Vol. 173, No. 3, 1990
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS Pages 1038-1042
December 31, 1990
STRETCH MAY ENHANCE THE RELEASE OF ENDOTHELIUM-DERIVED RELAXING FACTOR IN RABBIT AORTA Minoru 0hno, Masahiko Ochiai, Junichi Taguchi, Kazuhiro Hara, Nobuharu Akatsuka, and Kiyoshi Kurokawa First Department of Internal Medicine The University of Tokyo, Faculty of Medicine 7-3-1 Hongo, Bunkyo-ku, Tokyo ].13, Japan Received October 23, 1990
The effect of vascular stretch on the release of EDRF was studied by measuring tissue cGMP levels of rabbit. Aortic rings of rabbit were quick-frozen in liquid nitrogen during varying resting tensions, and cGMP contents were determined by radio-immunoassay. The tissue cGMP levels significantly elevated with the increase in resting tension in endothelium-intact rings, but not in endothelium-denuded rings. Deprivation of extracellular calcium abolished the stretch-induced elevation of tissue cGMP levels in endothelium-intact segments. These stretch-induced endothellum dependent tissue cGMP elevations were unaffected by Ca 2+ channel blockers, nicardipine and diltiazem. Data suggest that vascular stretch may release EDRF via mechanism dependent on extracellular calcium, but probably not through voltage-dependent calcium channel. © 1990 A c a d e m i c
The
Press,
vascular
regulation endothelin, EDRF
is
Inc.
of and
thought
endothelium
blood
vessel
plays tone
an by
endothelium-derived to relax
important releasing
relaxing
the vascular
role
in
the
prostaglandins,
factor
smooth muscle
(EDRF)(I-3). cells
through
activation of soluble guanylate cyclase leading to a rise in cGMP (4, 5). The release of EDRF is thought to be stimulated by many agents as well as by physical stimuli such as sheer stress by blood flow (I, 2, 6, 7).
However,
it is not clear
if the stretching
tissue due to blood pressure causes the release of EDRF.
of vascular Therefore,
we studied this issue by measuring tissue cGMP levels in rabbit aorta.
MATERIALS and METHODS Male rabbits (2-2.5 kg) were killed with a single intravenous injection of sodium pentobarbital (30-35 mg/kg), and thoracic and abdominal aorta were carefully dissected from surrounding tissue. 0006-291X/90 $1.50 Copyright © 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.
1038
Vol. 173, No. 3, 1990
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Rabbit aortic ring segments (4 mm wide) with and without endothelium were used in the experiments. The segments without endothelium were made by gently rubbing the intimal surface with a cotton stick. The aortic rings were mounted under a resting tension of 1 gr. on stainless-steel hooks in i0 ml muscle chambers and bathed in Tyrode solution bubbled with the gas mixture: 02 95%/C02 5% at 37°C. The composition of Tyrode solution was (in mM): NaCI 137.9, KCI 2.7, CaCI 2 1.8, MgCI 2 0.5, NaHCO 3 11.9, and glucose 5.6. Tensions were measured isometrically, using Nihon Kohden Co. Ltd. force-tranceducer TB 611T and Nippon Denki San-ei Co. Ltd. amplifier. Tissues were equilibrated for 120 min before experiments. Successful preservation and removal of endothelium were respectively confirmed by the ability and the inability of 10-6M acetylcholine to induce relaxation of the contraction induced by 10-6M norepinephrine. After the tissues were washed, three times, with Tyrode solution, experiments were performed as follows: Experiment l: Effect of the stretch on cGMP levels. Each segment was kept under varying resting tension for 30 min, because it required at least i0 minutes to get stabilized resting tension. Thereafter, the segments were quickly taken out together with the hooks and mounts, and immediately frozen in liquid nitrogen. It took approximately 1 second to carry out the procedure. The frozen segments were homogenized in trichloroacetic acid. The tissue homogenate was centrifuged at 1,000 g for 5 min and the cGMP content of each supernatent Was determined by radio-immunoassay (YamasaShoyu, Tokyo). The cGMP levels were expressed as fmol/mg wet weight. Experiment 2: Effect of calcium free medium on cGMP levels induced by stretching. Tissue cGMP levels were determined in aortic rings with and without endothelium, which were kept under 0 gr or 2 gr resting tension for 30 minutes, in the presense and absense of extracellular calcium. Experiment 3: Effect of nicardipine and levels induced by stretching. The effect blockers on stretch-induced tissue cGMP levels were kept under resting tension of 0 gr or 2 nicardipine, 10-7M-10-5M, or diltiazem, 10-bM.
diltiazem on the cGMP of two Ca 2+ channel were studied. Tissues gr in the presense of
Statistical analysis: The data are expressed as the means and SEMs in the text and figures. Statistical significance was assessed by using Student's t test, and p value less than 0.05 was considered significant.
