Suppression of cAMP by
phosphoinositol/Ca2+ pathway
in the cardiac
-opioid receptor
Wei-Min
Zhang and
Tak-Ming
Wong
Department of Physiology and Institute of Cardiovascular Science and
Medicine, Faculty of Medicine, The University of Hong Kong, Hong
Kong
 |
ABSTRACT |
To determine whether
the phosphoinositol/Ca2+ pathway
interacts with the adenylate cyclase/adenosine 3',5'-cyclic
monophosphate (cAMP) pathway in the cardiac
-receptor, the effects
of U-50488, a specific
-receptor agonist, on the intracellular
Ca2+ concentration
([Ca2+]i)
and forskolin-induced accumulation of cAMP in rat ventricular myocytes
were determined after interference of the
phosphoinositol/Ca2+ pathway.
U-50488 suppressed the forskolin-induced accumulation of cAMP and
elevated
[Ca2+]i,
which were blocked by norbinaltorphimine, a specific
-receptor antagonist, and pertussis toxin. The effects of U-50488 were
qualitatively similar to those of A-23187, a
Ca2+ ionophore, but opposite to
those of
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-acetoxymethyl ester (AM), a
[Ca2+]i
chelator. Abolition of U-50488-induced elevation of
[Ca2+]i
by BAPTA-AM also abolished the effect of U-50488 on forskolin-induced accumulation of cAMP. Inhibition of the phospholipase C by specific inhibitors, U-73122 and neomycin, abolished the effects of U-50488 on
both
[Ca2+]i
and forskolin-induced accumulation of cAMP. The results showed for the
first time that
-receptor stimulation may suppress cAMP accumulation
via activation of the
phosphoinositol/Ca2+ pathway in
the rat heart.
adenylate cyclase; intracellular calcium ion; phospholipase C; ventricular myocyte; adenosine 3',5'-cyclic monophosphate
 |
INTRODUCTION |
IT HAS BEEN SHOWN THAT activation of the phospholipase
C (PLC) leading to an increased production of inositol trisphosphate (IP3), which eventually results
in mobilization of Ca2+ from its
intracellular store, is accompanied by a reduction in adenosine
3',5'-cyclic monophosphate (cAMP) accumulation in a number
of receptors, such as bradykinin receptor in NCB-20 cells (4),
muscarinic receptor in the pregnant rat myometrium (12), substance K
receptor, and P2U-purinergic
receptor in C6-2B rat glioma cells (9, 25),
1-adrenergic receptor, and
endothelin receptor in the rat cardiac myocyte (5, 13). In these
receptors, the production of IP3
is inversely related to the accumulation of cAMP upon receptor
stimulation (4, 9, 12). The observations suggest a possible cross talk
between the two pathways. It has also been shown that the
receptor-mediated inhibition of cAMP accumulation is abolished by
thapsigargin and
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-acetoxymethyl ester (AM), which deplete
Ca2+ of its intracellular store
and cytosolic Ca2+ concentration
([Ca2+]i),
respectively (4, 9, 11, 12, 25), suggesting that intracellular
Ca2+ may mediate the suppressive
action of the phosphoinositol/Ca2+
pathway on the adenylate cyclase (AC)/cAMP pathway. In support of a
possible mediating role of Ca2+ on
the AC/cAMP pathway,
[Ca2+]i
at a submicromolar concentration range inhibits
Ca2+-inhibitable AC in many
tissues, including cardiac sarcolemma (6, 27). This is further
supported by the successful cloning and expression of
Ca2+-inhibitable AC (2, 16, 18,
19, 42).
In the heart, stimulation of the
-receptor by specific
-receptor
agonist suppresses cAMP (41) and activates PLC, leading to increases in
[Ca2+]i
(31). It has been shown that, in the heart,
Ca2+-inhibitable AC is present
(16, 18, 19, 42), while both Ca2+/calmodulin-activated AC and
the Ca2+/calmodulin-insensitive AC
are not detectable (16). Moreover, cardiac cAMP production is inhibited
by Ca2+ (6, 8, 28, 34). The
observations suggest the possibility of an inhibitory action of the
phosphoinositol/Ca2+ pathway on
the AC/cAMP pathway via an increase in
[Ca2+]i
in the cardiac
-opioid receptor. To address this question, we first
determined the effects of U-50488 and intracellular
Ca2+ on cAMP accumulation induced
by forskolin in the rat ventricular myocyte. Second, we studied the
effects of the
-agonist on cAMP accumulation after interference with
the phosphoinositol/Ca2+ pathway.
