CHAPTER 3 • CELLULAR STRUCTURE AND FUNCTION
57
8.
A patient with a complaint of leg pain
is found to have a blood clot in a large
artery in his leg; he is subsequently
diagnosed with peripheral artery disease.
Because peripheral artery disease is
associated with endothelial dysfunction,
which of the following could have con-
tributed to the formation of the blood
clot?
a. Increased endothelial production of
nitric oxide and prostacyclin.
b. Diminished endothelial production of
cGMP.
c. Increased endothelial production of
prostacyclin and decreased produc-
tion of endothelin-1.
d. Decreased endothelial production of
nitric oxide.
ANSWERS TO REVIEW QUESTIONS
1.
The correct answer is “b” because
myosin light chain kinase is involved in
myosin phosphorylation in both types of
muscle. Choice “a” is incorrect because
dense bodies are specialized regions
found only within vascular smooth mus-
cle cells where bands of actin filaments
are joined together. Choices “c” and “d”
are incorrect because these structures
are found in cardiac muscle cells, not
smooth muscle cells.
2.
The correct answer is “b” because
myosin is the major component of the
thick filament. Choices “a,” “c,” and
“d” are incorrect because they are all
components of the thin filament.
3.
The correct answer is “c” because a
myosin-binding site is exposed on the
actin after calcium binds to TN-C.
Choices “a” and “b” are incorrect
because calcium binds to TN-C, not
myosin or TN-I. Choice “d” is incorrect
because SERCA pumps calcium back
into the sarcoplasmic reticulum.
4.
The correct answer is “d” because
phosphorylation of the L-type calcium
channels by protein kinase A increases
the permeability of the channel to cal-
cium, thereby permitting more calcium
to enter the cell during depolarization,
which triggers the release of calcium
by the sarcoplasmic reticulum. Choice
“a” is incorrect because Gi-protein
activation decreases cAMP formation,
thereby decreasing inotropy. Choice “b”
is incorrect because calcium binding to
TN-C enhances inotropy. Choice “c” is
incorrect because it is the calcium that
is released by the terminal cisternae of
the sarcoplasmic reticulum that binds to
TN-C leading to contraction.
5.
The correct answer is “a” because myo-
sin light chain kinase activation by cal-
cium-calmodulin phosphorylâtes myosin
light chains, which induces contraction.
Choices “b” and “d” are incorrect because
myosin light chain phosphatase activa-
tion dephosphorylates the myosin light
chains, which causes relaxation. Choice
“c” is incorrect because there is no tropo-
nin C in vascular smooth muscle.
6.
The correct answer is “c” because angio-
tensin II receptors (AT3) are coupled to
the Gq-protein and activates phospholi-
pase C, which increases IPy Choice “a”
is incorrect because angiotensin II acti-
vates the Gq-protein, not the Gs-protein.
Choice “b” is incorrect because the
Gq-protein stimulates IP3 formation, not
cAMP. Choice “d” is incorrect because
the increase in IP3 stimulates calcium
release from the sarcoplasmic reticulum.
7.
The correct answer is “b” because car-
diac P-adrenoceptors are coupled to
the Gs-protein and cAMP formation,
and the vascular a i -adrenoceptors are
coupled to the Gq-protein and IP3 for-
mation. Choice “a” is incorrect because
cGMP is increased by nitric oxide in
blood vessels, not by Gq-protein activa-
tion. Choice “c” is incorrect because
vascular a i -adrenoceptors are not
coupled to the Gs-protein. Choice “d”
is incorrect because vascular cAMP is
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