Figure 4.

A schematic of the effect of hyperkalemia and prolonged myocardial membrane depolarization on Na⁺ entry through the “window current” and the net influx of Ca²⁺ into the myocardial cell via the reversal of the Na⁺/Ca²⁺ exchanger [3Na⁺ ions are extruded in exchange for 1 Ca²⁺ entry (Bers and Despa, 2009) at a membrane potential of −50 mV (Baczko et al., 2003)]. Global or regional ischemia and metabolic acidosis impact further on Ca²⁺ loading, with increases in intracellular H⁺ further activating the Na⁺/H⁺ exchanger (Avkiran, 2001) resulting in 1Na⁺ ion being exchange for 1 H⁺ ion. The diagram was adapted from Bers and colleagues (Bers et al., 2003; Bers and Despa, 2006).