The results indicate that activation of the
phosphoinositol/Ca2+ pathway by
-receptor stimulation with U-50488 leads to inhibition of cAMP in
the heart.
 |
MATERIALS AND METHODS |
Measurement of
[Ca2+]i.
Ventricular myocytes were isolated from the heart of male
Sprague-Dawley rats (190-210 g) using a collagenase perfusion
method described previously (10). Immediately after decapitation, the heart was rapidly removed from the rat and perfused in a retrograde manner at a constant flow rate (10 ml/min) with oxygenated Joklik modified Eagle's medium supplemented with 1.25 mM
CaCl2 and 10 mM
N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic
acid, pH 7.2, at 37°C for 5 min followed by 5 min in the same
medium without Ca2+. Type I
collagenase was added to the medium to a concentration of 125 U/ml with
0.1% (wt/vol) bovine serum albumin (BSA). After 35-45 min of
perfusion with medium containing collagenase, the atria were discarded,
and the ventricular tissue was dissociated by shaking in the same
oxygenated collagenase solution for 5 min at 37°C. The ventricular
tissue was cut into small pieces with a pair of scissors followed by
stirring with a glass rod for 5 min, which separated the ventricular
myocytes from each other. The residue was filtered through 250-µm
mesh screens, sedimented by centrifugation at 100 g for 1 min, and resuspended in fresh Joklik solution with 2% BSA. More than 80% of the cells were rod shaped and not trypan blue permeable.
Ca2+ concentration of the Joklik
solution was increased gradually to 1.25 mM in 30 min.
Ventricular myocytes were incubated with fura 2-AM (4 µM) in Joklik
solution supplemented with 1.25 mM
CaCl2 for 25 min. The unincorporated dye was removed by washing the cells two times in fresh
incubation solution. The loaded cells were kept at room temperature
(24-26°C) for 30 min before measurement of
[Ca2+]i
to allow the fura 2-AM in the cytosol to de-esterify.
The ventricular myocytes loaded with fura 2-AM were transferred to the
stage of an inverted microscope (Nikon) in a superfusion chamber at
room temperature. The inverted microscope was coupled with a
dual-wavelength excitation spectrofluorometer (Photo Technical International). Myocytes were perfused with Krebs bicarbonate buffer
containing (in mM) 118 NaCl, 5 KCl, 1.2 MgSO4, 1.2 KH2PO4, 25 NaHCO3, and 11 glucose, with
1% dialyzed BSA and a gas phase of 95%
O2-5%
CO2. Fluorescent signals obtained
at 340 nm (F340) and at 380 nm
(F380) excitation wavelength
were stored in a computer for data processing and analysis. The
F340-to-F380
ratio was used to represent
[Ca2+]i
changes in the myocyte.
For
[Ca2+]i,
U-50488 at 3 × 10
5 M
was used based on previous studies. U-50488 at this concentration
significantly increased
[Ca2+]i,
which was blocked by specific
-antagonists (31, 35, 37). The
concentrations of A-23187 (26) and U-73122 (17, 32) used in the present
study were based on previous studies. Forskolin at 10 µM was chosen
based on previous studies that used forskolin at 1-100 µM for
similar purposes (14, 29, 36). More importantly, we found that,
although U-50488 inhibited the effects of forskolin at 1-10 µM
significantly, the inhibitory effect of the
-agonist was much more
obvious when forskolin at 10 µM was used (Fig.
1A).

View larger version (15K):
[in this window]
[in a new window]

View larger version (18K):
[in this window]
[in a new window]
|
Fig. 1.
Inhibitory effects of U-50488 on forskolin-induced cAMP accumulation in
rat myocytes. A: effects of U-50488 at
30 µM on cAMP-accumulation induced by forskolin at 1-10 µM. ,
Control group; , forskolin only; , forskolin in the presence of
U-50488; n = 8-16.
B: dose-related inhibition by U-50488
on cAMP accumulation induced by forskolin at 10 µM;
n = 6. Values are means ± SE. # and ## Significantly different from control (no forskolin) at
P < 0.05 and
P < 0.01, respectively. *
and ** Significantly different from the corresponding groups with
forskolin only at P < 0.05 and
P < 0.01, respectively.
|
|
Assay of cAMP. Samples containing 3 × 106 to 6 × 106 freshly isolated ventricular
myocytes after Ca2+ loading were
incubated in an atmosphere of 5%
CO2-95% air for 2 h. U-50488 and
forskolin were added and incubated for 15 min. U-73122 and U-73433
(10
5 M) were added 5 min
before U-50488 and forskolin. At the end of treatment, the cells were
centrifuged for 5 s at 100 g. The medium was aspirated, the sediment was resuspended in the ice-cold Krebs solution and then centrifuged again for 5 s at 100 g, and the supernatant was aspirated.
