Figure 1.

Simplified schematic diagram of Ca²⁺ regulation channels during the myocardial cell contraction and relaxation phases. The sarcoendoplasmic reticulum calcium ATPase (SERCA-ATPase) pump is vital for absorbing Ca²⁺ and storing it in the sarcoplasmic reticulum (SR). This absorption reduces the Ca²⁺ concentration in cytoplasm, contributing to the initiation of the myocyte’s relaxation phase. Importantly, SERCA-ATPase remains active throughout the relaxation process. In parallel, ryanodine receptors (RyR), stimulated by external Ca²⁺ from L-type Ca²⁺ channels, release stored Ca²⁺ from the SR. This increases the concentration of Ca²⁺ in the cytoplasm, ultimately triggering myocyte contraction.