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Describe the differences in actin/myosin regulation of, respectively, smooth and skeletal muscle and indicate the structural similarities in their respective contractile units. Explain why smooth muscles can develop and maintain force with a much lower rate of ATP hydrolysis than skeletal muscle. Distinguish between muscle relaxation from the contracted state and the phenomenon of stress relaxation and give examples of each process. Diagram the intracellular pathways that control contraction and…

Where are the two sources of Calcium for Smooth Muscle?

1. Calcium enters from the ECF.-Ca is relatively high outside the cell. and low in the cell. This works because smooth muscle is small..

2. Calcium enters intracellulary from the
sparce sarcoplasmic reticulum stores

What are three ways the smooth muscle cell can increase calcium concentration inside the cell?

1. Voltage-gated dihydropyridine receptors in the plasma membrane function as calcium channels.

2. iononotropic Receptor activated Calcium

3. Hormone linked G-coupled protein ligand receptors-uses 2nd messenger to release Ca inside the cell it self, Phospholipase C liberates DAG and IP3, and releases more calcium

What does calcium bind to in smooth muscle if it does not have troponin?

1. Calcium binds with calmodulin (4:1).
2. Calcium-calmodulin complex binds to
activates Myosin light chain kinase,
which in turn phosphorylates the Regulatory Light chain on myosin (1 ATP)
3. Phosphorylated myosin binds with actin.
Cross-bridge cycling can begin.

How does smooth muscle relaxation occur?

Calcium must be removed and the phosphate on the myosin must be removed via a phosphatase-which remove phosphate. Need to do both in order to get it stop.

Calcium is removed from the cell by the sarcolemmal
3 Na/Ca exchanger (3 Na come in 3 Ca go out)

We also pump Calcium into the sarcolemmal via the calcium ATPase.

Phosphatase C-effectively stops contraction.

What is the importance of myosin light chain phosphatase?

AKA phosphatase C

Functions to remove the phosphate on the myosin light chains

It is important to complete make the smooth muscle relax. The regulation is not fully understood.

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