RESULTS Tissue
cGMP
levels
of
endothelium-intact
segments
significantly higher than those of endothelium-denuded without
the
weight). resting
The
resting
tension
(29.2+2.8
tissue cGMP levels
vs
segments
cGMP levels reached a plateau at a resting cGMP
level
of
significantly
in
medium,
cGMP
the
endothelium-denuded response levels
to of
stretch the
1039
segments even
19.9+2.6
increased with
tension in endothelium-intact
were
fmol/mg
an increase
(Fig i).
in the
The tissue
tension of 2 gr.
segments (Fig.
did i).
wet
Tissue
not In
endothelium-intact
change
Ca 2+
free
segments
V o l . 173, N o . 3, 1 9 9 0
50 40
o
BIOCHEMICAL A N D BIOPHYSICAL RESEARCH C O M M U N I C A T I O N S
80
~
E(+} n = 1 0
70
~D
6O
E E (+)(-)
50
~ 40
30
Q..
~ 2o
~ 3o
. ~E(-) n= S
20
(D
10
® 0.'5
i
115 P
3
resting Og tension
,5 (9)
2~
Og
control
2
C a ++ f r e e
Fig. i. Effect of varying resting tension on tissue cGMP levels. The rabbit aortic rings with endothelium:E(+) and without endothelinm:E(-) were kept under varying resting tensions for 30 minutes. Each segment was quickly taken out and frozen in liquid nitrogen, and tissue cGMP levels were determined by the RIA method. Each point respectively expresses the means and SEM of the samples. Tissue cGMP levels of E(+) segments were significantly higher than those of E(-) segments without resting tension. The tissue cGMP levels increased with resting tension and reached a peak at the resting tension of 2 gr in E(+) segments. On the contrary, the tissue cGMP levels of E(-) segments were unaffected hy the change in resting tension. Fig. 2. The effect of Ca2+-free medium on stretch-induced tissue cGMP elevation. Endothelium-intact:E(+) and endothelium-denuded:E(-) segments were kept under the resting tension of 0 gr or 2 gr in Tyrode solution (Control) or calcium-free medium for 30 min. Thereafter, tissue cGMP levels were determined as mentioned in Fig i. Each bar expresses the mean and SEM of the tissue cGMP levels of samples over 5. Ca2+-free medium abolished tissue cGMP elevation by both the presence of endothelium and increase of the resting tension.
decreased.
Moreover,
endothelium-intact (Fig. 2).
the
segments
By contrast,
segments
was
diltiazem
had
not no
increase was
cGMP levels
abolished
in
Ca 2+
by
stretch
free
of
solution
the tissue cGMP levels of endothelium-denuded
affected effect
in the
on
by
C7 +
free
medium.
Nicardipine
the
endothelium-dependent
and
cGMP elevation
by stretch (Table i).
DISCUSSION Endothelium releasing
several
mechanical example,
thought
contractile
to
regulate
blood
and
relaxant
factors
vessel in
stimuli such as blood flow and blood pressure
tone
by
response
to
(7, 8).
For
EDRF is released in response to sheer stress by blood flow.
The mechanism unknown.
is
by which
However,
blood
flow
available
data
regulates
1040
suggest
the an
release
of
association
EDRF of
is
EDRF
Vol. 173, No. 3, 1990
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Table1. Effect of nicardipine and diltiazern on the tissue cGMP levels oonditions resting tension
cGMP (fmol/g w.w.) Nicardipine10-7M Nicardipine1O-6MNicardipine104M Diltiazern10-5M
control
0g
34.1+3.| (lo)
32.7+4.0 (lo)
36.4+4.4 (lo)
33.2+3.5 (lo)
32.1---4.3 (lo)
2g
56.5+3.5 (10)
50.9+3.8 (To)
54.5_+5.3 (10)
58.4+4.0 (10)
58.1 +4.6 (10)
0g
18.1+4.2 (5)
19.8+3.6 (5)
20.1+4.2 (5)
21.0+4.0 (5)
20.1+4.0 (5)
2g
19.7+3.8 (5)
20.4-+4.1 (5)
20.1-+2.8 (5)
20.1_+4.3 (5)
21.1_+3.2 (5)
E(+)
E(--)
Tissues were kept with the resting tension of 0 gr or 2 gr with nieardipine 10-6M, 10-5M or diltiazem 10-bM for 30 minutes and thereafter tissue cGMP levels were determined. Values are expressed as means and SEM. The numbers in parenthesis mean the number of sample. Ca2+ channel blockers had no influence on the endothelium dependent tissue cGMP elevation induced by stretching.
