Question

Contraction of skeletal muscle and smooth muscle cells both involve Ca2+ ions. How does the use of Ca differ between the two cell types?

Answer 1

Smooth muscle contraction is triggered by extracellular Ca2+ ions binding to calmodulin, activating myosin kinase. In skeletal muscle, Ca2+ ions from the sarcoplasmic reticulum bind to troponin and tropomyosin, exposing actin-binding sites.

Step-by-step explanation:

Smooth muscle contraction is triggered by the influx of extracellular Ca2+ ions, which diffuse into the sarcoplasm and bind to calmodulin. This activates an enzyme called myosin kinase, which phosphorylates myosin heads and allows them to interact with actin, leading to muscle contraction.

On the other hand, skeletal muscle contraction involves the release of Ca2+ ions from the sarcoplasmic reticulum (SR) upon an action potential. These Ca2+ ions bind to proteins called troponin and tropomyosin, which expose binding sites on actin for myosin heads.