Mechanical Properties of the Model of Pig Lens Lipid Membrane

The pig lens membrane is primarily composed of four different phospholipids (PLs): phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, and sphingomyelin, with phosphatidylcholine being the most abundant. Cholesterol is an important sterol found in the pig lens membrane where the cholesterol to phospholipid ratio (Chol/PL) is ~1 and ~2 in the cortical and nuclear membrane, respectively. We studied the mechanical properties of a model pig lens membrane with a Chol/PL mixing ratio of 0 and 1 using atomic force microscopy (AFM). We found that the supported pig lens model membrane of Chol/PL ratio 0 displayed two phases: solid ordered phase ( s _o ) and liquid disordered phase ( l _d ); the height difference between these two phases was approximately 1 nm. The membrane of Chol/PL mixing ratio 1 had only one phase, liquid ordered phase ( l _o ). We obtained two different breakthrough forces for the membrane of Chol/PL mixing ratio of 0 with an average value of 15.49±2.8 nN and 4.83±0.31 nN, related to s _o and l _d , respectively. The membrane of Chol/PL mixing ratio 1 with only one phase, l _o , had an average break through force of 10.62±0.39 nN. The elasticity of the membrane, quantified by the area compressibility modulus (K _A ), of the membrane with Chol/PL mixing ratio 1 was obtained as 1060±230 mN/m.