Biological cells use motors to affect motion and carry cargo. One of them we study is a specialized electric motor which uses the transmembrane potential across the membrane to produce polarization currents that change the length and diameter of outer hair cells found in the mammalian cochlea. A second more prevalent motor is the actin motor; cells use the chemical energy released upon polymerization of actin to push the leading edge of their cell membrane forward. It was predicted more than 30 years ago that cells may use the depolymerization of actin to pull or yank the cell membrane back. We report the first measurement of this pulling force in a living cell. We determine the force per working filament produced upon polymerization and depolymerization of actin, and show that the process is discrete and cooperative. Our data supports an end-tracking motor model that operates in both the forward and reverse directions. Linker proteins are required to attach the actin filaments to the membrane and serve as the transducers coverting converting the chemical energy to mechanical motion of the membrane. We show that actin polymerization and depolymerization decreases and increases membrane tension, and will affect biological processes that are sensitive to tension (e.g. exocytosis and endocytosis). Our objective is to further characterize the biophysics and biochemical components of this motor in cell models, hair cells, and transformed (cancer) cells.
Farrell B, Qian F, Kolomeisky AB, Anvari A, Brownell WE. 2010. Depolymerization of F-actin pulls the plasma membrane in a living cell. Submitted for publication.
Farrell B, Qian F, Anvari B, Brownell WE. 2010. Measurement of the stationary force of actin-filled membrane tubes in a living cell. In preparation.
Farrell B, Cox SJ. Estimating the time course of pore expansion during the spike phase of exocytotic release in mast cells of the beige mouse. Bull Math Biol 2002; 64: 979-1010.
Marszalek P, Farrell B, Verdugo P, Fernandez JM. Kinetics of serotonin release from single secretory vesicles: (I) Amperometric detection of 5-hydroxytryptamine from electroporated granules. Biophys J 1997;73:1160-1168.
Marszalek P, Farrell B, Verdugo P, Fernandez JM. Kinetics of serotonin release from single secretory vesicles: (II) Ion exchange gel regulates the release of 5-hydroxytryptamine from electroporated granules. Biophy J 1997;73:1169-83. (Joint first author)
Marszalek P, Farrell B, Fernandez JM. Ion exchange gel regulates neurotransmitter release through the exocytotic fusion pore. Soc Gen Physiol Ser 1996;51:211-22.