Cholesterol Solubility Threshold of Polyunsaturated Membranes

Cholesterol is a crucial component of cell membranes as it influences the membrane\u27s properties and function. The purpose of this research is to estimate the cholesterol solubility threshold (CST) of polyunsaturated membrane. Depending on the phospholipid (PL), cholesterol has a different affinity to the PL membrane. Once the membrane is saturated with Chol, the excess cholesterol that is no longer incorporated within the membrane is excluded outside the membrane-forming cholesterol crystals (CHCs). The concentration at which these CHCs begin to form is known as the CST. Here, we investigated 1-palmitoyl-2-arachidonoyl -sn-glycero-3-phosphocholine (PAPC) membrane with cholesterol concentration ranging from 0 to 75 mol% using differential scanning calorimetry (DSC). To preserve compositional homogeneity throughout the membrane suspension, we used the rapid solvent exchange (RSE) method to prepare the multilamellar vesicles (MLVs). Membrane suspensions were heated from 0 to 120 °C and the CHCs peak in DSC thermal scans were detected. CHCs present in the membrane suspensions give rise to the peaks in the thermal scans, which enable us to determine the CST of the membrane. We estimated the CST for the PAPC membrane to be ~ 43 mol%