(Stroke. 1998;29:2149-2154.)
© 1998 American Heart Association, Inc.
Myosin Light Chain Phosphorylation and Contractile Proteins in a Canine Two-Hemorrhage Model of Subarachnoid Hemorrhage
Hong Sun, MD;
Kenji Kanamaru, MD;
Masaaki Ito, MD;
Hidenori Suzuki, MD;
Tadashi Kojima, MD;
Shiro Waga, MD;
Yasuko Kureishi, MD;
Takeshi Nakano, MD
From the Department of Neurosurgery (H.Sun, K.K., H.Suzuki, T.K., S.W.)
and First Department of Internal Medicine (M.I., Y.K., T.N.), Mie University
School of Medicine, Mie, Japan.
 |
Abstract
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Background and
Purpose—Subarachnoid hemorrhage (SAH) impairs
both contraction and relaxation response in cerebral arteries. We
tested the hypothesis that cerebral vasospasm might be ATP-independent
contraction, such as latch state, and protein synthesis might be
substantially downregulated due to ATP consumption after
long-lasting contraction.
Methods—Chronic cerebral vasospasm was induced in the
canine 2-hemorrhage model of SAH. The normal and spastic
basilar arteries were stabilized in Krebs-Henseleit solution, and
contraction was induced by 30 µmol/L prostaglandin
F2
(PGF2) in vitro and in vivo. Before
and at 15 minutes and 1 hour after the treatment with
PGF2, the levels of phosphorylated
20-kDa myosin light chain (MLC20) were measured. The time
course of expression of contraction proteins actin and
MLC20, and contraction-inhibiting proteins
h-caldesmon and calponin was determined by
immunoblotting techniques.
Results—A significant vasospasm occurred in the basilar artery
during days 4 to 21, most prominently on days 7 and 14. There were no
significant differences in the baseline levels of
phosphorylated MLC20 between normal and
spastic basilar arteries. The increase in MLC20
phosphorylation by PGF2 was
significantly attenuated in the spastic basilar artery in vitro and in
vivo (P<0.05). The immunoreactivity for actin,
h-caldesmon, and calponin in the spastic basilar
arteries was progressively decreased until day 14 and returned to the
normal level on day 21. In contrast, protein levels of
MLC20 did not significantly change during days 0 to 21.
Conclusions—Chronic cerebral vasospasm closely resembles the
latch state, and temporary deficiencies of contractile proteins may
result from increased destruction and inhibition of protein synthesis.
Key Words: cerebral ischemia, transient • myosin light chain • phosphorylation • protein synthesis • dogs
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Introduction
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Delayed cerebral vasospasm following subarachnoid
hemorrhage (SAH) has been generally attributed to sustained
tonic contraction.1 2 3 4 Intracellular
Ca2+ increases in smooth muscle cells during
cerebral vasospasm,5 6 7 8 and this increase in
Ca2+ also activates
calmodulin and myosin light chain kinase
(MLCK).9 10 11 Phosphorylation of
20-kDa myosin light chain (MLC20) by MLCK is
considered to be the first step in vascular
contraction.9 10 11 Although
MLC20 phosphorylation is observed
in the acute phase of contraction, it does not last a long
time.9 10 11 In addition, a progressive decrease in
the ATP level is observed concomitant with the development of
vasospasm.12 13 14 In the absence of ATP, the
crossbridges formed by the N-terminal (catalytic) head of
myosin are attached to actin filaments, forming the characteristic
rigor pattern.9 10 The mechanism of this
high-force, low-phosphorylation, and
low-energy-consumption state, named "latch," is not known; in a
2-state contractile model, it results from an increase in the ratio of
crossbridge attachment/detachment constant.10
Dephosphorylation, although necessary for
the initiation of relaxation, is not its only rate-limiting step
under all conditions, as it can be significantly faster than
relaxation.10 Any contribution to latch by the
thin-filament-associated proteins
h-caldesmon15 and
calponin16 must be auxiliary, because smooth
muscle can be fully relaxed by dephosphorylating
MLC20.10 However, time
courses of MLC20 phosphorylation
and of protein levels have not been demonstrated in the same model of
SAH. Therefore, the purpose of our study was twofold: first, to
investigate the time course of MLC20
phosphorylation after SAH; and second, to measure the
expression of the contraction proteins actin and myosin and the
contraction-inhibiting proteins h-caldesmon and calponin.
This was an observational study to determine the state of myosin
phosphorylation in vasospasm and the state of
contractile proteins.
