title: Elasticity of the red cell membrane and its relation to hemolytic disorders: an optical tweezers study.
abstract: We have used optical tweezers to study the elasticity of red cell membranes; force was applied to a bead attached to a permeabilized spherical ghost and the force-extension relation was obtained from the response of a second bead bound at a diametrically opposite position. Interruption of the skeletal network by dissociation of spectrin tetramers or extraction of the actin junctions engendered a fourfold reduction in stiffness at low applied force, but only a twofold change at larger extensions. Proteolytic scission of the ankyrin, which links the membrane skeleton to the integral membrane protein, band 3, induced a similar effect. The modified, unlike the native membranes, showed plastic relaxation under a prolonged stretch. Flaccid giant liposomes showed no measurable elasticity. Our observations indicate that the elastic character is at least as much a consequence of the attachment of spectrin as of a continuous membrane-bound network, and they offer a rationale for formation of elliptocytes in genetic conditions associated with membrane-skeletal perturbations. The theory of Parker and Winlove for elastic deformation of axisymmetric shells (accompanying paper) allows us to determine the function BH(2) for the spherical saponin-permeabilized ghost membranes (where B is the bending modulus and H the shear modulus); taking the literature value of 2 x 10(-19) Nm for B, H then emerges as 2 x 10(-6) Nm(-1). This is an order of magnitude higher than the value reported for intact cells from micropipette aspiration. Reasons for the difference are discussed.
authors.affiliation: MRC Unit of Muscle and Cell Motility, Randall Institute, Kings College London, 26-29 Drury Lane, London WC2B 5RL, United Kingdom. john@muscle.rai.kcl.ac.uk
authors.forename: J
authors.initials: J
authors.lastname: Sleep
authors.forename: D
authors.initials: D
authors.lastname: Wilson
authors.forename: R
authors.initials: R
authors.lastname: Simmons
authors.forename: W
authors.initials: W
authors.lastname: Gratzer
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D004548:Elasticity; D004910:Erythrocyte Membrane / Q000737:chemistry*; D006461:Hemolysis / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D008081:Liposomes; D008560:Membrane Fluidity; D008565:Membrane Proteins / Q000097:blood / Q000737:chemistry; D008954:Models, Biological; D055095:Optics and Photonics; D010766:Phosphorylation; D013314:Stress, Mechanical
chemical_list: D008081:Liposomes; D008565:Membrane Proteins