Aspiration of THP1 into a micropipette. Mechanical deformation of monocytic THP-1 cells: occurrence of two sequential phases with differential sensitivity to metabolic inhibitors

Blood leukocytes can exhibit extensive morphological changes during their passage through small capillary vessels. The human monocytic THP-1 cell line was used to explore the metabolic dependence of these changes in shape. Cells were aspirated into micropipettes for determination of the rate of protrusion formation. They were then released and the kinetics of morphological recovery was studied. Results were consistent with Evans’ model (Blood 64:1028, 1984) of a viscous liquid droplet surrounded by a tensile membrane. The estimated values of cytoplasmic viscosity and membrane tension were 162 Pa.s and 0.0142 mN/m respectively. The influence of metabolic inhibitors on cell mechanical behavior was then studied: results strongly suggested that deformation involved two sequential phases. The cell elongation rate measured during the first 30 s following the onset of aspiration was unaffected by azide, an inhibitor of energy production, and it was about doubled by cytochalasin D, a microfilament inhibitor, and colchicine, a microtubule inhibitor. However, during the following 2 min, deformation was almost abolished in cells treated with azide and cytochalasin D, whereas the protrusion of control cells exhibited an approximately threefold increase in length. It is concluded that, although cells seemed to deform as passive objects, active metabolic processes were required to allow extensive morphological changes triggered by external forces.