Ice-cold ethanol-HCl (1 ml) was added, mixed, and left to stand for 5 min at room temperature. The supernatant was centrifuged at 3,000 g for 5 min and collected with a
pipette. The precipitate was washed with 1 ml of ethanol-water (2:1),
mixed, and centrifuged at 3,000 g for
5 min. The supernatant was combined to evaporate to dryness at 55°C
under a stream of nitrogen. The sediment was stored at
20°C
for assay of cAMP. The pellets were neutralized in 0.1 N NaOH for
protein determination with the method of Lowry et al. (23), using BSA
as a standard.
The determination of cAMP utilized a competitive binding assay with a
kit from Amersham. Briefly, 50 µl of 0.5 M
tris(hydroxymethyl)aminomethane (4 mM EDTA) were added to 50 µl of
each sample on ice, followed by 50 µl of
[3H]cAMP and 100 µl
of binding protein. The samples were vortexed for 5 s, placed in an ice
bath, and allowed to incubate for 2 h. Charcoal suspension (100 µl)
was added, and the samples were vortexed for 10 s and centrifuged at
12,000 g for 2 min at 4°C. Samples
of 200 µl of supernatant were removed for scintillation counting.
To observe the effect of
[Ca2+]i
on the action of U-50488, the cell-permeant
Ca2+ chelator BAPTA-AM (25 µM)
was added for 30 min to chelate intracellular Ca2+ (22), and the
Ca2+ ionophore A-23187 was added
for 5 min before the administration of the
-agonist.
Drugs and chemicals. The substances
A-23187, U-50488, fura 2-AM, type I collagenase, neomycin, forskolin,
and pertussis toxin (PTX) were purchased from Sigma Chemical.
Norbinaltorphimine (Nor-BNI) was from Tocris Cookson. U-73122 and
U-73433 were from Research Biochemicals International. The
[3H]cAMP assay system
was from Amersham International. Fura 2-AM, forskolin, A-23187,
U-73122, and U-73433 were dissolved in dimethyl sulfoxide (DMSO), and
other chemicals were dissolved in distilled water. The final
concentration of DMSO was 0.1%, and at this concentration DMSO had no
effect on either
[Ca2+]i
or cAMP.
Statistical analysis. Data are
expressed as means ± SE. For analysis of the differences between
means, unpaired Student's t-test was
used with the exception of experiments involving the measurement of
[Ca2+]i
in which the paired Student's t-test
was used.
 |
RESULTS |
Effects of U-50488 on
[Ca2+]i
and forskolin-induced accumulation of intracellular cAMP in the rat
ventricular myocyte.
In agreement with the well-documented observations, forskolin
(1-10 µM) dose dependently increased the cAMP content (Fig. 1A). The effects of forskolin were
significantly attenuated by U-50488 at 3 × 10
5 M (Fig.
1A). We used forskolin at 10 µM
in the following experiments in view of the obvious inhibitory effect
of U-50488.
At 10
6 to 5 × 10
5 M, U-50488
dose dependently and significantly inhibited the forskolin-induced
accumulation of cAMP (Fig. 1B). At
30 µM, U-50488 also induced an elevation of
[Ca2+]i
in the quiescent single ventricular myocyte (see Fig. 5,
A and
B), in agreement with previous
observations (31, 35, 37). The effects of U-50488 at 30 µM on cAMP
(Fig. 2) and
[Ca2+]i
(data not shown) were reversed by Nor-BNI (5 µM) and preincubation with 200 ng/ml PTX for 6 h (Fig. 2).

View larger version (20K):
[in this window]
[in a new window]
|
Fig. 2.
Effects of pretreatment with pertussis toxin (PTX, 200 ng/ml) for 6 h
or norbinaltorphimine (Nor-BNI, 5 µM) for 5 min on inhibitory effect
of U-50488 (30 µM; filled bars) on forskolin-induced intracellular
cAMP accumulation. Open bars, no U-50488. Values are means ± SE;
n = 6. ** Significantly
different from control at P < 0.01.
|
|
Effects of A-23187, a
Ca2+ ionophore,
on
[Ca2+]i
and forskolin-induced accumulation of intracellular cAMP in the rat
ventricular myocyte.
To determine the effect of an artificial increase in
[Ca2+]i
on cAMP accumulation, we made use of a
Ca2+ ionophore, A-23187, which
produced a dose-dependent increase in
[Ca2+]i
(Fig. 3, A
and B). It also decreased the
forskolin-induced accumulation of cAMP (Fig.
