MUSCLE PHYSIOLOGY

Detailed explanation-1: -When calcium binds to troponin, the troponin changes shape, removing tropomyosin from the binding sites. The sarcoplasmic reticulum stores calcium ions, which it releases when a muscle cell is stimulated; the calcium ions then enable the cross-bridge muscle contraction cycle.

Detailed explanation-2: -During relaxation, calcium has to be detached from troponin and expelled out of the cell or stored back inside the sarcoplasmic reticulum. Figure 2-A heart muscle cell and its components. Calcium enters the cell through “doors” called ion channels, and interacts with various components of the cell.

Detailed explanation-3: -Released calcium ions bind to the troponin complex (consisting of troponin I, troponin T, and troponin C) to change their conformation and result is contraction [146]. Contractile proteins (myosin and actin) and regulatory proteins (tropomyosin and troponin complex) are structural parts of the sarcomere.

Detailed explanation-4: -Contraction of heart muscle is driven by an interaction between myosin, actin and MgATP that is controlled on a beat-to-beat basis by transient binding of Ca2+ ions to the troponin/tropomyosin complex in the actin-containing thin filaments (Tobacman, 1996; Gordon et al.