A basis of echinocytosis and stomatocytosis in the disc-sphere transformations of the erythrocyte.

Abstract

A mechanism of erythrocyte shape control has been previously hypothesized in which Band 3, the anion exchange protein, controls the shape. In essence, the mechanism hypothesizes that the membrane skeleton is used to generate different shapes and the alternate influx and efflux of anions mediated by Band 3, which recruit Band 3 to an inward-facing and an outward-facing conformation, contract and relax the skeleton by folding and unfolding spectrin. Spectrin is bound to Band 3 by the intermediary of ankyrin. The mechanism is shown to be consistent with rapid shape deformations of the erythrocyte in blood circulation. We have examined whether the mechanism could provide a basis of echinocytosis and stomatocytosis in disc-sphere transformations of the erythrocyte induced by a wide variety of agents. These agents were classified into four groups: lipids of the bilayer, Donnan equilibrium modifiers, Band 3 anion transport inhibitors and integral membrane protein modifiers. Evidence is presented that the lipids play a secondary function in the control of the erythrocyte shape, as indicated by the mechanism. Two possible functions of the lipids are suggested with respect to the mechanism. Without exception, echinocytogenic and stomatocytogenic Donnan equilibrium modifiers decrease and increase the equilibrium ratio of chloride (Cl-(i)/Cl-(o)), respectively, as predicted by the mechanism. Echinocytosis produced by competitive anion transport inhibitors slowly transported inward by Band 3 and by affinity labels of Band 3 is compatible with the mechanism. Evidence is presented which indicates that echinocytosis and stomatocytosis induced by amphiphilic drugs and detergents occur by inhibition of the Band 3 anion transport. Finally, echinocytosis and stomatocytosis induced by non-covalent and covalent modifiers of integral membrane proteins such as agglutinins and digestive enzymes are consistent with the mechanism.