- Excitation-contraction (EC) coupling in the contractile myocardium of cardiac muscle involves the depolarization of the cell membrane, which leads to the opening of voltage-gated L-type calcium channels.
- This allows for an influx of extracellular calcium into the cell, triggering the release of calcium from the sarcoplasmic reticulum through ryanodine receptors.
- The released calcium then binds to troponin C, leading to a conformational change in the troponin-tropomyosin complex and exposing the myosin-binding sites on actin.
- This allows for the formation of cross-bridges between actin and myosin, leading to the sliding of filaments and muscle contraction.
- In cardiac muscle, EC coupling is similar to skeletal muscle in that it involves the binding of calcium to troponin C to initiate muscle contraction.
- However, in cardiac muscle, the duration of the action potential is much longer, leading to a longer contraction time and a more sustained force of contraction.
- Additionally, the source of calcium for EC coupling in cardiac muscle is both extracellular and intracellular, whereas in skeletal muscle, it is primarily from the sarcoplasmic reticulum.
- Furthermore, cardiac muscle has a specialized structure called the intercalated disc, which allows for the rapid conduction of action potentials between cells, ensuring coordinated contraction of the heart.