© 1997 American Heart Association, Inc.
Articles |
Differential Effects of Extracellular Mg2+ on Thrombin-Induced and Capacitative Ca2+ Entry in Human Coronary Arterial Endothelial Cells
From the First Department of Internal Medicine (M.Y., H.M., T.I., G.K.) and the Department of Clinical Laboratory Medicine (T.O., M.K.), Hiroshima University School of Medicine, Hiroshima, Japan.
Correspondence to Mitsuisa Yoshimura. MD, First Department of Internal Medicine, Hiroshima University School of Medicine, 1-2-3 Kasumi, Minami-ku, Hiroshima 734, Japan. E-mail myoshimu{at}mcai.med.hiroshima-u.ac.jp
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
Abstract Receptor-mediated and capacitative Ca2+ entry are the primary Ca2+ entry pathways in endothelial cells (ECs). The mechanisms for Ca2+ entry via these pathways have not been fully elucidated. In this study, the effect of low and high external Mg2+ concentrations on these Ca2+ entry pathways was examined in human coronary arterial ECs. External Mg2+ concentration did not affect cytosolic free Mg2+ concentration. After exposure to thrombin in Ca2+-free medium, addition of Ca2+ to the medium caused a rise in cytosolic free Ca2+ concentration ([Ca2+]i), indicating thrombin-induced Ca2+ influx. Thrombin-induced Ca2+ influx was inhibited by not only low but also high external Mg2+ concentrations. After depletion of endoplasmic Ca2+ stores by thapsigargin, addition of Ca2+ to the medium induced an increase in [Ca2+]i, indicating capacitative Ca2+ entry. Capacitative entry was found to be accelerated by low external Mg2+ and inhibited by high external Mg2+ concentration. Results suggest that receptor-mediated Ca2+ influx requires external Mg2+ but is inhibited by increased external Mg2+ concentrations and that capacitative Ca2+ entry is reduced by external Mg2+ in human coronary arterial ECs.
Key Words: extracellular magnesium • endothelial cells • calcium entry
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Vascular ECs regulate vasomotor tone by releasing endothelial-derived relaxing factors in response to physical stimuli and vasoactive agonists such as thrombin.1 An important endothelial-derived relaxing factor is NO, which is synthesized by NO synthase.2 The activation of NO synthase is coupled to elevation of [Ca2+]i.3,4 Agonists that induce NO release induce a biphasic increase in [Ca2+]i that is composed of an initial release of Ca2+ from intracellular stores followed by sustained Ca2+ entry through the plasma membrane.5 NO production is not related to the peak [Ca2+]i, but is dependent on the sustained elevation of [Ca2+]i.6
Abnormal Mg2+ status has been reported to be important in the pathogenesis of cardiovascular disease. Magnesium supplementation has a beneficial effect on the vascular disease process.7,8 Therefore, Mg2+ is thought to be an important regulator of the vascular system. The effect of Mg2+ on coronary arteries is thought to be mediated by ECs and vascular smooth muscle cells.
Assessment of the effect of Mg2+ on Ca2+ handling is a very important aspect of the mechanism of Mg2+ action. There is general agreement concerning the inhibitory effect of extracellular Mg2+ on Ca2+ influx via voltage-gated Ca2+ channels in vascular smooth muscle cells.9 However, the existence of voltage-gated Ca2+ channels has been ruled out in ECs.3,10 Little is known about the effect of external Mg2+ on Ca2+ influx in ECs. The present study was designed to assess the effect of external Mg2+ on receptor-mediated Ca2+ influx elicited in human coronary arterial ECs by the potent coronary vasoconstrictor thrombin. Because the filling state of the endoplasmic reticulum with Ca2+ has been reported to regulate Ca2+ influx from the extracellular space in ECs,3,11 the effect of external Mg2+ on Ca2+ influx activated by the depletion of intracellular Ca2+ stores (capacitative Ca2+ entry) was also investigated.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Reagents
Gentamicin, amphotericin B, hydrocortisone, human epidermal growth factor, fetal bovine serum, bovine brain extract, trypsin-EDTA, and modified MCDB 131 medium were obtained from Clonetics. Fura 2-AM, mag-fura 2-AM, and mag-fura 2 tetrapotassium salt were from Molecular Probes. Stock solutions (1 mmol/L) of fura 2-AM and mag-fura 2-AM were prepared in dimethylsulfoxide. All other chemicals were from Sigma Chemical Co.
