Smooth muscle contraction

Question 1

What innervates smooth muscle?

Answer 1

ANS

Question 2

What neurotransmitter can be release from post-ganglionic nerves onto smooth muscles from the PNS?

Answer 2

Acetylcholine (Ach)

Question 3

What neurotransmitter can be released from post-ganglionic nerves onto smooth muscles from the Sympathetic NS?

Answer 3

Noradrenaline

Question 4

What neurotransmitter can be released from post-ganglionic nerves onto smooth muscles from NANC (non-NA-non-Ach) nerves?

Answer 4

Nitric oxide (NO)

Question 5

What hormone can be released from post-ganglionic autonomic nerves onto smooth cells from the adrenal medulla?

Answer 5

Adrenaline

Question 6

How is smooth muscle contraction initiated?

Answer 6

By an increase in cytosolic Ca2+

Question 7

How is there an increase in cytosolic Ca2+ ?

Answer 7

• By influx from extracellular medium
• Release of Ca2+ from internal Ca2+ stores (from sarcoplasmic reticulum

Question 8

What is calmodulin (CaM)?

Answer 8

A Ca binding protein

Question 9

How does smooth muscle use a Ca2+- Calmodulin complex to generate a muscle contraction?

Answer 9

• Ca2+ binds to to calmodulin
• This Ca2+ and calmodulin complex activates the myosin light chain kinase (MLCK)
• MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity
• Actin myosin crossbridges slide along actin, creating muscle tension

Question 10

In the absence of a rise in cytosolic Ca2+, what compound produces relaxation and how?

Answer 10

• Myosin light chain phosphatase
• Due to the myosin light chain being dephosphorylated, MLCP activity becomes dominant, leading to relaxation

Question 11

How can cytosolic Ca2+ decrease?

Answer 11

• Ca2+ can be untaken into the SR- via Ca2+ ATPase
• Extrusion of Ca2+ from cell via Ca2+ ATPase and Na-Ca exchanger (1Ca+ moves out, 3Na+ move in)

Question 12

How does stimulation of Gq mediated receptors produce a rise in intracellular Ca from voltage gated calcium channels?

Answer 12

• When a neurotransmitter binds to Gq protein receptors, it stimulates Na channels (ion channels) to open, causing depolarisation of the cell
• This creates an excitatory junctional depolarising potential, which, if reaches the threshold value of -40mV, activates the opening of VGCC
• This causes an influx of Ca2+

Question 13

How does stimulation of Gq protein receptors cause the release of Ca2+ from internal Ca2+ stores in smooth muscle?

Answer 13

• Stimulation of Gq receptors causes Pip2 to be converted into IP3 and DAG via PLC.
• IP3 binds to IP3 receptors (these are ligand gated receptors) on the sarcoplasmic reticulum, which opens the ion channel, leading to an influx of Ca2+ down a concentration gradient, due to there being low Ca2+ in cytosol, and high in the SR