Reversible shape change of Triton-treated erythrocyte ghosts induced by Ca2+ and Mg-ATP

The shape of the human erythrocyte depends on intracellular ATP content and echinocytic erythrocyte ghosts obtained in the presence of Mg-ATP acquire a diskocytic shape after incubation at 37 degrees C; however, agreement is lacking about the molecular basis of the shape changes. The suggestion that phosphorylation of cytoskeletal structures underlying the membrane is involved has been disputed and alternative explanations based on lipid bilayer theory and metabolism of phospholipid have been proposed. Recently, we re-examined the effect of ATP on the shape of ghosts and found that it consists of two distinct steps. We have, therefore, now examined the effect of physiological concentrations of Ca2+ and ATP on the cytoskeleton of the erythrocyte membrane directly using Triton-treated ghosts which had lost this permeability barrier. Our findings suggest that a noncovalent effect of ATP on the cytoskeleton is a prerequisite for shape change.