EC Culture
Human coronary arterial ECs that were
passage 3 were purchased from Clonetics and were cultured in modified
MCDB 131 medium supplemented with 5% fetal bovine serum, 10
ng/mL of human epidermal growth factor, 12 µg/mL of
bovine brain extract, 1 µg/mL of hydrocortisone, 50
µg/mL of gentamicin, and 50 ng/mL of amphotericin B.
The cells were seeded into 100-mm culture dishes and cultured at 37°C
under 95% air and 5% CO2. At confluency, cells
were harvested for passage with a trypsin-EDTA solution (0.025%
trypsin and 0.01% EDTA) and were used after 5 to 7 passages. In the
preliminary study, we compared the effects of external
Mg2+ on Ca2+ influx induced
by thrombin and thapsigargin between passages 3 and 7. However, there
was no significant differences between the two groups. The magnitude of
Ca2+ influx induced by thrombin or thapsigargin
was less in passages after 9 in passages 3 and 7. Therefore, we
performed experiments on cells between passages 5 and 7. For each
experimental protocol, three to five separate culture preparations were
studied.
Measurement of [Ca2+]i
ECs were allowed to attach to glass coverslips. Coverslips were
washed twice with PSS containing 145 mmol/L NaCl, 5
mmol/L KCl, 5 mmol/L glucose, and 10
mmol/L HEPES (pH 7.4), supplemented with 1 mmol/L
CaCl2 and 1 mmol/L
MgSO4. Cells were then incubated for 60 minutes
at 37°C in PSS containing 3 µmol/L fura 2-AM, 1
mmol/L CaCl2, and 1 mmol/L
MgSO4. The coverslips were rinsed twice with the
same medium without fura 2-AM to remove extracellular dye and stored in
the dark at room temperature until use. Immediately before measurement,
the coverslips were inserted into a cuvette containing either 2.5 mL of
Ca2+-containing PSS (PSS plus 1
mmol/L CaCl2) or 2.5 mL of
Ca2+-free PSS (PSS plus 1 mmol/L
EGTA) with nominally 0 or 1 mmol/L
MgSO4. EGTA was added immediately before
insertion of the coverslip into the cuvette. Fluorescence was
monitored at 510 nm (excitation wavelengths of 340 and 380 nm) in a
dual excitation wavelength spectrofluorometer (SPEX Fluorolog; SPEX
Industries) equipped with a thermostatically controlled chamber at
37°C and a stirrer. Data were collected using dM3000 software (SPEX
Industries). Integration time was 0.3 second at each wavelength, and
the time increment was 1.0 second. After a stable basal value was
obtained, cells were exposed to the test agent. Because the cuvette was
not perfused, a new steady state was achieved immediately after the
addition of drugs by stirring. Stirrer speed was kept constant to
exclude the influence of varying flow rate on
[Ca2+]i.12 Each coverslip
was exposed to only one agent. Repetitive determinations were not made.
The [Ca2+]i was estimated by the ratio method
described previously.13 At the end of each
experiment, the cells were incubated with 10 µmol/L
ionomycin in the presence of 1 mmol/L
CaCl2 to obtain the maximum fluorescence
ratio. Subsequent incubation in 5 mmol/L EGTA at pH 8.3
allowed determination of the minimum fluorescent ratio.
Autofluorescence from unloaded cells, test agents, and medium
was subtracted from measured values.
Measurement of [Mg2+]i
ECs on coverslips were loaded with 1.5 µmol/L
mag-fura 2-AM for 30 minutes at 37°C in the same medium used for fura
2-AM loading. All fluorescent measurements were performed in
either Ca2+-containing PSS or
Ca2+-free PSS with four different concentrations
of MgSO4 (nominally 0, 1, 10, or 30
mmol/L). Fluorescence was monitored at 510 nm, with
excitation wavelengths of 340 and 380 nm. The
[Mg2+]i was determined as previously
described14 using an in vitro calibration method.