release
with
in response
a hyperpolarization to flow
blood pressure inward
cation
(9).
endothelial
Stretching
may be another channel
of
of the endothelial
stimulus
activation
membrane
for releasing
potential
membrane
by
EDRF through an
which
allows
inward
cGMP
levels
in
calcium
influx
(2, 10). Our
results
showed
that
segments were
significantly
segments
without
thought
even to be
due
that
increase
resting
results
in
raise
the release the
the
may
resting
tension.
in
possibility
soluble
smooth muscle
levels.
we also
Therefore,
tissue
cGMP
levels
similarly to EDRF, elevate
cGMP
stretch
had
nitroglycerin
the
there
pathway in vascular
the
EDRF
elevation (4).
Our
elevated
stretch
studied
These
of
tissue
activates
possibility
cyclase
the effect
by
is
also
segments.
by
cells and may increase
elevated
cGMP
to an
may be another guanylate
of
results
in response
endothelium-intact
that
However
activate
This
of
cGMP levels
tension
endothelium-intact
than those in endothelium-denuded
release
the tissue
of EDRF.
stretch
higher
to basal
demonstrated
the
an
unknown
tissue cGMP
of tissue
nitroglycerin.
that
stretch on
Nitroglycerin,
is known to activate soluble guanylate cyclase and
levels no
in
vascular
effect
(Data not
on
the
shown).
smooth tissue
These
muscle cGMP
results
cells.
However,
levels
induced
by
strongly
support
the
hypothesis that stretch enhances the release of EDRF. We minutes
studied after
stabilized
the
tissue
cGMP
resting t e n s i o n
resting
tension
at
was
concentration loaded,
this time
1041
of
because
point.
time we
However,
point could the
30 get
change
Vol. 173, No. 3, 1990
of tissue
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
cGMP concentration
in response
to acute
stretch and long
term stretch also remains for further investigation. Deprivation
of
extracellular
calcium
inhibited
the
tissue cGMP induced not only by basal release of EDRF, stretch-released EDRF in endothelium-intact segments. of soluble guanylate
rise
of
but also by
The activation
cyclase does not require extracellular calcium,
as calclum-free medium did not inhibit the elevation of tissue cGMP levels the
by nitroglycerin
suppression of
in our study
tissue
cGMP of
(Data not
shown).
endothelium-intact
Therefore, segments in
calcium free medium is thought to be due to the suppression of EDRF release.
Then,
necessary
not
extracellular
only
for
the
calcium basal
entry
release
enhanced release of EDRF by stretch.
is
of
thought
EDRF
but
to
also
be for
These data suggest stretch may
release EDRF via mechanism dependent on extracellular calcium. What entry?
pathway Our
effect
on
release pathways,
result
the
is
tissue
of EDRF.
responsible
showed
that
for
cGMP elevation
These
results
not voltage-dependent
the
nicardipine
raise
by
stretch-induced and
basal
diltiazem
and
had
no
stretch-induced
the possibility
calcium channels,
calcium
that unknown
may be involved in
the stretch-induced calcium entry in endothelial cells.
