Figure 1.

Calcium Cycling in the Cardiac Myocyte. Arrows represent Ca²⁺ flux during one contractile cycle. A) Action potential allows Ca²⁺ entry through the LTCC, which B) triggers a much larger Ca²⁺ release from the SR through the RyR. C) Ca²⁺ binds to myofilament proteins, leading to force production. D) Ca²⁺ is then taken back up into the SR via SERCA2a, or E) pumped out of the cell via NCX. S100A1 and PLN act as modulators of Ca²⁺ transport protein function. Parv buffers Ca²⁺ away from myofilaments after force production.