MICROANATOMY

Detailed explanation-1: -Troponin plays a central role in the calcium-regulation of muscle contraction: Troponin is the sole calcium-binding component of thin filaments (actin-tropomyosin-troponin complex) of striated muscles. Thin filaments without troponin support contraction irrespective of calcium concentration.

Detailed explanation-2: -(2) Calcium binds to troponin C, which induces a conformational change in the troponin complex. This causes tropomyosin to move deeper into the actin groove, revealing the myosin-binding sites.

Detailed explanation-3: -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.

Detailed explanation-4: -Troponin is shown in red (subunits not distinguished). Upon binding calcium, troponin moves tropomyosin away from the myosin-binding sites on actin (bottom), effectively unblocking it.