Polymerisation of red cell membrane protein contributes to spheroechinocyte shape irreversibility

Abstract

THE discocyte–spheroechinocyte transformation of red cells undergoing ATP depletion and calcium accumulation is reversible after restoration of normal ATP and calcium levels or exposure of cells to stomacytogenic agents such as cationic anaesthetics^1–3. This transformation becomes irreversible after a prolonged incubation without glucose or an introduction of high calcium concentrations into the cells.⁴ In our studies of membrane protein composition of metabolically depleted red cells, we have noted that aerobically ATP-depleted erythrocytes contained a >1 × 10⁶-dalton reducible membrane protein polymer which was selectively enriched in spectrin, the major protein at the cytosol membrane interface⁵. We suggested that the formation of this complex was due to changes in the assembly of spectrin in ATP-depleted red cell membranes to form closer contacts, allowing a spontaneous crosslinking of the nearest spectrin neighbours through disulphide couplings⁵. Another polymer differing from that in ATP-depleted red cells by an absence of cleavage with reducing agents was recently noted in fresh red cells, into which Ca²⁺ (>0.5 mM) was introduced by ionophore A23187 (ref. 6); it has been attributed to a crosslinking of γ-glutamyl ε-lysine residues of spectrin and other membrane proteins, catalysed by a Ca²⁺-activated cytoplasmic transglutaminase^6,7. As both the above membrane protein polymers were found in cells which transformed into spheroechinocytic shape, we have studied and report here results which show that such spontaneous membrane protein crosslinking contributes to a permanent fixing of the red cells to their abnormal shape.