REFERENCES (i) (2) (3) (4) (5) (6) (7) (8) (9) (i0)
Furchgott R.F., Zawadzki J.V. Nature 288:373-376 (1980) Furchgott R.F. Cir. Res. 53:557-573 (1983) Yanagisawa M., Kurihara H. et al Nature (Lond). 332:411-415 Rapoport R.M., Murad F. Cir. Res. 52:352-357 (1983) Murad F. J. Cli. Invest. 7 8 : 1 - 5 (1986) Rubanyi G.M., Romero J.C., Vanhoutte P.M. Am. J. Physiol. 250: HI145-I149 (1986) Lansman J.B. Nature 331:481-482 (1988) Davies F.D. News in Physiological Sciences 4 : 2 2 - 4 0 (1989) Olsens S. P., Clapham., Davies P.F. Nature 331:168-170 (1988) Lansman J.B., Hallam T.J., Rink T.J. Nature 325:811-813 (1987)
1042
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS Pages 1038-1042
December 31, 1990
STRETCH MAY ENHANCE THE RELEASE OF ENDOTHELIUM-DERIVED RELAXING FACTOR IN RABBIT AORTA Minoru 0hno, Masahiko Ochiai, Junichi Taguchi, Kazuhiro Hara, Nobuharu Akatsuka, and Kiyoshi Kurokawa First Department of Internal Medicine The University of Tokyo, Faculty of Medicine 7-3-1 Hongo, Bunkyo-ku, Tokyo ].13, Japan Received October 23, 1990
The effect of vascular stretch on the release of EDRF was studied by measuring tissue cGMP levels of rabbit. Aortic rings of rabbit were quick-frozen in liquid nitrogen during varying resting tensions, and cGMP contents were determined by radio-immunoassay. The tissue cGMP levels significantly elevated with the increase in resting tension in endothelium-intact rings, but not in endothelium-denuded rings. Deprivation of extracellular calcium abolished the stretch-induced elevation of tissue cGMP levels in endothelium-intact segments. These stretch-induced endothellum dependent tissue cGMP elevations were unaffected by Ca 2+ channel blockers, nicardipine and diltiazem. Data suggest that vascular stretch may release EDRF via mechanism dependent on extracellular calcium, but probably not through voltage-dependent calcium channel. © 1990 A c a d e m i c
The
Press,
vascular
regulation endothelin, EDRF
is
Inc.
of and
thought
endothelium
blood
vessel
plays tone
an by
endothelium-derived to relax
important releasing
relaxing
the vascular
role
in
the
prostaglandins,
factor
smooth muscle
(EDRF)(I-3). cells
through
activation of soluble guanylate cyclase leading to a rise in cGMP (4, 5). The release of EDRF is thought to be stimulated by many agents as well as by physical stimuli such as sheer stress by blood flow (I, 2, 6, 7).
However,
it is not clear
if the stretching
tissue due to blood pressure causes the release of EDRF.
of vascular Therefore,
we studied this issue by measuring tissue cGMP levels in rabbit aorta.
MATERIALS and METHODS Male rabbits (2-2.5 kg) were killed with a single intravenous injection of sodium pentobarbital (30-35 mg/kg), and thoracic and abdominal aorta were carefully dissected from surrounding tissue. 0006-291X/90 $1.50 Copyright © 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.
1038
Vol. 173, No. 3, 1990
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Rabbit aortic ring segments (4 mm wide) with and without endothelium were used in the experiments. The segments without endothelium were made by gently rubbing the intimal surface with a cotton stick. The aortic rings were mounted under a resting tension of 1 gr. on stainless-steel hooks in i0 ml muscle chambers and bathed in Tyrode solution bubbled with the gas mixture: 02 95%/C02 5% at 37°C. The composition of Tyrode solution was (in mM): NaCI 137.9, KCI 2.7, CaCI 2 1.8, MgCI 2 0.5, NaHCO 3 11.9, and glucose 5.6. Tensions were measured isometrically, using Nihon Kohden Co. Ltd. force-tranceducer TB 611T and Nippon Denki San-ei Co. Ltd. amplifier. Tissues were equilibrated for 120 min before experiments. Successful preservation and removal of endothelium were respectively confirmed by the ability and the inability of 10-6M acetylcholine to induce relaxation of the contraction induced by 10-6M norepinephrine. After the tissues were washed, three times, with Tyrode solution, experiments were performed as follows: Experiment l: Effect of the stretch on cGMP levels. Each segment was kept under varying resting tension for 30 min, because it required at least i0 minutes to get stabilized resting tension. Thereafter, the segments were quickly taken out together with the hooks and mounts, and immediately frozen in liquid nitrogen. It took approximately 1 second to carry out the procedure. The frozen segments were homogenized in trichloroacetic acid. The tissue homogenate was centrifuged at 1,000 g for 5 min and the cGMP content of each supernatent Was determined by radio-immunoassay (YamasaShoyu, Tokyo). The cGMP levels were expressed as fmol/mg wet weight. Experiment 2: Effect of calcium free medium on cGMP levels induced by stretching. Tissue cGMP levels were determined in aortic rings with and without endothelium, which were kept under 0 gr or 2 gr resting tension for 30 minutes, in the presense and absense of extracellular calcium. Experiment 3: Effect of nicardipine and levels induced by stretching. The effect blockers on stretch-induced tissue cGMP levels were kept under resting tension of 0 gr or 2 nicardipine, 10-7M-10-5M, or diltiazem, 10-bM.
diltiazem on the cGMP of two Ca 2+ channel were studied. Tissues gr in the presense of
Statistical analysis: The data are expressed as the means and SEMs in the text and figures. Statistical significance was assessed by using Student's t test, and p value less than 0.05 was considered significant.
