Phys - Smooth Muscle Flashcards
What is missing in smooth muscle?
Sarcomeres
T-tubules or terminal cisternae
SR is poorly developed
-still functions, but extracellular Ca++ is needed
Caldesmon and Calponin
Actin binding proteins that are modulatory of ATPase
Probably not primary control proteins
Unlike skeletal muscle, smooth muscle does not have which troponin unit?
Troponin I
Classification of smooth muscle units
Single unit (visceral or unitary)
Multi unit
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
Organs with single unit smooth muscles
Small intestine Colon Bladder Uterus Ureters
Lymph vessels
Precapillary sphincters
Do single unit smooth muscles have fast or slow wave potentials?
Slow
Sometimes cause contractions, sometimes do not
Action potentials of single unit smooth muscles
Spikes
All or none
Almost always contraction
More spikes = stronger contraction
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
Organs with multi unit smooth muscle
Ciliary muscle Iris Tracheal muscle Bronchial muscle GI sphincter Vas deferens
Resistance vessels
Larger arterioles
Multi unit smooth muscle characteristics
Each cell acts independently (like skeletal muscle)
Less gap junctions
Higher innervation ratios than single unit
True or false: multi unit smooth muscle does not have action potentials.
True
Typically
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
Effects of rising estrogen levels on smooth muscle
Hypertrophy
Increase gap junctions
Myometrial behaves more like a single unit
-parturition
Morning sickness is caused by__
Reduced number of gap junctions by high levels of progesterone
High levels of cAMP cause __
Relaxation
by lowering MLCK concentration
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
Na+ / Ca++ exchanger
3 Na+ / Ca++
Phospholamban inhibits __
Ca++ ATPase
Phosphorylation of PLB relaxes
Testing membrane potential of smooth muscle
-55 mV
Due to high Na+ leak
Inward Ca++ current
Smooth muscle has (a lot of, or few) voltage-gated Na+ channels?
Few
- fast channels
L-type Ca++ channels
Long acting
Slow
Depolarization: ⬆️ intracellular Ca++
Hyperpolarization: ⬇️ intracellular Ca++
Can be blocked by Ca++ channel blockers
T-type Ca++ channels
Fast
Not blocked by Ca++ channel blockers
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
- Large blood vessels
- Small blood vessels
- Lymph vessels
- 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
