Intrinsic material properties of the erythrocyte membrane indicated by mechanical analysis of deformation

Deformation of the erythrocyte membrane by the micropipette technique permits analysis of intrinsic material characteris- tics of the membrane and provides a means to differentiate purely membrane factors from such extrinsic factors as sur- face area-to-volume ratio. Using small micropipettes (<0.5 im radius) to deform cells, it is evident that the red cell mem- brane behaves like a solid for periods of time up to 5-10 mm of sustained deforma- tion; for long periods of strain, permanent deformations occur, indicative of the semi- solid structural character. In the time range in which the membrane behaves like a solid, the material is linearly elastic up to strains of 400%, implying a loose network structure in the membrane plane, and evaluation of the elastic parameterz (z for normal discocytes equals 7 x 1 0� dynes/ cm) suggests that the elements comprising the network may have a molecular weight of approximately that of the water-soluble membrane protein spectrin. Whether the network systemis cross-linked or simply a polymer solution remains unanswered. Experimental data indicate that plastic flow of the membrane under conditions of protracted strain may lead to permanent deformation of the membrane, whereas uniform dilation of the membrane, requir- ing over 1000 times more energy than for plastic flow, results in membrane failure and lysis. Analyses of the data from larger micropipettes of limiting mean cylindrical diameter show their utility in evaluating extrinsic factors, e.g., surface area-to- volume relationships, which are related to the capability of the whole cell to form a new configuration with implicit resistance to total surface area change, as the cell enters narrow channels of the microcircu- lation. Thus, micropipettes with diameters in the 2.7-3.O-jum range can provide sensi- tive comparisons of cellular deformability of erythrocytes. I NVESTIGATION OF THE basic mechanisms underlying hemolysis and fragmentation of erythrocytes, and the regulation of cell release from marrow have generally been limited to morphologic and biochemical studies that have yielded much important information despite the static nature of the observations. Physiologic studies have the increased significance of providing insight into the dynamics of behavior of blood cells, and, coupled with morpho- logic and biochemical approaches, may reflect important in vivo mechanisms. Obvious limitations include the fact that interpretations often are applicable to populations of cells, and the dynamics of single cells or cell components such as the membrane may not be easily derived. Recently a variety of approaches to analysis of the blood cell properties by