4b. Smooth Muscle Flashcards
Smooth muscle
autonomic nervous system
smooth muscle located
vasculature
airways
gut
blood vessel outside
smooth muscle
blood vessel inside
endothelial cells
multi-unit
each cell is innervated separately
so each behaves independently
not coordinated
single-unit
innervated in series
gap junctions permit coordinated contraction
spontaneous action potential
single unit smooth muscles
walls of hollow organs
airways
uterus
visceral smooth muscle
multi-unit smooth muscles
airways
larger arteries
ciliary muscle of eye
smooth muscle structure
smaller than skeletal
single nucleated
no striations
actin and myosin
smooth muscle contraction speed
slower
duration longer
3 types of muscle cells
skeletal - voluntary
cardiac - involuntary
smooth - involuntary
smooth muscle membrane potential
-50 to -60 mV
smooth muscle depolarization rising phase
VG Ca++ channels
+ some Leak Ca++ channels
some smooth muscle can contract w/graded potential
Ca++ pathways into cell in smooth muscle contraction
- VG Ca++ channel
- stretch-activated Ca++ channel
- NT/hormones Gprotein complex
- CICR
- SOCE
How does the G-protein complex induce Ca++ release into Cytosol?
G protein complex stimulates Phospholipase C to release IP3
IP3 binds to SR Ca++ channels
Ca++ released from SR into cytosol
how does CICR release Ca++ into cytosol?
Ca++ from cytosol binds to the CICR
CIRC pumped from SR to cytosol
(positive feedback)
how does Store operated calcium entry (SOCE) work?
SR Ca++ stores become depleted
signal triggers SO Ca++ channel to open
Ca++ flows into Cytosol
smooth muscle contraction
- increase intracellular Ca++
- Ca++ binds to calmodulin (CaM)
- Ca++/CaM activates Myosin Light Chain Kinase (MLCK)
- MLCK phosphorylates light chain in myosin heads (incr ATPase activity)
- cross bridge cycling creates muscle tension
what inhibits MLCK?
cAMP
conformation change
1) increases ATP activity
2) allows myosin/actin interaction
increase cAMP
inhibits MLCK
muscles cannot contract
smooth muscle relaxation
decrease intracellular Ca++
increase MLCP activity
MLCP
myosin light chain phosphatase
how do you activate MLCP?
cGMP
Nitric Oxide (NO)
released by endothelium
causes smooth muscle relaxation
vasodilator
first signs of vascular disease
decrease in NO
how does NO cause smooth muscle relaxation?
NO released by endothelium
NO stimulates guanylyl cyclase
GTP convert to cGMP
increased cGMP causes relaxation of smooth muscles
cGMP
inhibits Ca++ entry
activates MLCP
adrenergic receptors
alpha 1
alpha 2
beta 1
beta 2
cholinergic receptors
muscarinic : M1-M5
nicotinic: N1-N2
blood vessels receptors
most blood vessels have only adrenergic receptors
some have bothh cholinergic and adrenergic
adrenergic receptors cause
mostly vasoconstrictions
some vasodilations
cholinergic receptors cause
only vasodilations
vascular smooth muscle (BV)
alpha 1
NE binds to alpha 1
G-protein complex
Phospholipase C produces IP3
IP3 binds to Ca++
Ca++ released into cytosol
increase Ca++
smooth muscle contraction
(vasoconstriction)
vascular smooth muscle (BV)
beta 2
NE or Epi binds to Beta 2
increase cAMP
inhibits MLCK
smooth muscle contraction
(Vasodilation)
B2 receptors in BV location
BV that support organ/tissue:
coronary
skeletal muscle
pulmonary
BV mainly innervated by
sympathetic nerves
some BV innervated by
parasympathetic nerves
Parasympathetic effects on vasculature
Ach releases NO from endothelium
NO is vasodilator
if you have a damaged endothelium
less NO would be released?
Sympathetic effects on smooth muscles in bornchioles
Epi>NE
NE or Epi binds to beta 2
cAMP increased
inhibits intracellular Ca++ release
decrease Ca++
decrease smooth muscle contraction
(bronchodilation)
parasympathetic effects on smooth muscles in bronchioles
Ach binds to muscarinic receptor
G protein complex
phospholipase C releases IP3
increases cytosol Ca++
increase smooth muscle contraction
(bronchoconstriction)
bronchodilation receptor
Beta 2
bronchoconstriction receptor
M3
Paracrine factors in smooth muscle vasodilation
High CO2
High H+
NO
paracrine factors in smooth muscle vasoconstriction
Low O2
(hypoxic pulmonary vasoconstriction)
endocrine vasoconstrictors
angiotensin II
endothelin
vasporessin
serotonin
endocrine vasodilators
histamine
Stretch (in gut)…
increases contraction
