Accumulation of free cytosolic Ca2+ appears to be a key
pathophysiological process underlying the development of the
death-associated processes in rat erythrocytes (Fig. 5). Causative
role of elevated Ca2+ concentration for NaF-induced cytotoxicity
was shown in vitro in the human epithelial lung cells
[31], rat renal tubular cells [32], and thymocytes [33]. In
erythrocytes, rise of intracellular Ca2+ activity due to activation
of Ca2+ channels or inhibition of Ca2+ pump stimulates Ca2+-
sensitive K+ channels resulting in the exit of KCl and cell
shrinkage, triggers phospholipid scrambling in the plasma
membrane leading to PS exposure at outer membrane leaflet,
and activates protease calpain with consequent proteolysis of
the structural cytoskeletal proteins such as spectrin [34–36].
Our works [15, 37] also show that NaF considerably enhances
Ca2+ intake in the rat erythrocytes in vitro followed by Ca2+-
dependent K+ loss and cell shrinkage. This study established
for the first time that F-induced accumulation of Ca2+ in
erythrocytes occurs under in vivo conditions.