Fig. 1. Calcium signaling during excitation-contraction coupling. Calcium signaling plays an essential role in cardiac muscle contraction and relaxation. Ca2+ entry via LTCC triggers SR Ca2+ release through RyR, a process termed calcium-induced calcium release (CICR). CICR causes activation of contraction of myofilaments. SR Ca2+ uptake via SERCA2a and extrusion via NCX allow relaxation of myofilaments. CICR, Ca2+-induced Ca2+ release; LTCC, L-type Ca2+ channel; NCX, Na+-Ca2+ exchanger; PLB, phospholamban; RyR, ryanodine receptor; SERCA2a, sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 2a; SR, sarcoplasmic reticulum; T-tubule, transverse tubule.