Mag-fura 2 tetrapotassium salt (100 nmol/L) was dissolved in the
calibration solution (120 mmol/L KCl, 20 mmol/L
NaCl, and 5 mmol/L HEPES) containing either 2
mmol/L CaCl2 plus 1 mmol/L
MgSO4, or 5 mmol/L EDTA plus 8
mmol/L Tris, to generate the maximal and minimal
fluorescence ratios, respectively. In this system, maximal and
minimal fluorescence ratios were 25.75 and 0.62,
respectively.
Determination of Ca2+ Entry
To assess Ca2+ entry through the plasma
membrane, cells were exposed to 25 µL of 100 U/mL of thrombin (final
concentration of 1.0 U/mL) or 25 µL of 0.1 mmol/L
thapsigargin (final concentration of 1 µmol/L) in 2.5 mL
of Ca2+-free PSS containing nominally 0 or 1
mmol/L MgSO4. The
[Ca2+]i reached a peak value, corresponding to
the Ca2+-mobilizing agent-stimulated
Ca2+ discharge or mobilization from intracellular
Ca2+ stores and then returned to baseline.
Subsequently, 50 µL of 100 mmol/L
CaCl2 was added to the medium (final
concentration of 2 mmol/L). The increase in
[Ca2+]i after addition of
Ca2+ to the medium was defined as the
agent-induced Ca2+
entry.9
Statistical Analysis
Data are expressed as mean±SEM. Mann-Whitney U test
was used to compare the [Ca2+]i levels among
the experimental groups. ANOVA with repeated measures was used to
compare the time course of changes in [Mg2+]i
levels. A value of P<.05 was considered statistically
significant.
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Effect of Extracellular Mg2+ on [Mg2+]i
In our experiments to investigate the effect of external Mg2+ on the Ca2+ movement across the plasma membrane, cells were incubated in the solution containing a variety of external Mg2+ concentrations during up to about 20 minutes. It is important whether the change in extracellular Mg2+ is accompanied by the change in [Mg2+]i in the present study. To examine the effect of extracellular Mg2+ on [Mg2+]i, mag-fura 2-loaded cells were incubated for 20 minutes in Ca2+-containing PSS with nominally 0, 1 (standard Mg2+), 10, or 30 mmol/L MgSO4. The time course of the effect of external Mg2+ concentration on [Mg2+]i is shown in Table 1
. [Mg2+]i was
not significantly affected by the external Mg2+
concentration during short-term (20 minutes) incubation. Thrombin (1.0
U/mL) or thapsigargin (1 µmol/L) had no significant
effect on [Mg2+]i in standard
Mg2+ PSS (data not shown). In
Ca2+-free PSS, external
Mg2+ also did not affect
[Mg2+]i (data not shown).
|
Effect of Reduced Levels of Extracellular Mg2+ or
Nifedipine on Thrombin-Induced Ca2+
Entry
Cells were exposed to thrombin (1.0 U/mL) for 180 seconds in
Ca2+-free medium followed by addition of 2
mmol/L CaCl2. Thrombin induced an increase
in the [Ca2+]i of cells incubated in
Ca2+-free PSS containing nominally zero or
standard external Mg2+ concentration (Fig 1A). The maximal response of
[Ca2+]i to thrombin was achieved within 15
seconds and returned to baseline within 180 seconds. No significant
differences in the basal [Ca2+]i, peak
[Ca2+]i, or [Ca2+]i
before addition of CaCl2
(pre-Ca2+ value of
[Ca2+]i) were observed between cells incubated
in nominally zero and standard Mg2+ solutions
(Table 2). Thrombin-evoked
Ca2+ entry, defined as the difference between
pre-Ca2+ values of
[Ca2+]i and the [Ca2+]i
after addition of CaCl2
(post-Ca2+ values), was significantly inhibited
by reduced external Mg2+ concentration (Fig 1A
and Table 2). Blockade of L-type Ca2+ channels
with nifedipine (1 µmol/L) did not cause a
significant reduction in thrombin-evoked Ca2+
entry in standard Mg2+ solution (Fig 1B).