3B). The effects of A-23187 on both [Ca2+]i
and cAMP accumulation were attenuated when the myocytes were incubated
in a Ca2+-free medium but not by
preincubation with PTX (200 ng/ml) for 6 h (Fig.
4).

View larger version (30K):
[in this window]
[in a new window]

View larger version (17K):
[in this window]
[in a new window]
|
Fig. 3.
Effects of A-23187, Ca2+
ionophore, on intracellular Ca2+
concentration
([Ca2+]i)
and intracellular cAMP accumulation in rat ventricular myocytes.
A: representative tracings showing
effects of A-23187 on
[Ca2+]i
in single ventricular myocytes. B:
relationship between
[Ca2+]i
in single ventricular myocytes ( , n = 6) and intracellular cAMP in ventricular myocytes ( ,
n = 6) in response to A-23187.
|
|

View larger version (20K):
[in this window]
[in a new window]
|
Fig. 4.
Effects of free extracellular Ca2+
plus ethylene glycol-bis( -aminoethyl
ether)-N,N,N',N'-tetraacetic
acid (EGTA, 1 mM) and pretreatment with PTX (200 ng/ml) for 6 h on
inhibitory effect of A-23187 on intracellular cAMP accumulation. Solid
and open bars, presence or absence of A-23187, respectively. Values are
means ± SE; n = 6. ** Significantly different from control at
P < 0.01.
|
|
Effects of U-50488 on
[Ca2+]i
and forskolin-induced accumulation of intracellular cAMP in the rat
ventricular myocyte after prior administration of BAPTA-AM, an
intracellular
Ca2+ chelator.
Figure 5 showed that 25 µM BAPTA-AM
reduced the basal
[Ca2+]i
level in the single ventricular myocyte and increased forskolin-induced accumulation of cAMP. When administered 30 min before U-50488, it
completely abolished the effects of U-50488 on
[Ca2+]i
and forskolin-induced accumulation of intracellular cAMP in the rat
ventricular myocyte.

View larger version (21K):
[in this window]
[in a new window]
|
Fig. 5.
Effects of
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic
acid-acetoxymethyl ester (BAPTA-AM, 25 µM), a
Ca2+ chelator, for 30 min on
U-50488-induced elevation of
[Ca2+]i
(A: representative tracings;
B: effect at 30 min after
pretreatment) and attenuation of forskolin-induced cAMP accumulation
(C: effect at 30 min after
pretreatment) in quiescent ventricular myocytes. Solid and open bars,
presence or absence of U-50488, respectively. Values are means ± SE;
n = 6. ** Significantly
different from corresponding control at
P < 0.01. # Significantly different from group with forskolin only at
P < 0.05.
|
|
Effects of U-50488 on
[Ca2+]i
and forskolin-induced accumulation of intracellular cAMP in the rat
ventricular myocyte after prior administration of U-73122 and neomycin,
specific inhibitors of PLC.
In agreement with the previous observations (17, 32), U-73122 (but not
its structural isomer U-73433) at
10
5 M and neomycin at 1 mM
completely blocked the effect of U-50488 on
[Ca2+]i
(Fig. 6, A
and B). These two agents also
significantly attenuated the suppressive effect of U-50488 on
forskolin-induced accumulation of cAMP in the ventricular myocyte (Fig.
6C).

View larger version (28K):
[in this window]
[in a new window]
|
Fig. 6.
Effects of U-73122, U-73433, and neomycin on U-50488-induced elevation
of
[Ca2+]i
in quiescent ventricular myocytes (A:
representative tracings of the effect of pretreatment with U-73122,
U-73433, and neomycin on U-50488-induced elevation of
[Ca2+]i
in the single quiescent ventricular myocyte;
B: change in fluorescence ratio) and
effects on U-50488-induced attenuation of forskolin (10 µM)-induced
cAMP accumulation (C). Solid and
open bars, presence or absence of U-50488, respectively. Values are
means ± SE; n = 6. ** Significantly different from control at
P < 0.01.
|
|
 |
DISCUSSION |
In the present study, we found that
-opioid receptor stimulation
with the
-receptor agonist U-50488 dose dependently suppressed forskolin-induced accumulation of cAMP in the rat ventricular myocyte,
in agreement with the well-documented observations in neural tissues
(1, 20) and in the heart (41). The effect was mediated by a
PTX-sensitive G protein. We also observed that
-receptor stimulation
activated the phosphoinositol/Ca2+
pathway, which involves a PTX-sensitive G protein, consistent with
previous observations (17, 31, 32, 37).
