Question

Calcium is released and sequestered differently in Skeletal and Cardiac muscles. Why are the differences important physiologically in relation to the purpose of those types of muscles?

Answer 1

The calcium is important ion that is required for both skeletal and cardiac muscle contraction. The SR or sarcoplasmic reticulum in the muscles is known to store the calcium ion through calcium pumps and when released are known for contraction and functioning of these muscles. When it receives a stimulus, the SR releases the calcium which binds to troponin that undergoes shape change and hence removes the tropomyosin from the site of the binding. In the skeletal muscles, the source of the Ca2+ coupling is the SR or sarcoplasmic reticulum but in case of cardiac muscle, the coupling Ca2+ is from its contact with extracellular concentration of Ca2+. When the calcium is released in the skeletal muscle it leads to the interaction between the actin and myosin. The binding sites of the myosin is exposed that bind and forms cross bridges with actin and hence helps in the contraction of the muscle. With the calcium induced calcium release, it helps in the contraction of the cardiac muscle. As the calcium is released it leads to initiation of the smooth muscle contraction in the cardiac muscle through binding of calmodulin and leads to activation of the myosin light chain kinase enzyme. There are receptors for the Calcium induced calcium release within the cardiac cells called as cardiomyocyte that binds to the calcium during depolarization and hence releases more calcium ions within the cells.