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Physl > Muscle 15 > Flashcards

Muscle 15 Flashcards

1
Q

What sources of calcium can activate contraction in smooth muscle?

A

Both intracellular and extracellular

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2
Q

What are the three major pathways that smooth muscle cells use to increase calcium levels?

A
  • Voltage gated channels in response to cell depolarization
  • Voltage independent channels
  • Sarcoplasmic reticulum
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3
Q

How do Voltage dependent channels increase the concentration of calcium in smooth muscle?

A

L-type Calcium channels respond to depolarization of the membrane

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4
Q

How do voltage independent channels increase the calcium concentration in smooth muscle?

A
  • Extracellular ligands trigger influx of Ca2+ through ligand gated channels
  • Store operated Ca2+ channels
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5
Q

What leads to Store-operated calcium channels opening in the smooth muscle cells?

A

Depletion of calcium in the SR

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6
Q

What do Store-operated calcium channels do in smooth muscle?

A

They replenish levels of intracellular calcium levels and calcium levels in the endoplasmic reticulum

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7
Q

What isoform of Ryanodine receptors in smooth muscles?

A

RyR3

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8
Q

Through what method do Ryanodine receptors release calcium in the smooth muscle?

A

Through calcium induced calcium release

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9
Q

What additional pathway causes the release of calcium from the Sarcoplasmic Reticulum in smooth muscle?

A

IP3 pathway

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10
Q

What is IP3 in smooth muscle?

A

An intracellular second messenger activated by a G-protein coupled receptor

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11
Q

What activates IP3 in smooth muscle?

A

The binding of a ligand to a g protein coupled receptor in the membrane of the smooth muscle cell

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12
Q

What does IP3 do in smooth muscle cells?

A

Acts on ligand channels in the membrane of the SR to increase calcium release into the cytoplasm

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13
Q

What is the most important pathway for increasing calcium levels for muscle contraction in smooth muscle?

A

The IP3 pathway

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14
Q

How can smooth muscle contract without an action potential?

A

Through the binding of a ligand in the membrane of a muscle cell

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15
Q

What does the smooth muscle cell have instead of the T-tubule system?

A

Invaginations called caveolae

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16
Q

What are found within the Calveoli in smooth muscle?

A

Voltage gated calcium channels

17
Q

What do the voltage gated calcium channels in smooth muscle open in response to and what do they allow in?

A

The open in response to depolarization of the cell membrane and allow calcium from the extracellular space to enter into the muscle cell

18
Q

What are the two ways calcium can be released from the SR in smooth muscle?

A
  • Calcium induced calcium release

* IP3 activation

19
Q

How does calcium induced calcium release occur in smooth muscle?

A

Calcium that entered through the voltage gated calcium channels in the cell then bind to ryanodine receptors in the SR to cause the release of calcium from the lumen of the SR

20
Q

How does the IP3 pathway in smooth muscle work?

A

A ligand binds to a G-protein coupled receptor in the membrane of the smooth muscle cell. This activates IP3 which binds to calcium channels on the SR to cause the release of calcium from the SR

21
Q

What is the intracellular second messenger in the IP3 pathway of smooth muscle?

A

IP3

22
Q

How do the voltage independent ligand gated channels work in smooth muscle?

A

An extracellular ligand can bind and open the channels allowing calcium to enter the cell

23
Q

What is required to induce relaxation in smooth muscle?

A

The myosin light chain must be dephosphorylated by myosin light chain phosphatase in addition to reducing calcium levels

24
Q

What are the mechanisms of removing calcium from the cytoplasm into the extracellular space in all types of muscle?

A
  • Sodium calcium exchanger NCX

* Surface calcium pump PMCA

25
Q

What is the Mechanism for putting calcium back into the SR in all types of muscle?

A

SERCA

26
Q

What binds calcium in the smooth muscle SR?

A

Calreticulin

27
Q

What does Calreticulin do?

A

Binds calcium in the SR to allow more calcium to enter

28
Q

What does Calsequestrin do?

A

Binds to calcium in the skeletal and cardiac SR to allow more calcium to enter

29
Q

What does the Latch-bridge mechanism allow for in Smooth muscle?

A

High force output at a low rate of hydrolysis of ATP

30
Q

How does the Latch-bridge mechanism work?

A

It allows myosin cross-bridges to remain attached to actin after Calcium conc. falls. The decreased rate of detachment allows a greater number of cross bridges to be maintained resulting in lower ATP hydrolysis

Physl (94 decks)

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