|
) and standard
Mg2+ (1 mmol/L Mg2+, 
) concentrations
on thrombin-induced Ca2+ entry. Cells in
Ca2+-free medium containing nominally zero or standard
Mg2+ were stimulated with thrombin (1.0 U/mL) for 180
seconds then Ca2+ (2 mmol/L) was added (as indicated
by the arrow). The increase in cytosolic free Ca2+
concentration ([Ca2+]i) after addition of
Ca2+ to the medium was defined as the parameter
of the thrombin-induced Ca2+ entry. B, Typical trace
showing the effect of 1 µmol/L nifedipine on 1.0
U/mL of thrombin-induced Ca2+ entry. Nifedipine
was applied (as indicated by the arrow) after the addition of
Ca2+ (2 mmol/L) and did not affect the
Ca2+ entry.
|
Effect of Thrombin on Mobilization of Ca2+ From
Intracellular Stores
To evaluate the ability of thrombin to mobilize
Ca2+ from intracellular stores, the effect on
[Ca2+]i of sequential additions of thrombin and
thapsigargin, a selective inhibitor of the sarcoplasmic
reticulum Ca2+-ATPase,15
was investigated in Ca2+-free medium. Cells were
stimulated with 1.0 U/mL of thrombin in Ca2+-free
PSS with standard Mg.2+ After
[Ca2+]i had returned to baseline (36.5±3.0
nmol/L; n=4) from peak values (339.4±41.9 nmol/L),
1 µmol/L thapsigargin was added to the medium. The
[Ca2+]i slowly increased to a maximum
concentration of 98.6±11.1 nmol/L within 100 seconds.
Thapsigargin was found to mobilize a significant portion of
Ca2+ from intracellular
Ca2+ stores remaining after stimulation with 1.0
U/mL of thrombin.
Effect of Reduced Levels of Extracellular Mg2+ on
Capacitative Ca2+ Entry
Intracellular Ca2+ stores were depleted by
thapsigargin (1 µmol/L) to investigate capacitative
Ca2+ entry.11,16 Exposure
of ECs to 1 µmol/L thapsigargin induced an increase in
[Ca2+]i in Ca2+-free PSS.
The peak [Ca2+]i response was observed
approximately 100 seconds after introduction of drug. Values returned
to baseline after approximately 10 minutes (Fig 2). The intracellular
Ca2+ stores were thoroughly depleted by this
procedure since subsequent addition of 1 µmol/L ionomycin
failed to evoke further detectable Ca2+
mobilization (data not shown). After thapsigargin-induced depletion of
intracellular Ca2+ stores, addition of
CaCl2 to the medium caused substantial
capacitative Ca2+
entry11,16 (Fig 2).
Ca2+-induced Ca2+ release
from the internal Ca2+ stores presumably was not
a factor because the Ca2+ stores were depleted.
In the absence of extracellular Ca,2+ there was
no significant difference in the basal [Ca2+]i
or the Ca2+ transient induced by thapsigargin
(peak and the following baseline) between cells in buffer with
nominally zero and standard external Mg2+
concentrations (Table 3). The magnitude
of the capacitative Ca2+ entry, the difference
between pre-Ca2+ and
post-Ca2+ values, was significantly increased in
buffer with nominally zero external Mg2+
concentration (Table 3). In standard Mg2+ buffer,
Ca2+ entry was greater after treatment with
thapsigargin than after treatment with thrombin (n=5,
P<.05).