The effect of U-50488 on cAMP was similar to that of the
Ca2+ ionophore, which increased
[Ca2+]i,
but opposite to that of BAPTA-AM, a
Ca2+ chelator, which reduced
[Ca2+]i.
We also observed that abolition of the U-50488-induced elevation of
[Ca2+]i
with BAPTA-AM also abolished the U-50488-induced suppression of cAMP
accumulation induced by forskolin. In addition, inhibition of PLC with
specific inhibitors U-73122 (not its structural isomer) and neomycin
not only abolished the elevation in
[Ca2+]i
but suppressed cAMP accumulation in response to
-receptor stimulation. The observations suggest that activation of the
phosphoinositol/Ca2+ pathway may
suppress the AC/cAMP pathway. An elevation of
[Ca2+]i,
which is secondary to the activation of PLC and
IP3 upon
-receptor stimulation,
is the most likely mediator of the suppressive action of the
phosphoinositol/Ca2+ pathway on
the AC/cAMP pathway. Circumstantial evidence also suggests a similar
cross talk between the two signal transduction pathways in bradykinin
(4), substance K (9), and
1-adrenergic (5) and muscarinic
(12) receptors. The importance of
Ca2+ in attenuation of cAMP
accumulation has also been observed in
-receptor in the spinal cord
(1) and
-receptor in NCB-20 cells (4).
Although the present study did not explore the site(s) of action of
Ca2+ leading to suppression of
cAMP accumulation, available evidence suggests that
Ca2+ inhibition on cAMP may result
from a direct action on the AC catalytic subunit in the heart. The
evidence is as follows. 1) Two major
forms of adenylyl cyclase expressed in the heart (types V and VI
adenylyl cyclases) are Ca2+
inhibitable (16, 19, 42). 2) The
Ca2+/calmodulin-sensitive adenylyl
cyclase and
Ca2+/calmodulin-insensitive
adenylyl cyclase are not detectable in the heart (16, 30).
3) The
Ca2+/calmodulin-stimulated
phosphodiesterase (PDE) is not present in the heart (3, 38).
4)
Ca2+ inhibits the cardiac cAMP
accumulation in the heart (6, 8, 28, 34).
5)
Ca2+ directly inhibits the AC
catalytic subunit in the heart (7). Further study is needed for
verification.
It is of interest to note that a relatively large change in
[Ca2+]i
induced by the Ca2+ ionophore was
needed to cause a significant suppression of cAMP production, whereas a
small increase in
[Ca2+]i
induced by U-50488 was accompanied by an obvious suppression of cAMP
accumulation. The discrepancy suggests that
[Ca2+]i
is probably not the only factor that is responsible for the suppression
of cAMP production. It has been shown that activation of protein kinase
C (PKC), secondary to the activation of the phosphoinositol pathway,
causes a reduction in the receptor-mediated intracellular cAMP increase
in rat ventricular myocytes (43) and in NCB-20 cells (15). Further
study is needed to determine if PKC is also involved in mediating the
suppressive action of the
phosphoinositol/Ca2+ pathway on
the AC/cAMP pathway upon
-receptor stimulation.
That U-50488 at the dose range of
10
6 to 5 × 10
5 M
suppressed cAMP production and elevated
[Ca2+]i
via the phosphoinositol/Ca2+
pathway is in contrast to the obvervation in the cultured embryonic rat
heart myoblast that U-50488 at nanomolar concentrations inhibits cAMP
without elevating [Ca2+]i, whereas, at
micromolar concentrations, it elevates
[Ca2+]i
and supresses cAMP (21). The signal tranduction processes in the
-receptor of different tissues may be different. Further study is
needed for verification.
A major concern of the findings is the physiological significance of
the effects of
-receptor stimulation with high concentrations of
U-50488, which is in the order of
10
5 M. Previous studies
showed that, in whole animal or isolated perfused heart preparations,
myocardial ischemia-reperfusion induces cardiac arrhythmias, which
could be reversed by
-receptor antagonist, MR-2266 (33, 39), and
Nor-BNI (24). The observation suggests that, during myocardial
ischemia-reperfusion, there may be an increased release of endogenous
-agonists from the heart. The endogenous
-opioids may reduce the
cardiac contractility, a well-established action of
-opioid (40),
most likely via suppressing cAMP and/or depleting
Ca2+ from its intracellular store.
The effect protects the heart as oxygen consumption is reduced.
Therefore, in myocardial ischemia-reperfusion, a high concentration of
the
-opioid is probably secreted for cardiac protection. The
occurrence of arrhythmias, an undesirable effect, may be due to
excessive release of
-agonist during myocardial ischemia-reperfusion.
