Effect of cholesterol on liposome stability to ultrasonic disintegration and sodium cholate solubilization.

Liposome disintegration by either ultrasonic vibration or sodium cholate solubilization was investigated as a function of cholesterol (CH) content in the egg phosphatidylcholine (PC) liposome membrane. Turbidity changes were used as an indication of the membrane stability to these stresses. First-order disintegration constants (kufor ultrasonic stress and ksfor sodium cholate solubilization) were calculated to evaluate the membrane stability. A plot of ku against membrane CH content gave a sigmoidal curve on which inflection points occurred at about 15 mol% and 33 mol% CH. In contrast, the plot of ks against membrane CH content gave a biphasic curve with only one inflection point at about 17 mol% CH. These results can be explained in terms of the molecular