RESULTS Tissue
cGMP
levels
of
endothelium-intact
segments
significantly higher than those of endothelium-denuded without
the
weight). resting
The
resting
tension
(29.2+2.8
tissue cGMP levels
vs
segments
cGMP levels reached a plateau at a resting cGMP
level
of
significantly
in
medium,
cGMP
the
endothelium-denuded response levels
to of
stretch the
1039
segments even
19.9+2.6
increased with
tension in endothelium-intact
were
fmol/mg
an increase
(Fig i).
in the
The tissue
tension of 2 gr.
segments (Fig.
did i).
wet
Tissue
not In
endothelium-intact
change
Ca 2+
free
segments
V o l . 173, N o . 3, 1 9 9 0
50 40
o
BIOCHEMICAL A N D BIOPHYSICAL RESEARCH C O M M U N I C A T I O N S
80
~
E(+} n = 1 0
70
~D
6O
E E (+)(-)
50
~ 40
30
Q..
~ 2o
~ 3o
. ~E(-) n= S
20
(D
10
® 0.'5
i
115 P
3
resting Og tension
,5 (9)
2~
Og
control
2
C a ++ f r e e
Fig. i. Effect of varying resting tension on tissue cGMP levels. The rabbit aortic rings with endothelium:E(+) and without endothelinm:E(-) were kept under varying resting tensions for 30 minutes. Each segment was quickly taken out and frozen in liquid nitrogen, and tissue cGMP levels were determined by the RIA method. Each point respectively expresses the means and SEM of the samples. Tissue cGMP levels of E(+) segments were significantly higher than those of E(-) segments without resting tension. The tissue cGMP levels increased with resting tension and reached a peak at the resting tension of 2 gr in E(+) segments. On the contrary, the tissue cGMP levels of E(-) segments were unaffected hy the change in resting tension. Fig. 2. The effect of Ca2+-free medium on stretch-induced tissue cGMP elevation. Endothelium-intact:E(+) and endothelium-denuded:E(-) segments were kept under the resting tension of 0 gr or 2 gr in Tyrode solution (Control) or calcium-free medium for 30 min. Thereafter, tissue cGMP levels were determined as mentioned in Fig i. Each bar expresses the mean and SEM of the tissue cGMP levels of samples over 5. Ca2+-free medium abolished tissue cGMP elevation by both the presence of endothelium and increase of the resting tension.
decreased.
Moreover,
endothelium-intact (Fig. 2).
the
segments
By contrast,
segments
was
diltiazem
had
not no
increase was
cGMP levels
abolished
in
Ca 2+
by
stretch
free
of
solution
the tissue cGMP levels of endothelium-denuded
affected effect
in the
on
by
C7 +
free
medium.
Nicardipine
the
endothelium-dependent
and
cGMP elevation
by stretch (Table i).
DISCUSSION Endothelium releasing
several
mechanical example,
thought
contractile
to
regulate
blood
and
relaxant
factors
vessel in
stimuli such as blood flow and blood pressure
tone
by
response
to
(7, 8).
For
EDRF is released in response to sheer stress by blood flow.
The mechanism unknown.
is
by which
However,
blood
flow
available
data
regulates
1040
suggest
the an
release
of
association
EDRF of
is
EDRF
Vol. 173, No. 3, 1990
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Table1. Effect of nicardipine and diltiazern on the tissue cGMP levels oonditions resting tension
cGMP (fmol/g w.w.) Nicardipine10-7M Nicardipine1O-6MNicardipine104M Diltiazern10-5M
control
0g
34.1+3.| (lo)
32.7+4.0 (lo)
36.4+4.4 (lo)
33.2+3.5 (lo)
32.1---4.3 (lo)
2g
56.5+3.5 (10)
50.9+3.8 (To)
54.5_+5.3 (10)
58.4+4.0 (10)
58.1 +4.6 (10)
0g
18.1+4.2 (5)
19.8+3.6 (5)
20.1+4.2 (5)
21.0+4.0 (5)
20.1+4.0 (5)
2g
19.7+3.8 (5)
20.4-+4.1 (5)
20.1-+2.8 (5)
20.1_+4.3 (5)
21.1_+3.2 (5)
E(+)
E(--)
Tissues were kept with the resting tension of 0 gr or 2 gr with nieardipine 10-6M, 10-5M or diltiazem 10-bM for 30 minutes and thereafter tissue cGMP levels were determined. Values are expressed as means and SEM. The numbers in parenthesis mean the number of sample. Ca2+ channel blockers had no influence on the endothelium dependent tissue cGMP elevation induced by stretching.
