Effect of intra- and extra-liposomal distribution of sodium chloride on the stability of large unilamellar vesicles.
Three groups of 1,2-dipalmitoyl-rac-glycero-3-phosphocholine (DPPC) large unilamellar vesicle (LUV) dispersions were studied: LUV (A) dispersions with only extraliposomal sodium chloride (NaCl), LUV (B) dispersions with intra- and extraliposomal NaCl, and LUV (C) dispersions with only intraliposomal NaCl. The NaCl concentrations ranged from 0 to 150 mM. An abrupt increase in leakage was observed around -10 degree C for all the three groups of LUV, which coincided with the temperature of extraliposomal ice formation. Within the three groups, leakage of LUV (C) was significantly higher than the other groups. Extraliposomal ice formation and the resulting freeze-concentration of LUV may be the major cause of the leakage. Intraliposomal ice formation observed at -43 degree C seemed to stop leakage of LUV when LUV were frozen below -43 degree C. An exotherm of eutectic crystallization of NaCl was occasionally observed at -37 degree C, with a higher probability of formation at 150 mM extraliposomal NaCl than at 50 mM. The eutectic crystals were thought to cause additional leakage from the LUV (B).
Siow
Lee Fong
LF
Department of Food Science, University of Otago, P. O. Box 56, Dunedin 9054, New Zealand.
Rades
Thomas
T
Lim
Miang Hoong
MH
D015925:Cryopreservation; D005615:Freezing; D012965:Sodium Chloride / Q000378:metabolism*; D053835:Unilamellar Liposomes / Q000378:metabolism*
D053835:Unilamellar Liposomes; D012965:Sodium Chloride