Monensin induced suicidal erythrocyte death.

Eryptosis, the suicidal erythrocyte death, is characterized by cell membrane scrambling and cell shrinkage. Eryptosis may be triggered by excessive hyperosmotic or isosmotic cell shrinkage leading to increase of cytosolic Ca2+ concentration. Eryptosis is further stimulated by the K+ ionophore valinomycin, which leads to exit of KCl and osmotically obliged water, or by energy (glucose) depletion, which compromises the function of the Na+/K+ ATPase thus increasing cytosolic Na+ concentration. The present study explored whether the Na+ ionophore monensin affects erythrocyte cell volume and eryptosis. The cell membrane scrambling was estimated from binding of annexin V to phosphatidylserine at the erythrocyte surface, cell volume from forward scatter in FACS analysis, cytosolic Ca2+ concentration from Fluo3 fluorescence and the cytosolic ATP concentration from a luciferase-based assay. Within 24 hours, exposure to monensin (0.1-10 µg/ml) significantly increased forward scatter, cytosolic Ca2+ concentration and annexin V-binding. Glucose depletion was followed by decreased forward scatter and increased cytosolic Ca2+ concentration and annexin V-binding. The effect on forward scatter was partially reversed, the effect on cytosolic Ca2+ concentration and annexin V binding augmented by additional treatment with monensin. In conclusion, monensin dissociates the alterations of cell membrane and cell volume in suicidal erythrocyte death.