CHOLESTEROL DOES NOT REMOVE THE GEL-LIQUID CRYSTALLINE PHASE-TRANSITION OF PHOSPHATIDYLCHOLINES CONTAINING 2 POLYENOIC ACYL CHAINS

Homoacid (single-acid) phosphatidylcholines containing two linoleate (18:2), arachidonate (20:4), or docosahexaenoate (22:6) chains were dispersed in water to form multilamellar vesicles. The influence of cholesterol on the gel to liquid phase transitions was studied by differential scanning calorimetry (DSC). The pure dipolyeoic phosphatidylcholines exhibited very broad endothermic transitions (widths of 28 to 38-degrees-C at scanning rates of 5-degrees-C/ min) in the temperature range of about -80-degrees-C to -30-degrees-C. The mixing of cholesterol into the phospholipids in proportions up to 50 mol% had little effect on the temperatures, widths or enthalpy changes associated with the phase transitions. The data suggest that cholesterol does not interfere with the packing of these lipids in the gel state, possibly because the packing is already irregular or because the solubility of cholesterol in these lipids is low, or both.