|
|
Effect of Elevated Extracellular Mg2+ Concentrations on
Thrombin-Induced Ca2+ Entry
To examine the effect of elevated external
Mg2+ concentrations on thrombin-induced
Ca2+ entry, MgSO4 was
cumulatively applied (3 to 30 mmol/L) during the
Ca2+ entry state of experiments initiated in
standard Mg2+ buffer (Fig 3A). The Ca2+ entry
was measured 50 seconds after introduction of each dose of
MgSO4. The Ca2+ entry
stimulated by 1.0 U/mL thrombin was inhibited in a
concentration-dependent manner by cumulative addition of
MgSO4 (Fig 3A). The inhibition of
thrombin-induced Ca2+ entry evoked by elevated
external Mg2+ concentrations was expressed as a
percentage of values obtained in standard Mg2+
solution at the corresponding time point (Fig 3B).
|
Effect of Elevated Extracellular Mg2+ Concentrations on
Capacitative Ca2+ Entry
The procedure for examining the effect of elevated external
Mg2+ concentrations on thapsigargin-induced
Ca2+ entry was similar to that for
thrombin-induced entry. Similar to the effect on thrombin-induced
entry, elevated external Mg2+ concentrations
inhibited capacitative Ca2+ entry in a
concentration-dependent manner (Fig 4).
|
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
The major findings of this study were (1) thrombin-evoked Ca2+ entry was inhibited by not only elevated but also low external Mg2+ concentrations, and (2) capacitative Ca2+ entry induced by thapsigargin was found to be inhibited by elevated external Mg2+ and augmented by decreased external Mg2+ concentration.
In cardiac myocytes and vascular smooth muscle cells, there is a general agreement concerning the inhibitory effect of external Mg2+ on Ca2+ influx9,17; however, the data derived from studies about the effects of internal Mg2+ on Ca2+ influx are controversial, with some investigators suggesting a direct and positive relationship between [Mg2+]i and Ca2+ influx,18 and others suggesting an inverse relationship.19,20 Therefore, the possibility exists that Mg2+ has different effects on Ca2+ influx between inside and outside of the cells. Moreover, previous studies have demonstrated the extremely low permeability of the cell membrane to Mg2+ because the ion has a large hydrated size and is highly polarized.17 Thus, the effects of extracellular Mg2+ and intracellular Mg2+ on Ca2+ influx must be addressed separately. In this study, short-term incubation of ECs in medium containing extracellular Mg2+ concentrations ranging from nominally 0 to 30 mmol/L did not induce changes in [Mg2+]i. Therefore, the effect of external Mg2+ concentration on Ca2+ influx was mediated by its direct action from the extracellular side but not its indirect action from the intracellular side. Net Ca2+ movement through the plasma membrane is determined by the differences between Ca2+ influx and efflux. Since Mg2+ in the cytosol is required for Ca2+-ATPase activity21 and [Mg2+]i was constant during the protocol, Ca2+ efflux appears to have been constant regardless of the extracellular Mg2+ concentrations. Therefore, the change in [Ca2+]i caused by the addition of CaCl2 to cells pretreated with thrombin or thapsigargin was attributed to the change in Ca2+ influx.
In ECs, receptor agonists such as thrombin induce an initial release of Ca2+ from intracellular stores followed by sustained entry of extracellular Ca2+.5 ECs have been reported to lack voltage-gated Ca2+ channels,3,10 and nifedipine did not affect the thrombin-induced Ca2+ influx in this study. Also, Ca2+ influx into ECs is not affected by Na+/Ca2+ exchange mechanisms.22,23 The increase in [Ca2+]i evoked by release from intracellular stores induces cell hyperpolarization via activation of Ca2+-activated K+ channels.24 Changes in the cell membrane potential play an important role in the regulation of Ca2+ influx in ECs. Cell hyperpolarization increases the electrochemical gradient for Ca2+ influx via a nonselective cation channel.3,25 Hyperpolarization-induced Ca2+ influx parallels agonist-induced Ca2+ influx.3 In this study, agonist-induced Ca2+ influx required external Mg,2+ but was inhibited by increased external Mg2+ in human ECs, consistent with observations of Yamamoto et al26 that high external Mg2+ directly blocked the nonselective cation channels in ECs of rat intrapulmonary artery. However, the effect of low external Mg2+ concentration on Ca2+ influx in ECs has not been