Effect of reversible osmotic stress on live cell plasma membranes, probed via Laurdan general polarization measurements

Here we seek to gain insight into changes in the plasma membrane of live cells upon the application of osmotic stress using Laurdan, a fluorescent probe that reports on membrane organization, hydration, and dynamics. It is known that the application of osmotic stress to lipid vesicles causes a decrease in Laurdans generalized polarization (GP), which has been interpreted as an indication of membrane stretching. In cells, we see the opposite effects, as GP increases when the osmolarity of the solution is decreased. This increase in GP is associated with the presence of caveolae, which are known to disassemble and flatten in response to osmotic stress, in a process that supplies extra plasma membrane in physiological processes. SignificanceCells can experience multiple stresses in vivo. Furthermore, the application of osmotic stress is used as a biophysical tool to interrogate membrane proocesses in vitro. We sought to investigate the consequences of osmotic stress on the plasma membrane properties using the fluorescent probe Laurdan. Unexpectedly, we find that osmotic stress leads to an increase in GP in live cells. The opposite change in GP has been observed in model lipid bilayers, reminding us there are limitations to the utility of model systems in understanding cell membrane behavior. Despite years of research, the cell membrane still has ways to surprise us.