question: What is known as Calcium Induced Calcium Release (CICR) and its role in cardiomyocyte contractility?
answer: the cicr mechanism has been understood mainly based on binding of cytosolic ca(2+) with ryanodine receptors (ryrs) and inducing ca(2+) release from the sarcoplasmic reticulum (sr). l-type ca(2+) channels activate ryrs to produce cicr in smooth muscle cells in the form of ca(2+) sparks and propagated ca(2+) waves. in heart cells, a tight coupling between the gating of single l-type ca(2+) channels and ryanodine receptors (ryrs) underlies calcium release. the importance of ca-induced ca release in excitation-contraction coupling in the heart. waves of calcium-induced calcium release occur in a variety of cell types and have been implicated in the origin of cardiac arrhythmias. in mammals, ca(2+) influx as l-type ca(2+) current (ica) triggers the release of ca(2+) from sarcoplasmic reticulum (sr) and ca(2+)-induced ca(2+) release (cicr) is critical for excitation-contraction coupling. 