Smooth Muscle

Question 1

Outline the four steps that lead to smooth muscle contraction

Answer 1

1) Increase in Ca2+ levels as an action potential arrive
2) free Ca binds to Calmodulin
3) Ca-Calmodulin complex activates Myosin Light Chain Kinase (MLCK)
4) MLCK phosphorylates MLC on the myosin which leads to cross bridge formation with actin

Question 2

What are the two main mechanisms that act to increase intracellular Calcium?

Answer 2

L-type voltage gated Ca channels
Intracellular stores of Ca in the Sarcoplasmic reticulum, when receptors on this membrane are activated the Ca can be released.

Question 3

What are the two main mechanisms that act to decrease intracellular Calcium?

Answer 3

The ATP dependent Ca pump

The Na-Ca exchanger uses the Na gradient to transport Ca out of the cell.

Question 4

What effect does increase in cAMP have on vascular smooth muscle?

Answer 4

increase in cAMP results in relaxation of smooth muscle. The cAMP inhibits MLCK thus reducing phosphorylation of MLC

Question 5

What effect does increase in NO levels have on vascular smooth muscle?

Answer 5

NO activates guanylyl cyclase which increases cGMP. The cGMP activates a kinase which inhibits Calcium entry, activates K channels and decreases IP3

Question 6

What substances can cause the constriction of bronchial smooth muscle?

Answer 6

ACh acting on M3 mACh receptors
Leukotrienes C4 and D4
Histamine acting on the H1 receptor

Question 7

What substances can cause the relaxation of bronchial smooth muscle?

Answer 7

Salbutamol acting on Beta 2 receptors

Methylxanthines (caffeine) used in asthmatics