Cation control of erythrocyte membrane shape: Ca ++ reversal of discocyte to echinocyte transition caused by Mg ++ and other cations

Abstract

White erythrocyte membranes, or ghosts, were monoconcave discocytes when incubated in 50mM N-tris (hydroxymethyl) methyl-2-aminoethane sulfonic acid titrated to pH 7.4 with triethanolamine. If 3mM MgCl 2 was included in the incubation medium, the ghosts were predominantly echinocytes. The echinocytic form could also be induced by Co ++, Ni ++, Li +, Na +, K +, NH 4 + and tetramethylammonium ion, all as chloride salts. The concentration of cation necessary for 50% of the ghosts to be echinocytes was correlated with the hydrated charge density of the cation with the most highly charged cations being the most effective. The cations Ca ++, Sr ++, Ba ++ and La +++, (also as chloride salts) did not induce the normal echinocytic form, but at high levels induced a few misshapen forms with some resemblance to echinocytes. Instead Ca ++, Sr ++, Ba ++ and La +++ suppressed the formation of echinocytes in the presence of Mg ++ and other ions. This suggests the presence of a specific Ca ++ binding site important to shape control in the erythrocyte membrane.