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Bmsc 207 > Muscle IX > Flashcards

Muscle IX Flashcards

1
Q

What are action potentials in smooth muscle initiated by

A

Neural, hormonal, or mechanical stimulation

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2
Q

Where do APs occur in smooth muscle

A

Unitary smooth muscle

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3
Q

What are two types of smooth muscle autonomic AP patterns

A

Some spiky and some plateau
- always have same type
- if spiking always spiking

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4
Q

Why is smooth muscle APs longer

A
  1. Upstroke slower because CA channels propagate AP not Na
  2. Repolarization slower because Ca channels inactivate slowly and there is delayed activation of voltage gated K+ and Ca activated K+ channels
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5
Q

Two types of membrane potentials with spontaneous activity

A

Slow wave potentials and pacemaker potentials

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6
Q

Slow wave potentials

A

Fire APs when reach threshold
- slow depolarization and repolarization with additional input will bring to threshold

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7
Q

Pacemaker potentials

A

Always depolarize to threshold
- continuous firing of APs

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8
Q

What causes contraction in smooth muscle without APs

A

In response to graded depolarizations
- some membrane potential oscillations can lead to tonic contractions in absence of APs

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9
Q

What smooth muscle does not have APs

A

Multi unit smooth muscle
- graded response
- autonomic neurons create local depolarization that spreads in graded fashion throughout muscle fiber triggering Ca entry

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10
Q

What is contraction due to electrical signaling

A

Electromechanical coupling

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11
Q

What are the 3 mechanisms that increase ECF entry and ICF release of Calcium and activate contraction

A
  1. Ca entry through voltage gated channels or ligand gated ion channels
  2. Ca release from SR
  3. Ca entry through voltage independent channels
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12
Q

What are 2 mechanisms of Ca release from SR

A
  • Ca induced Ca release from RyR (have DHP receptors but not mechanically coupled)
  • IP3 Ca release from IP3R
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13
Q

What are the voltage independent channels in smooth muscle

A
  • store operated Ca channels
  • stretch activated channels
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14
Q

What type of voltage gated channels allow Ca entry in smooth muscle

A

Voltage gated L-type Ca channels

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15
Q

How does Ca release from SR in smooth muscle

A

Less SR
- via ca induced ca release and IP3 pathways
- ca enters from L-type channels and bind to RyR to release from SR

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16
Q

What can IP3 pathway cause

A

Contraction and increase in Ca without change in membrane potential or very little

17
Q

What are store-operant channels

A

Depletion of Ca in SR causes activation
Causes Ca influx across membrane
Allows Ca to remain elevated and replenish SR

18
Q

What is pharmomechanical coupling

A

Ca release from SR via IP3 and entry of CA via store operant channels are voltage independent
Occurs when chemical signals change muscle tension with little or no change in membrane potential

19
Q

What can induce smooth muscle contraction independent of AP generation

A

Drugs, excitatory neurotransmitters and hormones

20
Q

How does stretch activated contraction work

A

Stretch causes internal release of Ca from SR through RyR
Stretch shown to cause phosphorylation of myosin light chain leading to contraction

21
Q

What is Ca signal in smooth muscle

A

Ca initiates slow chain of events increasing myosin ATPase activity
- turns on myosin head

22
Q

How is myosin ATPase activated in smooth muscle

A

Low activity at rest
Requires phosphorylation of regulatory light chain to turn on myosin ATPase to hydrolyze ATP

23
Q

How is myosin ATPase activity increased in smooth muscle

A

4 Ca ions bind to calmodulin
When Ca concentration increases calmodulin binds to Ca
When decreases calmodulin releases Ca

24
Q

What is calmodulin

A

Calcium binding protein similar to troponin C of striated muscle

25
Q

Initiation of cross bridge cycling in smooth muscle when Ca bound to calmodulin

A
  1. Ca-calmodulin complex activated myosin light chain kinase
  2. MLCK phosphorylation regulatory light chain near myosin head
  3. Alter conformation of myosin head, increasing ATPase activity and allowed it to interact with actin
26
Q

The smooth muscle cross bridge cycle primarily activates what

A

thick filaments

27
Q

What does increased Ca entering during graded contractions cause

A

More calmodulin acitvated
Increased MLCK activated
More myosin heads activated
Increased force generated

28
Q

What is difference between cross bridge cycling in smooth and cardiac/skeletal muscle

A

Occurs more slowly in smooth
- hydrolysis and release of ADP slower
- shortening and tension occurs over several seconds

29
Q

Cross bridge cycling similar in all muscle types what is difference in smooth

A

Regulatory light chain must be phosphorylated

30
Q

What causes relaxation in smooth

A

1.Ca moved back to SR and extracellular space
2. Regulatory light chain but also be dephosphorylated by myosin light chain phosphatase
3. Some muscle can maintain force after dephosphorylation for extended period of time with little ATP (latch state)

31
Q

What does myosin light chain phosphatase do

A

Removes phosphate groups on regulatory light chain leading to relaxation

32
Q

What is latch state

A

Unknown process
- why smooth can maintain contraction with very little ATP and fatigue
- myosin already bound to actin when dephosphorylation occurs

33
Q

What is force of contraction a balance of

A

Kinase phosphorylation regulatory light chain vs phosphatase dephosphorylating

34
Q

What can alter smooth muscle Ca sensitivity

A

Neurotransmitters, hormones, and paracrine molecules by modulating myosin light chain phosphatase

35
Q

How do you generate more force in smooth

A

Low phosphatase activity sensitized myosin
- inhibiting MLCP or activating MLCK leading to greater contraction at lower Ca

Bmsc 207 (35 decks)

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