examined in detail. Low external Mg2+ concentration may directly inhibit nonselective cation channels or Ca2+-activated K+ channels in human coronary ECs. The cell resting potential is maintained primarily by inwardly rectifying K+ channels.3,27 External Mg2+ inactivates the inwardly rectifying K+ channels in ECs, and the inactivation is largely eliminated in Mg2+-free buffer.28 Therefore, low external Mg2+ concentrations activate the inwardly rectifying K+ channels and hyperpolarize resting potential. The magnitude of the hyperpolarization, which parallels the agonist-induced Ca2+ influx,3 depends on the resting potential. In cells with deep resting potential, agonists induce a smaller hyperpolarization, thus decreasing the Ca2+ influx.29,30 Although a low external Mg2+ concentration has been reported to accelerate the receptor-operated Ca2+ influx in vascular smooth muscle cells,9 low external Mg2+ concentrations blocked the Ca2+ influx in human coronary arterial ECs in this study. Consistent with these data, both increased and decreased extracellular Mg2+ concentrations has been reported to attenuate the agonist-induced endothelium-dependent relaxation in isolated coronary and cerebral arteries.31,32
Capacitative Ca2+ entry has been studied in various cells types including vascular smooth muscle cells and nonexcitable cells such as ECs.9,33 Activation of capacitative Ca2+ entry by depleted stores requires neither continued receptor occupation nor elevations of inositol phosphates.33 In this study, capacitative Ca2+ entry was measured after the intracellular stores were completely emptied by exposure to thapsigargin in Ca2+-free medium. Thapsigargin mobilizes intracellular Ca2+ in the absence of receptor activation and inositol 1,4,5-trisphosphate formation.11,16 Therefore, a rapid rise in [Ca2+]i caused by the addition of CaCl2 to cells pretreated with thapsigargin was thought to represent capacitative Ca2+ entry. However, the precise mechanism and influx pathway have not been elucidated.33 Consistent with data from this laboratory indicating that capacitative Ca2+ entry is increased by low external Mg2+ and decreased by high external Mg2+ in rat vascular smooth muscle cells,9 capacitative Ca2+ entry was inhibited in proportion to the increase in external Mg2+ concentration in human coronary ECs.
Because Ca2+ is released from the intracellular stores after stimulation with thrombin and capacitative Ca2+ entry is enhanced by cell hyperpolarization,27,34 it is conceivable that the capacitative Ca2+ entry makes a contribution to the thrombin-induced Ca2+ influx pathway. However, in this study, the Ca2+ influx induced by thapsigargin (capacitative Ca2+ entry) exceeded that induced by thrombin. This difference may be due to suppression of refilling of intracellular Ca2+ stores in thapsigargin-treated cells by the inhibition of the sarcoplasmic reticulum Ca2+-ATPase. Protein kinase C is reported to be critical to capacitative Ca2+ entry inactivation.35 Protein kinase C produced by thrombin may inhibit capacitative Ca2+ entry. Moreover, intracellular Ca2+ stores were not fully depleted by 1.0 U/mL thrombin because subsequent exposure to 1 µmol/L thapsigargin induced a significant increase in [Ca2+]i. Therefore, capacitative Ca2+ entry may not have a major role in the entry pathway linked to thrombin receptors.
In summary, these results suggest that thrombin-induced Ca2+ requires external Mg2+ but is inhibited by high external Mg2+ concentration and that capacitative Ca2+ entry is reduced by elevated external Mg2+ concentration in human coronary arterial ECs.
|
Selected Abbreviations and Acronyms |
|---|
|
|
Acknowledgments |
|---|
The authors thank Dr Kaoru Yamaoka and Dr Takahiro Iwamoto for their excellent technical assistance. This study was supported by Grants-in-Aid for Scientific Research 06304028, 07407065, and 08457639 from the Ministry of Education, Science and Culture of Japan.
Received May 8, 1997; accepted July 8, 1997.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. Furchgott RF, Zawadzki JV. The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine. Nature. 1980;288:373–376.[Medline] [Order article via Infotrieve]
2. Moncada S, Palmer RMJ, Higgs EA. Nitric oxide: physiology, pathophysiology, and pharmacology. Pharmacol Rev. 1991;43:109–142.[Medline] [Order article via Infotrieve]
3.
