Cortical tension

Pasternak, C., Spudich, J.A., Elson, E.L. (1989). Capping of surface receptors concomitant cortical tension are generated by conventional myosin. Nature 341, 549-551. 

Rac- and Rho-type GTPases can regulate the formation of protrusive lamel-lipodia, and cell retraction as well as cortical tension. Several local signaling networks have been identified that in a hierarchical way control cell shape and migration [5]. 

L6vtrup and Hansson Mild (1981) Sharp maximum in cortical tension of amphibian eggs 16... 

EgeUioff, T.T., Naismith, T.V. and Brozovich, F.V. (1996). Myosin-based cortical tension in Dictyostelium resolved into heavy and light chain-regulated components./. Muscle Res. Cell Motil. 17, 269-274. 

The membrane deformation is calculated from observed macroscopic changes in cell geometry, usually with the use of simple geometric shapes to approximate the cell shape. The membrane force resultants are calculated from force balance relationships. For example, in the determination of the area expansivity modulus of the red cell membrane or the cortical tension in neutrophils, the force resultants in the plane of the membrane of the red cell or the cortex of the white cell are isotropic. In this case, as long as the membrane surface of the cell does not stick to the pipette, the membrane force resultant can be calculated from the law of Laplace ... 

The early observations of Bagge et al. [1977] led them to suggest that the neutrophil behaves as a simple viscoelastic solid with a Maxwell element (an elastic and viscous element in series) in parallel with an elastic element. This elastic element in the model was thought to pull the unstressed cell into its spherical shape. Subsequently, Evans and Kukan [1984] and Evans and Yeung [1989] showed that the cells flow continuously into a pipette, with no apparent approach to a static limit, when a constant suction pressure was applied. Thus, the cytoplasm of the neutrophil should be treated as a liquid rather than a solid, and its surface has a persistent cortical tension that causes the cell to assume a spherical shape. 

Using a micropipette and a small suction pressure to aspirate a hemispherical projection from a cell body into the pipette, Evans and Yeung measured a value for the cortical tension of 0.035 mN/m. Needham and Eiochmuth [1992] measured the cortical tension of individual cells that were driven down a tapered pipette in a series of equilibrium positions. In many cases the cortical tension increased as the cell moved further into the pipette, which means that the ceU has an apparent area expansion modulus (Equation 60.7). They obtained an average value of 0.04 mN/m for the expansion modulus and an extrapolated value for the cortical tension (at zero area dilation) in the resting state of 0.024 mN/m. The importance of the actin cytoskeleton in maintaining cortical tension was demonstrated by Tsai et al. [ 1994]. Treatment of the cells with a drug that disrupts actin filament structure (CTB = cytochalasin B) resulted in a decrease in cortical tension from 0.027 to 0.022 mN/m at a CTB concentration of 3 /rM and to 0.014 mN/m at 30 /rM. 

Preliminary measurements in one of our laboratories (RMH) indicate that the value for the cortical tension of a monocyte is about double that for a granulocyte, that is, 0.06 mN/m, and the value for a lymphocyte is about 0.035 mN/m. 

The existence of a cortical tension suggests that there is a cortex — a relatively thick layer of F-actin filaments and myosin — that is capable of exerting a finite tension at the surface. If such a layer exists, it would have a finite thickness and bending rigidity. Zhelev et al. [1994] aspirated the surface of neutrophils into pipettes with increasingly smaller diameters and determined that the surface had a bending modulus of about 1 to 2 X 10 J, which is 5 to 50 times the bending moduli for erythrocyte or lipid bilayer membranes. The thickness of the cortex should be smaller than the radius of smallest pipette used in this study, which was 0.24 fjtra. 

Using their model of the neutrophil as a Newtonian liquid drop with a constant cortical tension and (as they showed) a negligible surface viscosity, Yeung and Evans [1989] analyzed the flow of neutrophils... 

An alternative attempt to account for the initial rapid entry of the ceU into micropipettes involved the application of a Maxwell fluid model with a constant cortical tension. Dong et al. [1988] used this model to analyze both the shape recovery of neutrophils following small, complete deformations in pipettes and the small-deformation aspiration of neutrophils into pipettes. Another study by Dong et al. [1991], they used a finite-element, numerical approach and a Maxwell model with constant cortical tension to describe... 

Cortical tension Analogous to surface tension of a liquid drop, it is a persistent contractile force per unit length at the surface of a white blood ceU. (Units 1 mN/m = 1 dyn/cm)... 

Evans, E. and Yeung, A. 1989. Apparent viscosity and cortical tension of blood granulocytes determined by micropipet aspiration. Biophys. J. 56 151-160. 

Herant, M., Heinrich, V. and Dembo, M. (2005) Mechanics of neutrophil phagocytosis behavior of the cortical tension. Journal of Cell Science, 118, 1789-97. 

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