In conclusion, the present study has provided for the first time
several lines of evidence indicating that activation of the phosphoinositol/Ca2+ pathway
suppresses the AC/cAMP pathway via
[Ca2+]i
upon
-receptor stimulation with U-50488 in the heart.
Further studies are needed to determine
1) whether PKC is also involved and
2) site(s) of action of
Ca2+ that result in suppression of
cAMP accumulation. The possibility of a feedback from cAMP on the
phosphoinositol/Ca2+ pathway also
warrants further study.
 |
ACKNOWLEDGEMENTS |
We thank Dr. N. S. Wong for helpful comments and C. P. Mok for
technical assistance.
 |
FOOTNOTES |
This study was supported by grants from the Research Grant Council,
Hong Kong and The University of Hong Kong.
Address for reprint requests: T. M. Wong. Dept. of Physiology, Faculty
of Medicine, The Univ. of Hong Kong, Li Shu Fan Bldg., Sassoon Road,
Hong Kong.
Received 18 March 1997; accepted in final form 12 September 1997.
 |
REFERENCES |
1.
Attali, B.,
D. Saya,
and
Z. Vogel.
-Opioid agonists inhibit adenylate cyclase and produce heterologous desensitization in rat spinal cord.
J. Neurochem.
52:
360-369,
1989[Medline].
2.
Bakalyar, H. A.,
and
R. R. Reed.
Identification of a specialized adenylyl cyclase that may mediate odorant detection.
Science
250:
1403-1406,
1990[Medline].
3.
Bode, D. C.,
J. R. Kanter,
and
L. L. Brunton.
Cellular distribution of phosphodiesterase isoforms in rat cardiac tissue.
Circ. Res.
68:
1070-1079,
1991[Abstract].
4.
Boyajian, C. L.,
A. Garritsen,
and
D. M. F. Cooper.
Bradykinin stimulates Ca2+ mobilization in NCB-20 cells leading to direct inhibition of adenylylcyclase: a novel mechanism for inhibition of cAMP production.
J. Biol. Chem.
266:
4995-5003,
1991[Abstract/Free Full Text].
5.
Buxton, I. L. O.,
and
L. L. Brunton.
Action of the cardiac
1-adrenergic receptor: activation of cyclic AMP degradation.
J. Biol. Chem.
26:
6733-6737,
1985.
6.
Colvin, R. A.,
J. A. Oibo,
and
R. A. Allen.
Calcium inhibition of cardiac adenylyl cyclase. Evidence for two distinct sites of inhibition.
Cell Calcium
12:
19-27,
1991[Medline].
7.
Cooper, D. M. F.
Inhibition of adenylate cyclase by Ca2+
a counterpart to stimulation by Ca2+/calmodulin.
Biochem. J.
278:
903-904,
1991[Medline].
8.
Cros, G.,
A. Molla,
and
S. Katz.
Does calmodulin play a role in the regulation of cardiac sarcolemmal adenylate cyclase activity.
Cell Calcium
5:
365-375,
1984[Medline].
9.
DeBernardi, M. A.,
T. Seki,
and
G. Brooker.
Inhibition of cAMP accumulation by intracellular calcium mobilization in C6-2B cells stably transfected with substance K receptor cDNA.
Proc. Natl. Acad. Sci. USA
88:
9257-9261,
1991[Abstract].
10.
Dong, H.,
J. Z Sheng,
C. M. Lee,
and
T. M. Wong.
Calcium antagonistic and antiarrhythmic actions of CPU-23, a substituted tetrahydroisoquinoline.
Br. J. Pharmacol.
109:
113-119,
1993[Medline].
11.
Garritsen, A.,
Z. Yingxin,
A. F. Jordan,
D. B. Michael,
and
D. M. F. Cooper.
Inhibition of cyclic AMP accumulation in intact NCB-20 cells as a direct result of elevation of cytosolic Ca2+.
J. Neurochem.
59:
1630-1639,
1992[Medline].
12.
Goureau, O.,
Z. Tanfin,
and
S. Harson.
Prostaglandins and muscarinic agonists induce cyclic AMP attenuation by two distinct mechanisms in the pregnant-rat myometrium: interaction between cyclic AMP and Ca2+ signals.
Biochem. J.
271:
667-673,
1990[Medline].
13.
Hilal-Dandan, R.,
K. Urasawa,
and
L. L. Brunton.
Endothelin inhibits adenylate cyclase and stimulates phosphoinositide hydrolysis in adult cardiac myocytes.
J. Biol. Chem.
267:
10620-10624,
1992[Abstract/Free Full Text].
14.
