2023 Undergraduate Research Showcase

Document Type

Student Presentation

Presentation Date


Faculty Sponsor

Dr. Daniel Fologea and Dr. Rosey Whiting


In this work, we report on the effects of hypoosmotic stress, cholesterol depletion, and pore-forming toxin on physical properties of membranes, such as lipid order and fluidity. To achieve our goals, we employed Red Blood Cells as model membranes, and Laurdan as a solvato-chromic indicator of the membrane state. The generalized polarization function of Laurdan’s fluorescence was measured in different environmental conditions, and the experimental data were interpreted in terms of changes in lipid order and fluidity as previously reported for lipid membranes undergoing temperature-induced phase transitions. Our experiments indicate that hypoosmotic stress leads to a reduced lipid order and increased fluidity of the membrane, with a sharp transition between the two states. Controlled depletion of cholesterol in the membranes by exposure to Methyl-beta-cyclodextrin also indicates the role played by cholesterol in the ordering of the lipids, permeability, and general stability. Exposure of membranes to the pore-forming toxins Streptolysin O and lysenin also leads to decreased lipid order and increased fluidity, which we explained by the hydrophobic mismatch between the membrane’s core and inserted proteins.