Himmel HM, Whorton AR, Strauss HC. Intracellular
calcium, currents, and stimulus-response coupling in
endothelial cells. Hypertension. 1993;21:112–127.
4.
Buckley BJ, Mirza Z, Whorton AR. Regulation of
Ca2+-dependent nitric oxide synthase in bovine
aortic endothelial cells. Am J Physiol. 1995;269:C757–C765.
5.
Goligorsky MS, Menton DN, Laszlo A, Lum N. Nature of
thrombin-induced sustained increase in cytosolic calcium concentration
in cultured endothelial cells. J Biol
Chem. 1989;264:16771–16775.
6.
Wang Y, Shin WS, Kawaguchi H, Inukai M, Kato M,
Sakamoto A, Uehara Y, Miyamoto M, Shimamoto N, Korenaga R, Ando J,
Toyo-oka T. Contribution of sustained Ca2+
elevation for nitric oxide production in
endothelial cells and subsequent modulation of
Ca2+ transient in vascular smooth muscle cells in
coculture. J Biol Chem. 1992;267:20377–20382.
7. Reinhart RA. Clinical correlates of the molecular and cellular actions of magnesium on the cardiovascular system. Am Heart J. 1991;121:1513–1521.[Medline] [Order article via Infotrieve]
8. Resnick LM. Cellular calcium and magnesium metabolism in the pathophysiology and treatment of hypertension and related metabolic disorders. Am J Med. 1992;93(suppl 2A):11S–20S.
9.
Yoshimura M, Oshima T, Matsuura H, Ishida T, Kambe M,
Kajiyama G. Extracellular Mg2+ inhibits
capacitative Ca2+ entry in vascular smooth muscle
cells. Circulation. 1997;95:2567–2572.
10.
Cannell MB, Sage SO. Bradykinin-evoked changes in
cytosolic calcium and membrane currents in cultured bovine
pulmonary artery endothelial cells.
J Physiol (Lond). 1989;419:555–568.
11. Schilling WP, Cabello OA, Rajan L. Depletion of the inositol 1,4,5-trisphosphate-sensitive intracellular Ca2+ store in vascular endothelial cells activates the agonist-sensitive Ca2+-influx pathway. Biochem J. 1992;284:521–530.
12. van Ijzendoorm SCD, van Gool RGJ, Reutelingsperger CPM, Heemskerk JWM. Unstimulated platelets evoke calcium response in human umbilical vein endothelial cells. Biochim Biophys Acta. 1996;1311:64–70.[Medline] [Order article via Infotrieve]
13.
Grynkiewicz G, Poenie M, Tsien RY. A new generation of
calcium indicators with greatly improved fluorescence
properties. J Biol Chem. 1985;260:3440–3450.
14.
Raju B, Murphy E, Levy LA. A fluorescent
indicator for measuring cytosolic free magnesium. Am J
Physiol. 1989;256:C540–C548.
15.
Sagara Y, Inesi G. Inhibition of the sarcoplasmic
reticulum Ca2+ transport ATPase by thapsigargin
at subnanomolar concentrations. J Biol Chem. 1991;266:13503–13506.
16.
Dolor RJ, Hurwitz LM, Mirza Z, Strauss HC, Whorton AR.
Regulation of extracellular Ca2+ entry in
endothelial cells: role of intracellular
Ca2+ pools. Am J Physiol. 1992;262:C171–C181.
17. Flatman PW. Mechanisms of magnesium transport. Annu Rev Physiol. 1991;53:259–271.[Medline] [Order article via Infotrieve]
18. Yoshimura M, Oshima T, Matsuura H, Ishida T, Kambe M, Kajiyama G. Potentiation of intracellular Ca2+ response to arginine vasopressin by increased cytosolic-free Mg2+ in rat vascular smooth muscle cells. Biochim Biophys Acta. 1996;1312:151–157.[Medline] [Order article via Infotrieve]
19.