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Materials and Methods
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The animals were cared for in accordance with the Guidelines for
Animal Experiments in the Mie University School of Medicine.
Seventy-eight adult mongrel dogs of both sexes, weighing 12 to 16 kg,
were randomly assigned to 2 groups, with 23 in the normal control group
and 55 in the SAH group.
On day 0, each dog in the SAH group was anesthetized by
intramuscular injection of ketamine hydrochloride (10 mg/kg)
and intravenous injection of pentobarbital sodium (15
mg/kg). The animals were intubated, and a peripheral venous
line was placed. An intravenous injection of pentobarbital
sodium (20 mg/kg per hour) maintained anesthesia, and
pancuronium bromide (0.05 mg/kg per hour) maintained paralysis. A 2:1
mixture of N2O and O2 on a
ventilator (SN-480–3, Shimano Co) was used to maintain the
end-tidal CO2 (ETCO2) level
at approximately 40 mm Hg during continuous
ETCO2 monitoring (POET 601, Criticare System,
Inc). Body temperature was maintained at 37°C with a heating blanket,
and the mean arterial blood pressure and pulse rate of the
femoral artery were continuously monitored. Vertebral angiography was
carried out via the catheter through the femoral artery. During
angiography, exposure factors were maintained constant, and a
radiopaque control standard was used for correction to constant
magnification. SAH was induced by injections of 0.5 mL/kg fresh
autologous arterial blood into the cisterna magna 48 hours
apart. Vertebral angiography was repeated on days 4, 7, 14, and 21
after the first injection of blood. The caliber of the basilar artery
was measured on the angiograms at 3 locations: close to the
vertebrobasilar junction, at the midpoint, and close to the basilar
tip. The changes in the diameters were expressed as percentages of the
baseline value before SAH.
Tissue Preparation for Measurement of MLC20
Phosphorylation
After the second angiography, the basilar artery from vertebral
union to basilar bifurcation was excised via the transclival approach
on days 4 (n=5), 7 (n=11), 14 (n=3), and 21 (n=3). Eleven normal
basilar arteries were also removed by the same surgical procedures. In
the SAH group, after the blood clot around the basilar artery and its
branches were carefully removed, the basilar artery was immersed in
Krebs-Henseleit solution (KHS, mmol/L: NaCl 115.0, KCl 4.7,
CaCl2 2.5, MgCl2 1.2,
NaHCO3 25.0,
KH2PO4 1.2, and
D-glucose 10.0). The basilar arteries were incubated in a
bath containing KHS aerated with 5% CO2 and 95%
O2 at 37°C for 1 hour. The in vitro basal
phosphorylation levels of MLC20
were determined in the spastic basilar arteries from day 7 animals
after SAH (n=5). To test the additional phosphorylation
of MLC20 by agonist, other spastic basilar
arteries from day 7 animals (n=6) and normal basilar arteries (n=6)
were further treated with 30 µmol/L
PGF2 for 15 minutes or 1 hour. At the end of
incubation, the arterial segments were frozen in liquid
nitrogen and stored for biochemical examinations.
After the second angiography, the basilar arteries were exposed via the
transclival route on days 4 (n=3), 7(n=9), and 14 (n=3). The blood
clots around the basilar artery were carefully removed, and the cranial
window was superfused with KHS aerated with 5%
CO2 and 95% O2 at 37°C
for 1 hour. The in vivo basal phosphorylation levels of
MLC20 were determined in the spastic basilar
arteries on day 7 (n=3). As with the in vitro study, the exposed
spastic basilar arteries on day 7 (n=6) and normal basilar arteries
(n=6) were further treated with 30 µmol/L
PGF2 for 15 minutes or 1 hour. During the
treatment, ETCO2 was adjusted to 40 mm Hg.
For the determination of phosphorylation levels of
MLC20, liquid nitrogen and frozen acetone
containing 10% TCA and 10 mmol/L DTT were directly added
into the cranial window, and the frozen basilar arteries were quickly
excised.
Tissue Preparation for Measurements of Contractile
Proteins
The dogs were killed by exsanguination and infusion of saline
into the left ventricle on days 4 (n=6), 7 (n=6), 14 (n=3), or 21 (n=3)
after the initial SAH. The brain was removed, and the blood clots
around the basilar artery were carefully removed. The basilar artery
was quickly frozen in liquid nitrogen and stored for biochemical
examination.
