concanavalin-a and Carcinoma-256--Walker

Capping in cells developing polarity has been reinterpreted on the basis of a quantitative analysis of Concanavalin A (Con A) redistribution and cell movement in Walker carcinosarcoma cells. Several new features emerged. Based on the developing asymmetry in the distribution of surface-bound Con A, the direction of cell movement and the prospective front-tail polarity can already be predicted when the cell is spherical. Development of polarity by an initially spherical cell is associated with formation of two parts. The concentrically contracting part (prospective uropod) characterized by surface-associated Con A decreases in size, while the other part is cleared from Con A and grows into formerly unoccupied space. Surface-bound Con A shows isotropic centripetal movement towards the initial position of the centroid of the spherical cell rather than rearward movement. Therefore, the centroid of fluorescence intensity remains either stationary or moves marginally forward with respect to the initial position of the spherical cell. The amount and direction of cell movement measured correlates closely with values predicted by a theoretical model that assumes a unidirectional transfer of volume from a stationary contracting compartment into a protruding compartment. The results suggest that isotropic (cortical) contraction of the initially spherical cells and one-sided relaxation rather than unidirectional retrograde movement of ligand-receptor complexes produces movement in cells developing polarity. Reversible accumulation of surface-bound Con A at the uropod occurring to a similar extent in untreated and colchicine-treated cells is partly due to membrane folding and partly to movement in the plane of the membrane.

Topics: Animals; Carcinoma 256, Walker; Cell Membrane; Cell Movement; Cell Polarity; Cell Size; Concanavalin A; Microscopy, Confocal; Microscopy, Video; Models, Biological; Tumor Cells, Cultured

We mimicked essential elements of the cortical-contraction model of cell locomotion by exposing Walker carcinosarcoma cells to passive deformation and to hydrostatic pressure changes within micropipettes followed by shape recovery after release. Protrusion, contraction and segregation of cell surface membrane components were observed. Regardless of the initial shape (spherical, polarized with lamellipodia or blebs) cells tended to produce blebs during uptake into the pipette and during and after release from the pipette, but usually not during the short time they were held within the pipette. Bleb formation depended on the deformation stress, extracellular hydrostatic pressure and cell structure (initial shape). In polarized cells, blebs were much more readily induced at the front as compared to the tail. Cells undergoing large deformations formed constriction rings and large hyaline caps. Deformation resulted in segregation of membrane components. Equatorial constriction rings divided the cell into two parts which differed with respect to Con A binding and their role in shape recovery. Spherical and polarized cells usually recover the respective initial shape. Polarized cells reacquired the same type of protrusions (blebs or lamellipodia) which they exhibited before deformation. Shape recovery of spherical cells was characterized by a rapid recoil by about 20% followed by a slow asymptotic recovery.

Topics: Animals; Carcinoma 256, Walker; Cell Membrane; Cell Size; Concanavalin A; Humans; Time Factors; Tumor Cells, Cultured