Calculation of a gap restoration in the membrane skeleton of the red bloodcell: Possible role for myosin II in local repair

Human red blood cells contain all of the elements involved in the formation of nonmuscle actomyosin II complexes (V. M. Fowler. 1986. J. Cell. Biochem . 31:1-9; 1996. Curr. Opin. Cell Biol. 8:86-96). No clear function has yet been attributed to these complexes. Using a mathematical model for the stru cture of the red blood cell spectrin skeleton (M. J. Saxton. 1992. J. Theor . Biol. 155:517-536), we have explored a possible role for myosin II bipola r minifilaments in the restoration of the membrane skeleton, which may be l ocally damaged by major mechanical or chemical stress. We propose that the establishment of stable links between distant antiparallel actin protofilam ents after a local myosin II activation may initiate the repair of the disr upted area. We show that it is possible to define conditions in which the c alculated number of myosin II minifilaments bound to actin protofilaments i s consistent with the estimated number of myosin II minifilaments present i n the red blood cells. A clear restoration effect can be observed when more than 50% of the spectrin polymers of a defined area are disrupted. It corr esponds to a significant increase in the spectrin density in the protein fr ee region of the membrane. This may be involved in a more complex repair pr ocess of the red blood cell membrane, which includes the vesiculation of th e bilayer and the compaction of the disassembled spectrin network.