White RE, Hartzell HC. Effects of intracellular free
magnesium on calcium current in isolated cardiac myocytes.
Science. 1988;239:778–780.
20. Yamaoka K, Seyama I. Regulation of Ca channel by intracellular Ca2+ and Mg2+ in frog ventricular cells. Pflügers Arch. 1996;431:305–317.[Medline] [Order article via Infotrieve]
21. Arsenian MA. Magnesium and cardiovascular disease. Prog Cardiovasc Dis. 1993;35:271–310.[Medline] [Order article via Infotrieve]
22.
Schilling WP, Ritchie AK, Navarro LT, Eskin SG.
Bradykinin-stimulated calcium influx in cultured bovine aortic
endothelial cells. Am J Physiol. 1988;255:H219–H227.
23.
Graier WF, Simecek S, Sturek M. Cytochrome P450
mono-oxygenase-regulated signalling of
Ca2+ entry in human and bovine
endothelial cells. J Physiol (Lond). 1995;482:259–274.
24. Vaca L, Schilling WP, Kunze DL. G-protein-mediated regulation of a Ca2+-dependent K+ channel in cultured vascular endothelial cells. Pflügers Arch. 1992;422:66–74.[Medline] [Order article via Infotrieve]
25. Manabe K, Takano M, Noma A. Non-selective cation current of guinea-pig endocardial endothelial cells. J Physiol (Lond). 1995;487(2):407–419.
26.
Yamamoto Y, Chen G, Miwa K, Suzuki H. Permeability and
Mg2+ blockade of histamine-operated cation
channel in endothelial cells of rat
intrapulmonary artery. J Physiol (Lond). 1992;450:395–408.
27.
Vaca L, Licea A, Possani LD. Modulation of cell
membrane potential in cultured vascular endothelium.
Am J Physiol. 1996;270:C819–C824.
28.
Elam TR, Lansman JB. The role of
Mg2+ in the inactivation of inwardly rectifying
K+ channels in aortic endothelial
cells. J Gen Physiol. 1995;105:463–484.
29.
Mehrke G, Pohl U, Daut J. Effects of vasoactive
agonists on the membrane potential of cultured bovine aortic and
guinea-pig coronary endothelium. J
Physiol (Lond). 1991;439:277–299.
30. Lückhoff A, Busse R. Calcium influx into endothelial cells and formation of endothelium-derived relaxing factor is controlled by the membrane potential. Pflügers Arch. 1990;416:305–311.[Medline] [Order article via Infotrieve]
31. Ku DD, Ann HS. Differential effects of magnesium on basal and agonist-induced EDRF relaxation in canine coronary arteries. J Cardiovasc Pharmacol. 1991;17:999–1006.[Medline] [Order article via Infotrieve]
32. Faragó M, Szabó C, Dóra E, Horváth I, Kovách AGB. Contractile and endothelium-dependent dilatory responses of cerebral arteries at various extracellular magnesium concentrations. J Cereb Blood Flow Metab. 1991;11:161–164.[Medline] [Order article via Infotrieve]
33. Putney JW Jr, Bird GStJ. The signal for capacitative calcium entry. Cell. 1993;75:199–201.[Medline] [Order article via Infotrieve]
34.
Laskey RE, Adams DJ, Johns A, Rubanyi GM, van Breemen
C. Membrane potential and
Na+-K+ pump activity
modulate resting and bradykinin-stimulated changes in cytosolic free
calcium in cultured endothelial cells from bovine
atria. J Biol Chem. 1990;265:2613–2619.
35.
Parekh AB, Penner R. Activation and inactivation
mechanisms of capacitative calcium influx. Proc Natl Acad Sci
U S A. 1995;92:7907–7911.
This article has been cited by other articles:
 |
|
 |
|
  E. D. Motley, K. Eguchi, M. M. Patterson, P. D. Palmer, H. Suzuki, and S. Eguchi Mechanism of Endothelial Nitric Oxide Synthase Phosphorylation and Activation by Thrombin Hypertension, March 1, 2007; 49(3): 577 - 583. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||