Hohl, C. M.,
W. Stephan,
R. H. Fertel,
D. K. Wimsatt,
G. P. Brierley,
and
R. A. Altschuld.
Hyperthyroid adult rat cardiomyocytes. I. nucleotide content,
- and
-adrenoreceptors, and cAMP production.
Am. J. Physiol.
257 (Cell Physiol. 26):
C948-C956,
1989[Abstract/Free Full Text].
15.
Hollingsworth, E. B,
and
J. W. Daly.
Inhibition of receptor-mediated stimulation of cyclic AMP accumulation in neuroblastoma-hybrid NCB-20 cells by a phorbol ester.
Biochim. Biophys. Acta
930:
272-278,
1987[Medline].
16.
Ishikawa, Y.,
S. Katsushika,
L. Chen,
N. J. Halnon,
J. Kawabe,
and
C. J. Homcy.
Isolation and characterization of a novel cardiac adenylylcyclase cDNA.
J. Biol. Chem.
267:
13553-13557,
1992[Abstract/Free Full Text].
17.
Jin, W.,
N. M. Lee,
H. H. Loh,
and
S. A Thayer.
Opioids mobilize calcium from inositol 1,4,5-trisphosphate-sensitive stores in NG108-15 cells.
J. Neurosci.
14:
1920-1929,
1994[Abstract].
18.
Katsushika, S.,
L. Chen,
J. Kawabe,
R. Nilakantan,
N. J. Halnon,
C. J. Homcy,
and
Y. Ishikawa.
Cloning and characterization of a sixth adenylyl cyclase isoform: types and constitute a subgroup within the mammalian adenylyl cyclase family.
Proc. Natl. Acad. Sci. USA
89:
8774-8778,
1992[Abstract].
19.
Krupinski, J.,
T. C. Lahman,
C. D. Frankenfield,
J. C. Zwaagstra,
and
P. Watson.
Molecular diversity in the adenylyl cyclase family: evidence for eight forms of the enzyme and cloning of type VI.
J. Biol. Chem.
267:
24858-24862,
1992[Abstract/Free Full Text].
20.
Kurose, H.,
T. Katada,
T. Amano,
and
M. Ui.
Specific uncoupling by islet-activating protein, pertussis toxin, of negative signal transduction via
-adrenergic, cholinergic and opiate receptors in neuroblastoma x glioma hybrid cells.
J. Biol. Chem.
258:
4870-4875,
1983[Abstract/Free Full Text].
21.
Lau, S. Y., T. M. Wong, and N. S. Wong. Stimulation of
-receptor in cultured cardiomyoblast
produced different combinations of intracellular signals at low and
high concentrations of specific
-agonists (Abstract).
27th Meeting of the International Narcotics Research
Conference, Long Beach, CA. 1996, p. 89.
22.
Lew, V. L.,
R. Y. Tsien,
C. Miner,
and
R. M. Bookchin.
Physiological [Ca2+]i level and pump-leak turnover in intact red cells measured using an incorporated Ca chelator.
Nature
298:
478-481,
1982[Medline].
23.
Lowry, O. H.,
N. J. Rosebrough,
A. L. Farr,
and
R. J. Randall.
Protein measurement with the Folin phenol reagent.
J. Biol. Chem.
193:
265-275,
1951[Free Full Text].
24.
McIntosh, M.,
K. Kane,
and
J. Parratt.
Effects of selective opioid receptor agonists and antagonists during myocardial ischaemia.
Eur. J. Pharmacol.
210:
37-44,
1992[Medline].
25.
Munshi, R.,
M. A. Debernardi,
and
G. Brooker.
P2U-Purinergic receptors on C6-2B rat glioma cells: modulation of cytosolic Ca2+ and cAMP levels by protein kinase C.
Mol. Pharmacol.
44:
1185-1191,
1993[Abstract].
26.
Murray, J. J.,
P. W. Reed,
and
J. G. Dobson, Jr.
Biochemical changes accompanying enhanced cardiac contractility by ionophore A-23187.
Am. J. Physiol.
249 (Heart Circ. Physiol. 18):
H1204-H1210,
1985[Medline].
27.
Neil, S. M.,
T. Lakey,
and
S. Tomlinson.
Calmodulin regulation of adenylate cyclase activity.
Cell Calcium
6:
213-226,
1985[Medline].
28.
Potter, J. D.,
M. T. Piascik,
P. L. Wisler,
S. P. Robertson,
and
C. L. Johnson.
Calcium dependent regulation of brain and cardiac muscle adenylate cyclase.
Ann. NY Acad. Sci.
356:
220-231,
1980[Abstract].
29.
