MECHANICAL-PROPERTIES OF NEURONAL GROWTH CONE MEMBRANES STUDIED BY TETHER FORMATION WITH LASER OPTICAL TWEEZERS

Many cell phenomena involve major morphological changes, particularly in mitosis and the process of cell migration. For cells or neuronal gr owth cones to migrate, they must extend the leading edge of the plasma membrane as a lamellipodium or filopodium. During extension of filopo dia, membrane must move across the surface creating shear and flow. In tracellular biochemical processes driving extension must work against the membrane mechanical properties, but the forces required to extend growth cones have not been measured. In this paper, laser optical twee zers and a nanometer-level analysis system were used to measure the ne uronal growth cone membrane mechanical properties th rough the extensi on of fi loped ia-like tethers with IgG-coated beads. Although the pro bability of a bead attaching to the membrane was constant irrespective of treatment; the probability of forming a tether with a constant for ce increased dramatically with cytochalasin B or D and dimethylsulfoxi de (DMSO). These are treatments that alter the organization of the act in cytoskeleton. The force required to hold a tether at zero velocity (F-0) was greater than forces generated by single molecular motors, ki nesin and myosin; and F, decreased with cytochalasin B or D and DMSO i n correlation with the changes in the probability of tether formation. The force of the tether on the bead increased linearly with the veloc ity of tether elongation. From the dependency of tether force on veloc ity of tether formation, we calculated a parameter related to membrane viscosity, which decreased with cytochalasin B or D, ATP depletion, n ocodazole, and DMSO. These results indicate that the actin cytoskeleto n affects the membrane mechanical properties, including the force requ ired for membrane extension and the viscoelastic behavior.