Direct measures of large, anisotropic strains in deformation of the erythrocyte cytoskeleton

The erythrocyte's spectrin-actin membrane skeleton is directly shown to be capable of sustaining large, anisotropic strains. Photobleaching of an simi lar to 1-mu m stripe in rhodamine phalloidin-labeled actin appears stable u p to at least 37 degrees C, and is used to demonstrate large in-surface str etching during elastic deformation of the skeleton. Principal extension or stretch ratios of at least similar to 200% and contractions down to similar to 40%, both referenced to an essentially undistorted cell, are visually d emonstrated in micropipette-imposed deformation. Such anisotropic straining is seen to be consistent at a qualitative level with now classic analyses (Evans. 1973. Biophys. J. 13:941-954) and is generally nonhomogeneous thoug h axisymmetric down to the submicron scale. Local, direct measurements of s tretching prove quantitatively consistent (within similar to 10%) with inte grated estimates that are based simply on a measured relative density distr ibution of actin. The measurements are also in close agreement with direct computation of mean spectrin chain extension in full statistical mechanical simulations of a coarse-grained network held in a micropipette. Finally, a s a cell thermally fragments near similar to 48 degrees C, the patterned ph otobleaching demonstrates a destructuring of the surface network in a proce ss that is more readily attributable to transitions in spectrin than in F-a ctin.