Excitation Contraction Coupling Of Vascular Smooth Muscle Cell

Question 1

In summary, How is contraction triggered in smooth muscle cells? (5)

Answer 1

1. Ca2+ enters cytosol
2. Binds to CaM (calmodulin)
3. CaM activates MLCK (myosin light chain kinase)
4. MLCK phosphorylates light chain on myosin head
5. Allows myosin actin interactions, contraction occurs

Question 2

What two ways is the cystolic [ca2+] increased in smooth muscle cells?

Answer 2

Depolarisation opens voltage gates calcium channels

Noradrenaline activates alpha 1 receptors (adrenoreceptors)

Question 3

How does noradrenaline acitvating alpha 1 receptors on smooth muscle cells cause an increase in cystolic calcium con?

Answer 3

Receptor coupled with Gq protein.

Gq converts PIP2 into IP3

IP3 interacts with receptors on SR

Calcium is released

Question 4

What enzyme dephophorylates the myosin light chain in smooth muscle cells?

Answer 4

MLCP - myosin light chain phosphatase (always active)

Question 5

MLCP is always active. How can it be stopped from dephosphorylating all the myosin light chains in smooth muscles cells?

Answer 5

By PKC (protein kinase C)

Which is stimulated by DAG which comes as a product of the PIP2 conversion into IP3

Question 6

What can inhibit MLCK and how?

Answer 6

PKA (protein kinase A) inhibits MLCK by phosphorylating it

Question 7

What state must a myosin light chain be in in order to interaction with actin to cause contraction in smooth muscle cells?

Answer 7

Phosphorylated (by MLCK)