The Linear Motor in the Human Neutrophil Migration

The kinematics and dynamics of human neutrophils in a narrow glass tube (4.9 mu m to 6.3 mu m in diameter) have been investigated both experimentally and theoretically. Cells were activated by the tri-peptide (fMLP) to migrate through a tube with a mean speed of 0.15 +/- 0.03 mu m/s (54 activated cells). When a hydrostatic pressure was applied across the cell, the mean speed of the cell leading front linearly decreases when the pressure is increased. At a pressure difference of 1530 +/- 140 Pa (9 activated cells), the cell was forced to stop. The cell migration has been approximated by a tractor-trailer model. The cellular motor (leading front), the tractor, produced a traction force by converting chemical energy into mechanical work. This motor has been characterized as a linear motor with two machine coefficients: (i) the maximum traction T-o (37.7 nN) at V = 0, where V is the cellular speed (ii) the maximum cellular speed V-max (0.15 mu m/s). A characteristic time of approximately 100 s was measured for the action cycle of the linear motor. A phenomenological description of the chemotactic machine has been presented.