Torocyte membrane endovesicles induced by octaethyleneglycol dodecylether in human erythrocytes

Endovesicles induced in human erythrocytes by octaethyleneglycol dodecyleth er (C12E8) were studied by confocal laser scanning microscopy, using fluore scein isothiocyanate dextran as a nonspecific fluid marker. The endovesicle s appeared to consist mainly of a ring-formed toroidal part joined with a c entral flat membrane segment. The torocyte contour length was several mu m There was usually one torocyte endovesicle per cell. The endovesicles seeme d to be located near the cell surface. In sections of C12E8-treated erythro cytes transmission electron microscopy revealed the frequent occurrence of flat membrane structures with a bulby periphery, which apparently ave cross sections of torocyte endovesicles. The possible physical mechanisms leadin g to the observed torocyte endovesicle shape are discussed. The torocyte en dovesicles seem to be formed in a process in which an initially stomatocyti c invagination loses volume while maintaining a large surface area. Because intercalation of C12E8 in the erythrocyte membrane induces inward membrane bending (stomatocytosis) we assume that C12E8 is preferentially located in the inner lipid layer of the erythrocyte membrane, i.e., in the outer lipi d layer of the endovesicle membrane. It is suggested that local disturbance s of the lipid molecules in the vicinity of the C12E8 molecules in the oute r lipid layer of the endovesicle membrane form membrane inclusions with the effective shape-of an inverted truncated cone. If the interaction between the inclusion and the membrane is weak, the membrane of such an endovesicle can be characterized by its negative spontaneous curvature, which may lead to a torocyte endovesicle shape with a small relative volume. Effects of a possible strong interaction between the C12E8-induced membrane inclusions and the membrane on the stability of the torocyte endovesicles are also ind icated.