Structural studies on phosphatidylcholine-cholesterol mixed vesicles

Abstract

The homogeneous, single-walled phosphatidylcholine-cholesterol mixed vesicles were prepared by ultrasonic irradiation of egg phosphatidylcholine in the presence of various amounts of cholesterol in solution at 4 degrees under a nitrogen atmosphere followed by molecular sieve chromatography on a Sepharose 4B column. Physicochemical studies performed on these systems invluding sedimentation velocity, diffusion, partial specific volume, intrinsic viscosity, and trapped volume measurements allowed estimation of the weight-average vesicle weight, the vesicle shape, and bilayer membrane thickness of the binary mixture of phosphatidylcholine and cholesterol. Vesicle hydration was calculated using two different methods and the agreement between them was excellent up to cholesterol concentration of 0.32 mole fraction. It was observed that the structural parameters change slowly with increasing cholesterol content up to around 0.3 mole fraction and a relatively abrupt structural alteration occurs above this cholesterol content. This abrupt structural change is consistent with the asymmetrical distribution of lipid composition between the inner and outer bilayer face.

Cholesterol‐induced modulation of membrane hydration studies by thermal analysis

“…Yet, there is no clear picture of Ch-DPPC molecular interactions in the hydrated bilayers. Both the polar and the non-polar parts of DPPC molecules seem to be involved as shown by spectroscopic studies [1, 121. These results and those in [5,8] show that Ch incorporation into DPPC bilayers up to 1 S-25% mol/ mol enhances the bilayer hydration by 30-50% (flg.4). This enhancement of hydration is observed below 0°C (our results), over 540°C [5], and at 20°C ( [8] for egg lecithin).…”

“…Both the polar and the non-polar parts of DPPC molecules seem to be involved as shown by spectroscopic studies [1, 121. These results and those in [5,8] show that Ch incorporation into DPPC bilayers up to 1 S-25% mol/ mol enhances the bilayer hydration by 30-50% (flg.4). This enhancement of hydration is observed below 0°C (our results), over 540°C [5], and at 20°C ( [8] for egg lecithin). It is displayed for very concentrated multibilayers (our paper and [5]) as well as by sonicated dilute monolamellar suspensions [8].…”

“…We have used thermal analysis [6,7] (DSC differential scanning calorimetry) to measure directly the amount of water forming the interbilayer aqueous spacing in a multibilayer system. We apply this technique to the systems studied by other techniques such as the X-ray diffraction technique [5] and various dynamic techniques [8]. The agreement between our results and those in [5,8] are better than qualitative .…”

“…We apply this technique to the systems studied by other techniques such as the X-ray diffraction technique [5] and various dynamic techniques [8]. The agreement between our results and those in [5,8] are better than qualitative .…”

“…The results are shown in fig.4 as a function of bilayers composition. They are compared to the results reported in [5,8] for mixed or pure phospholipid multibilayers or monolamellar vesicles. The 3 sets of results confirm that low contents of cholesterol increase the bilayer hydration.…”