An animal with aortic valve insufficiency got hypertrophy of its left heart ventricle. Some of its parts have local contractures. What substance accumulated in the myocardiocytes caused these contractures?

Answer options

1. Potassium
2. Lactic acid
3. Calcium
4. Sodium
5. Carbon dioxide

Explanation

Calcium prolongs the duration of muscle cell depolarization before repolarization occurs. Contraction in cardiac muscle occurs due to the binding of the myosin head to adenosine triphosphate (ATP), which then pulls the actin filaments to the center of the sarcomere, the mechanical force of contraction. Myofibril activity is required for muscle contraction on the molecular level. When ATP binds to myosin, it separates from the actin of the myofibril, which causes a contraction. Muscle contraction is a complex process regulated by calcium influx and the stimulus of electrical impulses.