I
N SUMMARY HST 071
U
TERINE PHYSIOLOGY
F
unct
i
onal classification of Cell junctions
O
ccluding junctions
A
nchoring junctions
A
ctin filament attachment sites
C
ell to cell (adhesion belts)
C
ell to matrix (focal contact)
I
ntermediate filament attachment sites
C
ell to cell desmosomes
C
ell
-m
atrix (hemidesmosomes)
C
ommunicating junctions
G
ap junctions
C
hemical synapses
P
lasmodesmata (plants only)
T
he gap junction
• 2
plasma membranes connected by a seres o f structures made up of connexons
• c
onnexon has six subunits
• 2
connexons in register forming
o
pen channels between the two membranes
• C
hannel is 1.5 nm in diameter
• G
ap between membranes is 2
-4
nm
• E
lectrical resistance is determined by number of junctions that are expressed
• R
esistance (measure of gap junction density)
– 1
00 ohm/cm non
-p
regnant
– 5
0 ohm/
c
m at term
• 1
00 ohm/cm for stomach
• 2
50 ohm/cm for taenia caeci
• 4
00 ohm/cm for bladder
• J
unctions increase at time of parturition
• C
onnexin
-4
3 has high turnover rate in labor
• E
stradiol and oxytocin increase levels
• P
rogesterone and hCG decrease levels
S
ignalin
g
in myometrium
• A
ction potentials = electro
-m
echanical coupling
• R
eceptor stimulation = pharmaco
-m
echanical coupling
– H
ormones
• O
xytocin, epinephrine
– C
lassic transmitters
• 5-H
T, acetylcholine
– L
ipid mediators
• p
rostanoids
R
ole of calcium
• G
ood temporal relations
h
ip between intracellular Ca++ and development of force
• C
a++
-c
almodulin activate myosin light chain kinase (MLCK)
• T
his phophorylates a serine residue (Ser 19) in the 20 kDa light chain of myosin (MLC20)
• P
hosphorylated myosin interacts with actin and causes a contraction
• W
hen Ca++ is removed phosphorylation ceases and the muscle relaxes
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