L4 Smooth Muscle Physio

Question 1

Describe functional characteristics of striated (actin linked) and smooth muscle (myosin linked) EC coupling mechanisms

Answer 1

Striated muscle has troponin on actin filaments

Smooth muscle has no troponin, Ca binds with Calmodulin

Question 2

What are the three types of Ca channels in smooth muscles?

Answer 2

Voltage-gated, ligand-gated and IP3 gated Ca channels

Question 3

Describe difference between electromechanical and pharmomechanical coupling in smooth muscle

Answer 3

???

Question 4

How does alpha-adrenergic stimulation cause smooth muscle activation?

Answer 4

NE and Epi (Symp) bind to a1 receptors and IP3 leads to smooth muscle contraction
-This is the predominant sympathetic response

Question 5

How does beta-adrenergic stimulation cause smooth muscle relaxation?

Answer 5

NE and Epi (Symp) bind to B1 receptors and cAMP leads to smooth muscle relaxation

Question 6

How does NO cause smooth muscle relaxation?

Answer 6

NO is released by endothelial vascular cells in response to ACh
-When no endothelial cells around (= no NO), ACh leads to contraction of smooth muscle

Question 7

Explain interaction between endothelial and smooth muscle cells in response to PS nerve activity in vasculature.

Answer 7

• ACh binds to muscarinic receptor on smooth muscle cell and leads to contraction
• ACh bind to muscarinic receptor on endothelial cell, NO released and relaxation occurs

Question 8

What are the four distinctions of smooth muscle?

Answer 8

Single unit, multi unit, tonic, phasic

Question 9

Describe the mechanism of smooth muscle contractile protein activation

Answer 9

AP
Opening of Ca channels
Increase in Ca
Ca binds to calmodulin (instead of troponin)
Ca-Cal activates myosin light chain kinase (MLCK)
MLCK phosphorylates a myosin light chain
Active myosin binds to actin and cross bridge action occurs

Question 10

What does myosin light chain phosphatase do?

Answer 10

MLCP dephosophrylates myosin bound to actin

This occurs when Ca levels drop and relaxed state occurs

Question 11

What is the latch bridge formation?

Answer 11

In smooth muscle, once activated, you can let Ca levels drop very low and myosin and actin will still loosly interact causing tonic/lax tension
-Found mostly in vascular smooth muscle

Question 12

What is the mechanism for IP3 gated Ca channels in smooth muscle?

Answer 12

Hormone/NT binds to receptor
Phopholipase C is activated
PLC converts PIP2 to IP3
IP3 binds to receptors on Ca channels on SR
Ca release and intracellular Ca increases
-Also get CICR where Ca influx from voltage and ligand gated channels can open Ca channels on SR to release more Ca