Phys - Smooth Muscle Flashcards by Tiffany Reid

What is missing in smooth muscle?

Sarcomeres
T-tubules or terminal cisternae

SR is poorly developed
-still functions, but extracellular Ca++ is needed

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Caldesmon and Calponin

Actin binding proteins that are modulatory of ATPase

Probably not primary control proteins

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Unlike skeletal muscle, smooth muscle does not have which troponin unit?

Troponin I

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Classification of smooth muscle units

Single unit (visceral or unitary)

Multi unit

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Single unit smooth muscle characteristics

Behaves in a syncytial manner
-All the cels of the single unit act together

Tends to have many gap junctions

Relatively sparse innervation

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Organs with single unit smooth muscles

Small intestine
Colon
Bladder
Uterus 
Ureters

Lymph vessels
Precapillary sphincters

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Do single unit smooth muscles have fast or slow wave potentials?

Slow

Sometimes cause contractions, sometimes do not

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Action potentials of single unit smooth muscles

Spikes

All or none
Almost always contraction
More spikes = stronger contraction

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Slow stretch vs fast stretch of single unit smooth muscle

Slow = lengthening

ex: bladder capacity w/o pressure increase
plasticity or stress relaxation

Fast = contraction
-ex: smallest arterioles or precapillary sphincters

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Organs with multi unit smooth muscle

Ciliary muscle
Iris
Tracheal muscle
Bronchial muscle
GI sphincter
Vas deferens

Resistance vessels
Larger arterioles

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Multi unit smooth muscle characteristics

Each cell acts independently (like skeletal muscle)

Less gap junctions

Higher innervation ratios than single unit

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True or false: multi unit smooth muscle does not have action potentials.

True

Typically

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High progesterone effect of smooth muscle

Reduce gap junctions in myometrial smooth muscle during pregnancy

causes myometrium to behave more like non-innervated multiunit smooth muscle
myometrial muscle remains relatively inactive/dormant/quiescent

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Effects of rising estrogen levels on smooth muscle

Hypertrophy

Increase gap junctions

Myometrial behaves more like a single unit
-parturition

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Morning sickness is caused by__

Reduced number of gap junctions by high levels of progesterone

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High levels of cAMP cause __

Relaxation

by lowering MLCK concentration

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In smooth muscle latch state:
Efficiency is ___
Economy is ___

Efficiency is low
ATP required for control and cross bridge cycling

Economy is high
Absence of shortening
Maintain tone with minimal use of ATP

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Na+ / Ca++ exchanger

3 Na+ / Ca++

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Phospholamban inhibits __

Ca++ ATPase

Phosphorylation of PLB relaxes

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Testing membrane potential of smooth muscle

-55 mV

Due to high Na+ leak

Inward Ca++ current

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Smooth muscle has (a lot of, or few) voltage-gated Na+ channels?

Few

fast channels

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L-type Ca++ channels

Long acting
Slow

Depolarization: ⬆️ intracellular Ca++

Hyperpolarization: ⬇️ intracellular Ca++

Can be blocked by Ca++ channel blockers

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T-type Ca++ channels

Fast

Not blocked by Ca++ channel blockers

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How is smooth muscle unique in activation?

Neurotransmitters, hormones, and drugs can lead to contraction and relaxation

cAMP causes PKA-dependent phosphorylation of ___ which causes __

Phospholamban Increased Ca++ reuptake at the SR RELAXATION

NO and ANP are part of

cGMP-dependent relaxation Decreased myosin light chain phosphorylation

IP3 actions

Releases intracellular Ca++ stores

PLC-dependent contraction is mediated by __

Gq (m1,3,5 and alpha 1 adrenergic)

DAG activates __

PKC Phosphorylates myosin light chains? L-type Ca++ channel phosphorylation

ATP sensitive K channels When are the closed? Open? Mechanism?

Closed when [ATP]i is normal Opens in ischemia (⬇️ ATP) - K+ influx = hyperpolarization - voltage sensitive Ca++ channels close - intracellular Ca++ decreases - smooth muscle relaxes

Ligand operated G protein coupled K channels - mechanism

Agonists : ACh, m2 Adenosine, A1 Activates G alpha 1 type G protein ``` G alpha 1 binds IK(ACh) channel K+ channels open K+ efflux Hyperpolarization L-type Ca++ channels close Relaxation occurs ```

Intermediate filaments of smooth muscle | 2 protein components

Desmin | Vimentin

Dense bodies contain ___ These are functionally analogous to ___ They anchor __

Actinin Z lines Actin

____ allow communication between adjacent smooth muscle cells

Gap junctions and | Mechanical junctions

Smooth muscle contains no __

T tubules Terminal cisternae Sarcomeres Troponin

Actin/myosin ratio in skeletal vs smooth muscle

Skeletal 2:1 | Smooth 10:1

Actin binding proteins whose phosphorylation can affect ATPase and modulate smooth muscle contraction

Caldesmon | Calponin

Light chains serve and essential regulatory function in ___ muscle but not ___ muscle

Smooth | Skeletal

Smooth muscle myosin is thought to be organized in a ___ arrangement whereas skeletal is ___

Side-polar Bipolar *contributes to smooth muscles lack of well defined sarcomeres

What type of smooth muscle is | Small intestine

Single unit/Visceral

What type of smooth muscle is | Uterus

Single unit:Visceral

What type of smooth muscle is Ciliary muscle Iris muscle

Multi unit

What type of smooth muscle is 1. Large blood vessels 2. Small blood vessels 3. Lymph vessels

1. Multi unit | 2-3. Single unit/Visceral

What type of smooth muscle is | Colon

Single unit/visceral

What type of smooth muscle is Urinary bladder Ureters

Single unit/visceral

What type of smooth muscle is Bronchial muscle Trachial muscle

Multi unit

What type of smooth muscle is | GI sphincters

Multi unit

What type of smooth muscle tends to have many gap junctions and sparse innervation?

Single unit/visceral

True or false: | Multi unit smooth muscles do not typically display APs when stimulated to contract

True

Explain "stress relaxation"

Slow stretch of single unit | Bladder stretches and holds urine without increasing pressure

Regulation of smooth muscle contraction occurs on ___ | *skeletal?

Thick filaments Myosin *thin filament

Ca binds ___ and this complex binds ___, and this complex does what?

Calmodulin MLCK -phosphorylates a serine residue on 2 of the light chains

If MLCK is high___

Myosin is largely phosphorylated and has high ATPase activity High Ca levels

Constant and stable low level of contraction. | Seen in what organs?

Tone GI sphincters blood vessels

True or false: | Smooth muscles shorten during the latch state.

False

Efficiency is ___ in smooth muscle | Economy is ___

Low | High

Low levels of ___ cause relaxation in smooth muscle

Phosphorylated myosin light chains

Ca is removed from the cell by ___

Sarcolemma 3 Na/Ca exchanger | Ca ATPase

Resting membrane potential of smooth muscle is

-55