Measurements of MLC20 Phosphorylation
The extent of MLC20
phosphorylation was measured through separation of
phosphorylated and nonphosphorylated
forms by urea-glycerol gel electrophoresis followed by electrophoretic
transfer of the proteins to a nitrocellulose membrane. The relative
amount of each form was quantified by an immunoblot
procedure described in the next section. The arterial
segments were frozen by immersion in acetone containing 10% TCA and
10 mmol/L DTT cooled with liquid nitrogen. The frozen tissues were
washed twice with acetone containing 10 mmol/L DTT to remove the
TCA and then dried, weighed, and cut into small pieces. The pieces were
homogenized for 2 minutes at 4°C in 10 µL urea
buffer/mg sample containing 8 mol/L urea, 10 mmol/L DTT, 18
mmol/L Tris base, 20 mmol/L glycine, 250 mmol/L sucrose, and
0.004% bromophenol blue with use of a Potter Teflon
homogenizer. These urea-solubilized samples (20 µL)
were subjected to urea-glycerol gel electrophoresis and
immunoblot analysis, using the specific
MLC20 antibody as
documented.17 18 Anti-MLC20
rabbit polyclonal antibodies were provided by Dr J.T. Stull (University
of Texas Southwestern Medical Center, Dallas, Tex). The region
containing MLC20 was visualized as dark blue
bands, using 4-chloro-1-naphthol. The extent of
MLC20 phosphorylation was
calculated by dividing the area of phosphorylated
MLC20 by the total area of both
phosphorylated and nonphosphorylated
MLC20.
Measurements of Contractile Proteins
The unfixed basilar arteries were weighed, cut into small
pieces, and homogenized for 2 minutes at 4°C in 10 µL
buffer/mg sample containing 30 mmol/L Tris-HCl (pH 7.0), 500
mmol/L NaCl, 5 mmol/L ATP, 2 mmol/L EGTA, 4 mmol/L EDTA,
1 µmol/L DTT, 10 µg/mL leupeptin, 1 mmol/L benzamidine,
and 10 µmol/L -PMSF with a Potter Teflon
homogenizer. Proteins in the homogenate
were separated with SDS-PAGE, followed by electrophoretic transfer of
the proteins to a nitrocellulose membrane. The protein concentrations
were determined with the Bradford (Bio-Rad) procedure with bovine serum
albumin as a standard. The membrane was processed for
immunoblotting analysis with the specific
antibodies of actin, h-caldesmon, calponin, and
MLC20 and developed by the enhanced
chemiluminescence method (Amersham). Since 2 smooth muscle–specific
actin isoforms designated as - and 
-SM and 2 nonmuscle actin
isoforms (ß- and -NM) are expressed in vascular smooth muscle
cells,19 we used anti-actin antibody to all actin
isoforms (Sigma). Anti-h-caldesmon and anti-calponin
polyclonal antibodies were provided by Dr M.P. Walsh (University of
Calgary, Calgary, Alberta, Canada). Quantification of each specific
band was performed by densitometry (Densitograph, Atte Japan), and the
quantity after SAH was expressed as the percentage of that in the
normal basilar artery.
Statistical Analysis
All values are given as mean±SD. Statistical comparison was
made by the Student t test and intergroup comparisons by
ANOVA. The level of significance of all tests of comparison was
P<0.05.
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Results
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Changes in the Basilar Artery Diameters
After the induction of SAH, the angiographic diameters of the
basilar arteries gradually decreased, as shown in Figure 1
. The percentage of the diameters from
baseline values were as follows: day 4, 70.6±11.9%; day 7,
55.2±6.1%; day 14, 51.8±3.7%; and day 21, 66.9±5.6%. The
narrowing of the basilar artery was most prominent on days 7 and 14.
Mild vasospasm was observed on days 4 and 21 to the same degree.
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Figure 1. Percent diameters of the canine basilar artery
after SAH. The diameter of the basilar artery in the control was taken
as 100%. Vertical lines indicate SD. There are significant differences
between the control and the values on days 4 to 21.
*P<0.001 each diameter versus control.
 P<0.05 between days 7 and 4 or 21, and between days
14 and 4 or 21.
