Mechanical Properties of Bovine Lens Cortical Membranes: A Study Using Atomic Force Microscopy
Abstract
The mammalian eye lens comprises densely packed older fiber cells in the center, called the nucleus, surrounded by a softer layer of younger fiber cells called the cortex. The fiber cell plasma membrane of the eye lens constitutes lipids (sphingolipids and phospholipids), cholesterol, and intrinsic membrane proteins. The composition of the eye lens membrane lipids differs between species and changes over time with age, condition of the eyes, etc. In a two-year-old bovine eye lens, the cholesterol to phospholipid ratio is 0.7 and 1.9 in the cortical and nuclear membranes, respectively. As the cell membrane regulates the transport property and plays a vital role in maintaining the elasticity of the lens, the study of lens membrane properties is essential. We study the mechanical properties of bovine lens cortical membranes using atomic force microscopy (AFM). Using the monophasic extraction method, we extracted the total lipids (lipid plus cholesterol) from the bovine lens cortex. We prepared multilamellar vesicles (MLVs) using the rapid solvent exchange (RSE) method. Small unilamellar vesicles (SUVs) were obtained by probe tip sonication of MLVs and dispensed on the mica surface to prepare a supported lipid membrane (SLM) which we investigated by AFM. We obtained the membrane thickness by preparing partial bilayer membrane patches and the topographical image of a complete membrane. We collected the force curves in a complete SLM to access the membranes' mechanical properties. Using the extended region of the force curves, we obtained the membrane breakthrough force and estimated membrane compressibility modulus (KA) and Young's modulus (E).
Mechanical Properties of Bovine Lens Cortical Membranes: A Study Using Atomic Force Microscopy
The mammalian eye lens comprises densely packed older fiber cells in the center, called the nucleus, surrounded by a softer layer of younger fiber cells called the cortex. The fiber cell plasma membrane of the eye lens constitutes lipids (sphingolipids and phospholipids), cholesterol, and intrinsic membrane proteins. The composition of the eye lens membrane lipids differs between species and changes over time with age, condition of the eyes, etc. In a two-year-old bovine eye lens, the cholesterol to phospholipid ratio is 0.7 and 1.9 in the cortical and nuclear membranes, respectively. As the cell membrane regulates the transport property and plays a vital role in maintaining the elasticity of the lens, the study of lens membrane properties is essential. We study the mechanical properties of bovine lens cortical membranes using atomic force microscopy (AFM). Using the monophasic extraction method, we extracted the total lipids (lipid plus cholesterol) from the bovine lens cortex. We prepared multilamellar vesicles (MLVs) using the rapid solvent exchange (RSE) method. Small unilamellar vesicles (SUVs) were obtained by probe tip sonication of MLVs and dispensed on the mica surface to prepare a supported lipid membrane (SLM) which we investigated by AFM. We obtained the membrane thickness by preparing partial bilayer membrane patches and the topographical image of a complete membrane. We collected the force curves in a complete SLM to access the membranes' mechanical properties. Using the extended region of the force curves, we obtained the membrane breakthrough force and estimated membrane compressibility modulus (KA) and Young's modulus (E).