Measurement of erythrocyte membrane bilayer separation forces using fluorescence imaged magnetic tweezers

A mechanically stable association between the membrane bilayer and the underlying membrane associated skeleton is important for maintaining the integrity of the plasma membrane. This is particularly true for red blood cells, which must maintain their physical integrity and deformability within the dynamic environment of the vasculature. To probe the molecular mechanisms that account for membrane stability, we have combined a magnetic force transducer with fluorescence imaged microdeformation to measure the forces required to separate the membrane bilayer by pulling thin lipid cylinders, or tethers, off of the cell surface and observed the response of integral membrane proteins to bilayer separation. The results from these experiments indicate that, over a period of up to 30 minutes, the tethering force decreases until it reaches an equilibrium value of 54.7±8.3 pN while the surface density of fluorescently labeled integral proteins on the cell body is increased after tether formation