based on this result, an alternative mechanism
is proposed for the observed exchange of vesicle interior. With modifications,
the method of Estes and Mayer is then applied to preparation of flaccid GUVs.
