[4] Since CICR is a positive-feedback system, it has been of great interest to elucidate the mechanism(s) responsible for its termination.
Excitation-contraction coupling in myocardium relies on sarcolemma depolarization and subsequent Ca2+ entry to trigger Ca2+ release from the sarcoplasmic reticulum.
CICR occurs when the resulting Ca2+ influx activates ryanodine receptors on the SR membrane, which causes more Ca2+ to be released into the cytosol.
[4][5] In cardiac muscle, the result of CICR is observed as a spatio-temporally restricted Ca2+ spark.
The result of CICR across the cell causes the significant increase in cytosolic Ca2+ that is important in activating muscle contraction.