Fig. 1.

Role of NCX in cellular Ca²⁺ cycling during excitation-contraction coupling in cardiac myocytes. During the action potential Ca²⁺ enters the myocyte via the voltage dependent sarcolemmal L-type Ca²⁺ channel, and thus triggers further Ca²⁺ release from the sarcoplasmic reticulum via sarcoplasmic Ca²⁺ release channels (ryanodine receptors). The released Ca²⁺ diffuses towards the myofilaments and induces the contraction. During diastole Ca²⁺ is shifted back into sarcoplasmic reticulum by the Ca²⁺ ATPase of the sarcoplasmic reticulum (SERCA). The Na⁺/Ca²⁺ exchanger extrudes Ca²⁺ from the cytosol into the extracellular space.