Electromechanical coupling and regulation of force of cardiac contraction

Cardiac muscle fibres, like skeletal muscle fibres, are divided into sarcomeres, the basic unit of contraction. The contractile elements include actin, myosin, tropomyosin and troponin. The myosin molecules are arranged into thick filaments, while the actin molecules form the basis of the thin filaments. The troponin and tropomyosin are attached to the thin filaments as in skeletal muscle. In contrast to fast skeletal muscle fibres, which need to produce repetitive mechanical action only for short periods before resting, and hence can accrue an oxygen debt, cardiac muscle fibres need to perform repetitive activity for long periods (a lifetime) without rest. Consequently, cardiac muscle fibres are much more dependent on the utilization of oxygen and have an abundance of mitochondria, with rapid oxidation of substrates and formation of ATP, needed for mechanical contraction. © 2006.