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Levels of MLC20 Phosphorylation
The time course of baseline MLC20
phosphorylation is shown in Figure 2. The percentages of
phosphorylated MLC20 in the
spastic basilar arteries in vitro were as follows: day 0 control,
8.2±2.8%; day 4, 9.2±4.1%; day 7, 9.5±2.1%; day 14, 5.4±3.8%;
and day 21, 4.3±5.6%. There were no significant differences in
phosphorylation levels at any stage of measurements,
regardless of vasospasm. The percentages of
phosphorylated MLC20 in the in
vivo spastic basilar arteries were as follows: day 0 control,
55.3±7.5%; day 4, 60.1±9.6%; day 7, 58.7±7.3%; and day 14,
53.8±8.1%. Again, there were no significant changes at any stage of
measurements.
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Figure 2. Levels of MLC20
phosphorylation in the control and spastic basilar
arteries in vitro and in vivo. Vertical bars indicate SD. There are no
significant changes during days 0 to 21. The lower photographs show
immunoblots of nonphosphorylated and
phosphorylated MLC20 in the normal (lane 1)
and spastic basilar arteries removed on day 4 (lane 2), day 7 (lane 3),
day 14 (lane 4), and day 21 (lane 5) after SAH. MLC20
indicates nonphosphorylated MLC20;
MLC20-P, phosphorylated
MLC20.
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MLC20 Phosphorylation After
PGF2 Treatments
After incubation with 30 µmol/L
PGF2 in vitro, the changes of
MLC20 phosphorylation in the
spastic basilar artery and control are shown in Figure 3. In the control artery, the
MLC20 phosphorylation
significantly increased from 8.2±2.8% to 37.7±2.7% at 15 minutes
and 34.4±4.1% at 1 hour. In the spastic basilar arteries, the
MLC20 phosphorylation increased
from 9.5±2.1% to 19.8±2.5% at 15 minutes and 20.1±1.9% at 1 hour.
The levels of MLC20
phosphorylation significantly increased from the
baseline level in spastic basilar arteries at 15 minutes and 1 hour
(P<0.05 by the Student t test). However, the
increases in the phosphorylation levels were
significantly attenuated in the spastic basilar arteries
(P<0.01 by ANOVA).
The MLC20 phosphorylation in vivo
after superfusion with 30 µmol/L PGF2
is shown in Figure 4. In the control
artery, topical application of 30 µmol/L
PGF2 induced a sustained contraction during
superfusion. As the contraction developed, the degree of
MLC20 phosphorylation
significantly increased from 55.3±7.5% to 84.6±6.1% at 15 minutes
(P<0.05 by the Student t test) and not
significantly to 72.3±9.0% at 1 hour. In the spastic artery, there
were no significant changes in MLC20
phosphorylation levels after
PGF2 application. The increases in the
phosphorylation levels were significantly attenuated in
the spastic basilar arteries compared with control values
(P<0.05 by ANOVA).
Changes in the Expression of Contractile Proteins
The immunoblotting for actin,
h-caldesmon, calponin, and MLC20 is
shown in Figure 5. The intensities of the
immunoreactive bands for contractile proteins were decreased during
days 7 to 14 and recovered at day 21 (panel A). The immunoreactive band
for calponin was not detected in 3 of the 6 arteries removed on day 7
and 2 of the 3 arteries removed on day 14. In addition, proteolysis of
h-caldesmon and calponin was observed in the spastic basilar
arteries harvested on days 7 and 14 (panel A). Changes in the
densitometric quantities of immunoreactive bands are shown in panel B.
Although MLC20 decreased during days 7 to 14, it
was not significant (panel B). h-Caldesmon, actin and
calponin were significantly decreased in the spastic basilar arteries
harvested on days 7 and 14 (P<0.05) (panel B). On day 21,
all contractile proteins recovered to the control levels.
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Figure 5. A, Immunoblots of actin (42 kDa),
h-caldesmon (120 kDa), calponin (32 kDa), and
MLC20 (20 kDa) in the normal basilar arteries (lanes 1, 2)
and spastic basilar arteries removed on day 4 (lanes 3, 4), day 7
(lanes 5, 6), day 14 (lanes 7, 8), and day 21 (lanes 9, 10) after SAH.
B, Mean percent contents of actin, h-caldesmon,
calponin, and MLC20 in the spastic basilar arteries. The
mean contents of proteins in the control arteries were taken as 100%.
Vertical bars indicate SD. Significant decreases in actin,
h-caldesmon, and calponin were noted on days 7 and 14.
*P<0.01 versus control.
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Discussion
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The present study demonstrated that the degree of
MLC20 phosphorylation in the
basilar arteries did not exhibit significant changes at any stage of
measurement in vitro and in vivo. Second, the increase in
MLC20 phosphorylation induced by
PGF2 was significantly attenuated in the
spastic basilar arteries. Third, the immunoreactivity for actin,
h-caldesmon, calponin, and MLC20
progressively decreased to day 14 after SAH, then recovered on day
21.
