Question

in a laboratory experiment you have treated a muscle cell with a calcium channel blocker. the membrane still depolarizes, but the concentration of calcium never increases in the cytosol. which of the following describes what will happen next?
multiple choice
only one cross - bridge cycle will occur but no second cycle.
binding of myosin to actin will take place.
tropomyosin will continue to cover the myosin binding sites on actin and no cross - bridges will form.
a single twitch in skeletal muscle but no sustained contraction.
contraction will occur but the muscle will be stuck in the contracted state and unable to relax.

Explanation:

In muscle contraction, calcium ions bind to troponin, which causes a conformational change in the troponin - tropomyosin complex. This change exposes the myosin - binding sites on actin. When a calcium channel blocker is used and cytosolic calcium concentration doesn't increase, tropomyosin will continue to cover the myosin - binding sites on actin, preventing cross - bridge formation.

Answer:

Tropomyosin will continue to cover the myosin binding sites on actin and no cross - bridges will form.