Smooth Muscle

Question 1

What are the main ways that smooth muscle get Calcium entry?

Answer 1

1. Voltage gates calcium channels in t tubules from AP
2. Stretch receptors
3. Neurotransmitter/hormonal
4. CICR from sarcoplasmic reticulum
5. SOCE when SR is depleted

Question 2

Main differences between smooth muscle and skeletal muscle?

Answer 2

Smooth Muscle

• Smaller than skeletal
• Single nucleated
• Not organized into tight sarcomeres, so no striations
• Still use actin and myosin
• Contraction speed is slower
• Contraction time is longer

Question 3

Explain the steps in smooth muscle contraction

Answer 3

1. Increase in intracellular calcium
2. Calcium binds to calmodulin
3. Ca/Cam binds with Myosin light chain kinase
4. Phosphorylates myosin light chain
5. Crossbridge cycling occurs

Question 4

Explain steps of smooth muscle relaxation

Answer 4

1. Can change contraction by altering levels of Ca2+ and myosin phosphatase activity
2. For relaxation the cell needs to have low Ca2+ and increased myosin phosphatase activity

Note: Binding of ATP to the myosin heads is slow, can sustain contractions

Question 5

What is the role of endothelium in vascular smooth muscle relaxation?

Answer 5

It releases nitric oxide that causes smooth muscle relaxation
-One of the first signs of vascular disease is a decrease in NO

Question 6

Adrenergic and cholinergic receptors in blood vessels

Answer 6

Question 7

What normal degrades cGMP? What drug inhibits this?

Answer 7

Phosphodiesterases (PDE5)
Viagra inhibits this, leads to more vasodilation

Question 8

What happens when NE binds to alpha 1 receptors on vascular smooth muscle of blood vessels?

Answer 8

1. GPCR pathway is activated
2. Gq -> PLC -> IP3(second messenger) -> increase Ca²⁺
3. Increases myosin and actin interaction
4. Increase contraction of smooth muscle (vasoconstriction)

Question 9

What happens when there are sympathetic effects on smooth muscle around some blood vessels on B2 receptors?

Answer 9

1. GPCR is activated
2. Gs -> Adenylyl cyclase -> ATP is converted to cAMP(second messenger)
3. cAMP inhibits MLCK
4. Decreases actin and myosin interaction
5. Decreases contraction of smooth muscle (vasodilation)

Question 10

What are the parasympathetic effects on vasculature?

Answer 10

First of all there are Ach receptors on the endothelium and smooth muscle

• Ach releases NO from endothelium, once in blood vessels it causes vasodilation
• Ach can also directly cause smooth muscle contraction (IP3)

Question 11

What are the sympathetic effects on B2 receptors in bronchiole smooth muscle?

Answer 11

Epinephrine >> Norepinephrine

1. Gs -> Adenylyl cyclase -> cAMP -> PKA -> closes Ca²⁺ channels
2. Decrease in myosin and actin interaction
3. Decrease in contraction of smooth muscle (bronchodilation)

Question 12

What are the parasympathetic effects on smooth muscle in bronchioles?

Answer 12

1. Ach binds to muscarinic receptors
2. Gq -> PLC -> IP3 (second messenger) -> Increase Ca²⁺
3. Increase in smooth muscle contraction (bronchoconstriction)

Question 13

What are some paracrine/local factors that cause vasodilation of smooth muscle?

Answer 13

High CO2
High H⁺
NO

Question 14

What are some endocrine factors that can affect smooth muscle excitation/relaxation?

Answer 14

• Hormones
• Angiotensin II, endothelin, vasopressin, serotonin, histamine
• Bind to a receptor and open ion channels, etc. that causes depolarization or hyperpolarization
• Self excitation/pacemaker