Biochemical studies have demonstrated that there are two
Ca2+-dependent regulatory processes in smooth
muscle contraction, namely, MLC20
phosphorylation and a second unidentified site allowing
stress maintenance with reduced cross-bridge cycling
rates.9 10 11 Phosphorylation of
MLC20 initiated by an increase in intracellular
Ca2+ is correlated with the rate of the
actin-myosin interaction in the acute phase of
contraction.9 10 11 In the force
maintenance phase, intracellular Ca2+ is
decreased, and at the same time the MLC20
phosphorylation declines to a steady intermediate
level.9 10 11 Any contractile force developed may
be maintained by the presence of an attached
phosphorylation-independent noncycling cross-bridge
(latch bridge).9 10 11 A number of studies have
demonstrated that activation of the PKC system may play a role in the
latch bridge, inducing a potent and sustained contraction without
affecting MLC20
phosphorylation.1 2 3 4 Low levels
of MLC20 phosphorylation have
been associated with force
maintenance.9 10 11 The ATP contents showed
little or no significant change during tonic
contractions.9 10 11 One recent study demonstrated
that muscle fibers are commonly observed in 3
states.20 (1) In rigor (ie, rigor mortis, the
state obtained in the absence of ATP), all myosin heads are bound
rigidly with actin in a configuration thought to resemble that found at
the end of the power stroke. (2) In relaxation, in the presence of ATP,
myosin heads are largely detached from actin and may be bound in a
helical array around the thick filament or may be disordered and not
bound to either filament. (3) In active muscle contraction, in the
presence of Ca2+ and ATP the myosin heads are
undergoing a cyclic interaction, with actin producing force. ATP
binding was assumed to be a prerequisite for detachment of
dephosphorylated actomyosin and
relaxation.21 Indeed, the ATP content decreased
in parallel with the progression of
vasospasm.12 13 14
Our results do not agree with the findings that
MLC20 phosphorylation
significantly increased in spastic anterior spinal
arteries.5 MLC20
phosphorylation increased in the early phase, but was
undetectable at the later phase of vasospasm using a femoral artery
model.22 Differences in the experimental models
and animal species as well as the sites of arteries may contribute to
the differences in MLC20
phosphorylation levels between the present study
and other studies.
The present study determined the MLC20
phosphorylation of the basilar artery in vivo and
demonstrated that the mean control values for
MLC20 phosphorylation in vivo
were much higher than the basal values in vitro. Under
physiological conditions, the artery is exposed to
hemodynamic stress and constantly contracts to maintain
vascular resistance and regulate blood flow.23
Phosphorylation of MLC20 may take
place in real time in vivo.
Calpain, a calcium-activated protease, has been reported
to be activated in the spastic basilar
artery.24 25 Recently, protein synthesis has been
impaired in smooth muscle cells of spastic cerebral
arteries.26 In our study, the contractile
proteins all progressively decreased whereas there was not a
significant decrease in MLC20. However, these
proteins returned to the normal levels on day 21. These changes were
consistent with the time course of the angiographic vasospasm.
Although some studies have demonstrated that immunoreactivity for actin
is unchanged at the time of vasospasm,26 27 other
studies have shown a decrease of actin on day 7 of
SAH.28 29 In the present study, actin
significantly decreased on days 7 and 14. Myosin was substantially
decomposed on day 7 in the canine 2-hemorrhage
model29; however, it was unchanged in the monkey
model of SAH.27 Our study demonstrated that
immunoreactivity for myosin decreased through days 4 to 21 but not
significantly. It is likely that varying degrees of protein
degradation may reflect the degree of cell
degeneration.26 29
The immunoreactivity of the contraction-inhibiting proteins
h-caldesmon and calponin were significantly decreased during
days 4 to 14 after SAH.26 Both
h-caldesmon and calponin inhibit actin-myosin interaction
without influencing the phosphorylation state of
myosin.15 16 Phosphorylation of
h-caldesmon or calponin by PKC and
Ca2+-calmodulin–dependent kinase
causes a loss of their ability to relax smooth muscle
cells.15 16 In the present study,
immunoblots showed that bands of h-caldesmon and
calponin were significantly decreased on days 7 and 14. Interestingly,
the decreases in h-caldesmon and calponin recovered on day
21, at the resolutional stage of vasospasm. Taken together with the
decrease in actin levels, temporary deficiencies of
h-caldesmon and calponin may result from the increase in
destruction and inhibition of protein synthetic activity.
