Influence of Ca2+ and ethanol on the aggregation and thermal phase behaviour of l-dihexadecylphosphatidylcholine liposomes

✍ Scribed by Anu Kõiv; Paavo K.J. Kinnunen

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 648 KB
• Volume: 62
• Category: Article
• ISSN: 0009-3084
• DOI: 10.1016/0009-3084(92)90062-t

✦ Synopsis

The influence of Ca 2+ and ethanol on vesicle aggregation and thermal phase behaviour of the diether lipid 1,2-dihexadecylphosphatidylcholine (DHPC) was studied by light absorbance and DSC. At temperatures below the pretransition the ethanolinjected vesicles of L-DHPC were rapidly aggregated by Ca 2÷. Upon raising the cation concentration a biphasic increase in aggregation saturating at an approximate [Ca2+]/[lipid] ratio of 1.5:1 was observed. Further increase in [Ca 2÷] up to [Ca2+]/[lipid] stoichiometries exceeding 2.5:1 led to the loss of aggregation. Removal of ethanol by dialysis abolished Ca2+-induced aggregation. Ethanol-injected vesicles of the ester-linked L-dipalmitoylphosphatidylcholine (L-DPPC) or the racemic DL-DHPC were not aggregated by Ca 2+ thus indicating the importance of the absence of ester carbonyls as well as the stereochemical configuration of the lipid in determining the mode of interaction of DHPC with Ca 2+. Differential scanning calorimetry of multilamellar liposomes of L-DHPC showed an increase by 8 ° in the pretransition temperature Tp in the presence of 250 mM ethanol. Both with and without ethanol, increasing concentrations of Ca 2+ corresponding to [Ca2+]/[lipid] ratios of 1:1 to 20:1 caused a gradual decrease in Tp and finally the disappearance of the pretransition. Concomitantly a slight elevation in T m occurred. No principal differences were observed in the thermal phase behaviour of the L-isomer and racemic DL-DHPC.