release
with
in response
a hyperpolarization to flow
blood pressure inward
cation
(9).
endothelial
Stretching
may be another channel
of
of the endothelial
stimulus
activation
membrane
for releasing
potential
membrane
by
EDRF through an
which
allows
inward
cGMP
levels
in
calcium
influx
(2, 10). Our
results
showed
that
segments were
significantly
segments
without
thought
even to be
due
that
increase
resting
results
in
raise
the release the
the
may
resting
tension.
in
possibility
soluble
smooth muscle
levels.
we also
Therefore,
tissue
cGMP
levels
similarly to EDRF, elevate
cGMP
stretch
had
nitroglycerin
the
there
pathway in vascular
the
EDRF
elevation (4).
Our
elevated
stretch
studied
These
of
tissue
activates
possibility
cyclase
the effect
by
is
also
segments.
by
cells and may increase
elevated
cGMP
to an
may be another guanylate
of
results
in response
endothelium-intact
that
However
activate
This
of
cGMP levels
tension
endothelium-intact
than those in endothelium-denuded
release
the tissue
of EDRF.
stretch
higher
to basal
demonstrated
the
an
unknown
tissue cGMP
of tissue
nitroglycerin.
that
stretch on
Nitroglycerin,
is known to activate soluble guanylate cyclase and
levels no
in
vascular
effect
(Data not
on
the
shown).
smooth tissue
These
muscle cGMP
results
cells.
However,
levels
induced
by
strongly
support
the
hypothesis that stretch enhances the release of EDRF. We minutes
studied after
stabilized
the
tissue
cGMP
resting t e n s i o n
resting
tension
at
was
concentration loaded,
this time
1041
of
because
point.
time we
However,
point could the
30 get
change
Vol. 173, No. 3, 1990
of tissue
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
cGMP concentration
in response
to acute
stretch and long
term stretch also remains for further investigation. Deprivation
of
extracellular
calcium
inhibited
the
tissue cGMP induced not only by basal release of EDRF, stretch-released EDRF in endothelium-intact segments. of soluble guanylate
rise
of
but also by
The activation
cyclase does not require extracellular calcium,
as calclum-free medium did not inhibit the elevation of tissue cGMP levels the
by nitroglycerin
suppression of
in our study
tissue
cGMP of
(Data not
shown).
endothelium-intact
Therefore, segments in
calcium free medium is thought to be due to the suppression of EDRF release.
Then,
necessary
not
extracellular
only
for
the
calcium basal
entry
release
enhanced release of EDRF by stretch.
is
of
thought
EDRF
but
to
also
be for
These data suggest stretch may
release EDRF via mechanism dependent on extracellular calcium. What entry?
pathway Our
effect
on
release pathways,
result
the
is
tissue
of EDRF.
responsible
showed
that
for
cGMP elevation
These
results
not voltage-dependent
the
nicardipine
raise
by
stretch-induced and
basal
diltiazem
and
had
no
stretch-induced
the possibility
calcium channels,
calcium
that unknown
may be involved in
the stretch-induced calcium entry in endothelial cells.
REFERENCES (i) (2) (3) (4) (5) (6) (7) (8) (9) (i0)
Furchgott R.F., Zawadzki J.V. Nature 288:373-376 (1980) Furchgott R.F. Cir. Res. 53:557-573 (1983) Yanagisawa M., Kurihara H. et al Nature (Lond). 332:411-415 Rapoport R.M., Murad F. Cir. Res. 52:352-357 (1983) Murad F. J. Cli. Invest. 7 8 : 1 - 5 (1986) Rubanyi G.M., Romero J.C., Vanhoutte P.M. Am. J. Physiol. 250: HI145-I149 (1986) Lansman J.B. Nature 331:481-482 (1988) Davies F.D. News in Physiological Sciences 4 : 2 2 - 4 0 (1989) Olsens S. P., Clapham., Davies P.F. Nature 331:168-170 (1988) Lansman J.B., Hallam T.J., Rink T.J. Nature 325:811-813 (1987)
1042