In conclusion, chronic cerebral vasospasm closely resembles the latch
state, an ATP-independent contraction.
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Acknowledgments
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This work was supported by grants-in-aid for scientific research
(C) and (B) from the Ministry of Education, Science, Sports and
Culture, and a grant-in-aid (1996–1997) from the Mie Medical Research
Foundation (Dr Kanamaru).We thank Dr J.T. Stull for providing the
anti-myosin light chain antibody and Dr M.P. Walsh for providing the
h-caldesmon and calponin antibodies.
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Footnotes
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Reprint requests to Kenji Kanamaru, MD, Department of Neurosurgery, Mie University School of Medicine, Tsu, Mie 514-8507, Japan.
Received May 19, 1998;
revision received June 26, 1998;
accepted June 29, 1998.
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Editorial Comment
R. Loch Macdonald, MD, PhD, Guest Editor
Section
of Neurosurgery University of Chicago Medical Center
Chicago, Illinois
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Introduction
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|---|
Sun et al test the hypothesis that vasospasm is an ATP-independent
contraction like the latch state. The latch state is one theoretical
mechanism that has been postulated to underlie the tonic phase of
smooth muscle contraction. Second, they suggest that protein synthesis
may be downregulated because of ATP consumption after long-lasting
contraction. They found that there was no difference between normal and
vasospastic arteries 4 to 21 days after subarachnoid
hemorrhage in the basal levels of myosin light chain (MLC)
phosphorylation. When contracted with
PGF2, however, vasospastic arteries 7 days
after subarachnoid hemorrhage showed a smaller increase
in MLC phosphorylation in vitro. Second, a
semiquantitative assay showed that there was less actin, caldesmon, and
calponin in vasospastic arteries 7 and 14 days after hemorrhage
compared with control arteries. These findings do not specifically test
and therefore do not directly support or refute their hypotheses.
The double-hemorrhage dog model of vasospasm is widely used.
The vasospasm that occurs is reliable and severe, but it differs from
that observed in humans. Two blood injections are required, and the
vasospasm was still significant 21 days after the first injection.
Vasospasm usually resolves within 14 days of subarachnoid
hemorrhage in humans. Why the vasospasm lasts longer in dogs is
unknown. It is interesting that the decreases in actin, caldesmon, and
calponin occurred 7 and 14 days after hemorrhage and then
recovered by day 21, despite the persistence of angiographic
arterial narrowing. Thus, there is not really a good
correlation between the changes in contractile proteins and vasospasm.
The authors suggest that there is a decrease in protein synthesis
during vasospasm and that this results from a decrease in ATP.
Others1 have shown a decrease in ATP in
vasospastic arteries, but this was not confirmed in the present
experiments. Furthermore, the decrease in protein levels may be caused
by proteolysis rather than decreased protein synthesis.
The authors also report that MLC phosphorylation levels
in vasospastic arteries are the same as in control arteries tested
under the same conditions. This is in keeping with prior studies which
have shown that acute smooth muscle contraction is associated with an
increase in MLC phosphorylation; when, however, the
muscle remains tonically contracted, the level of MLC
phosphorylation falls to near-basal levels. The authors
discuss several postulated mechanisms, including latch state, rigor, or
the action of some other smooth muscle contractile regulatory process.
Their results do not determine which mechanism(s) is active in
vasospasm. They suggest that vasospasm resembles a latch state,
although the data do not rule out other mechanisms, and the latch state
is usually not associated with proteolysis.
In summary, the authors have documented several biochemical alterations
in vasospastic arteries. The cause and importance of the changes remain
to be determined. It is probably only with further detailed
measurements of the changes in the known components of the contractile
apparatus before, during, and after vasospasm that the
mechanisms of vasospasm will be defined.
Received May 19, 1998;
revision received June 26, 1998;
accepted June 29, 1998.
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References
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1.
Kim P, Jones JD, Sundt TM Jr. High-energy
phosphate levels in the cerebral artery during chronic vasospasm after
subarachnoid hemorrhage. J
Neurosurg.. 1992;76:991–996.[Medline]
[Order article via Infotrieve]
Top
Abstract
Introduction
P<0.05 between two groups (Student t
test). The lower photographs show immunoblots of
MLC20 in the normal and spastic basilar arteries before and
after incubation with PGF2