Shape transformations of giant unilamellar vesicles induced by ethanol and temperature variations

The shape transformations of giant unilamellar vesicles (GUVs) of dimyristoylphosphatidylcholine (DMPC) in water/ethanol solutions were investigated as a function of temperature (18-43 degrees C) and ethanol content (0-40 vol%). GUVs were prepared by electroformation and their shapes were monitored by phase-contrast microscopy furnished with an image-recording set-up. Two systems were compared: (1) GUVs formed in presence of ethanol; and (2) GUVs preformed in distilled water with ethanol added subsequently. In the first case, GWs in the gel state are typified by a multifaceted, irregular shape that transforms into a smooth, rounded shape with increase of temperature. This transformation is reversible and takes place at about or below 24 degrees C. It coincides in temperature with the DMPC gel-liquid crystalline phase transition in the respective water/ethanol solutions. The effect of ethanol added to GUVs preformed in distilled water is strikingly different. The temperature of the multifaceted (folded)-to-smooth shape transformation first increases from 24 to 37 degrees C with increase of ethanol content up to 10 vol%, then decreases back to 24 degrees C upon further increase of ethanol up to 40 vol%. The reversal point of this biphasic effect at 10 vol% of ethanol coincides with that for formation of DMPC interdigitated phase. The shape transformations are reversible with a temperature hysteresis of 2-3 degrees C. They are rather cooperative and take place in a narrow range of less than 0.2 degrees C at temperatures that remain constant for times of up to 15 h. (C) 1999 Elsevier Science B.V. All rights reserved.