Rocha-Singh, K. J.,
D. K. Hines,
N. Y. Honbo,
and
J. S. Karliner.
Concanavalin A amplifies both
-adrenergic and muscarinic cholinergic receptor-adenylate cyclase-linked pathways in cardiac myocytes.
J. Clin. Invest.
88:
760-766,
1991[Medline].
30.
Rosenberg, G. B.,
and
D. R. Storm.
Immunological distinction between calmodulin-sensitive and calmodulin-insensitive adenylate cyclase.
J. Biol. Chem.
262:
7623-7628,
1987[Abstract/Free Full Text].
31.
Sheng, J. Z.,
and
T. M. Wong.
Chronic U50,488H abolishes inositol 1,4,5-triphosphate and intracellular Ca2+ elevations evoked by
-opioid receptor in rat myocytes.
Eur. J. Pharmacol.
307:
323-329,
1996[Medline].
32.
Sheng, J. Z.,
N. S. Wong,
H. X. Wang,
and
T. M. Wong.
Pertussis toxin, but not tyrosine kinase inhibitors abolishes effects of U-50,488H on cytosolic Ca2+ in myocytes.
Am. J. Physiol.
272 (Cell Physiol. 41):
C560-C564,
1997[Abstract/Free Full Text].
33.
Sitsapesan, R.,
and
J. R. Parratt.
The effects of drugs interacting with opioid receptors on the early ventricular arrhythmias arising from myocardial ischaemia.
Br. J. Pharmacol.
97:
795-800,
1989[Abstract].
34.
Tada, M.,
M. A. Kirchberger,
J. M. Iorio,
and
A. M. Katz.
Control of cardiac sarcolemmal adenylate cyclase and sodium, potassium-activated adenosine triphosphatase activities.
Circ. Res.
36:
8-17,
1975[Abstract].
35.
Tai, K. K.,
C. F. Bian,
and
T. M. Wong.
-Opioid receptor stimulation increase intracellular free calcium in isolated rat ventricular myocytes.
Life Sci.
51:
909-913,
1992[Medline].
36.
Taouis, M.,
R. S. Sheldon,
R. J. Hill,
and
H. J. Duff.
Cyclic AMP-dependent regulation of the number of [3H]batrachotoxinin benzoate binding sites on rat cardiac myocytes.
J. Biol. Chem.
266:
10300-10304,
1991[Abstract/Free Full Text].
37.
Ventura, C.,
H. Spurgeon,
E. G. Lakatta,
C. Guarnieri,
and
M. C. Capogrossi.
and
Opioid receptor stimulation affects cardiac myocyte function and Ca2+ release from an intracellular poll in myocytes and neurons.
Circ. Res.
70:
66-81,
1992[Abstract].
38.
Weishaar, R. E.,
D. C. Kobylarz-Singer,
and
H. R. Kaplan.
Subclasses of cyclic AMP phosphodiesterase in cardiac muscle.
J. Mol. Cell. Cardiol.
19:
1025-1036,
1987[Medline].
39.
Wong, T. M.,
A. Y. S. Lee,
and
K. K. Tai.
Effects of drugs interacting with opioid receptors during normal perfusion or ischaemia and reperfusion in the isolated rat heart
an attempt to identify cardiac opioid receptor subtype(s) involved in arrhythmogenesis.
J. Mol. Cell. Cardiol.
22:
1167-1175,
1990[Medline].
40.
Xia, Q.,
J. Z. Sheng,
K. K. Tai,
and
T. M. Wong.
Effects of chronic U50,488H treatment on binding and mechanical responses of the rat hearts.
J. Pharmacol. Exp. Ther.
268:
930-934,
1994[Abstract].
41.
Yamada, K.,
S. Yoshida,
and
Y. Shimada.
Atrial natriuretic polypeptide secretion via selective activation of
-opioid receptor: role of dynorphin.
Am. J. Physiol.
261 (Endocrinol. Metab. 24):
E293-E297,
1991[Abstract/Free Full Text].
42.
Yoshimura, M.,
and
D. M. F. Cooper.
Cloning and expression of a Ca2+-inhibitable adenylyl cyclase from NCB-20 cells.
Proc. Natl. Acad. Sci. USA
89:
6716-6720,
1992[Abstract].
43.
Zheng, J.-S.,
A. Christie,
M. N. Levy,
and
A. Scarpa.
Ca2+ mobilization by extracellular ATP in rat cardiac myocytes: regulation by protein kinase C and A.
Am. J. Physiol.
263 (Cell Physiol. 32):
C933-C940,
1992[Abstract/Free Full Text].
AJP Cell Physiol 274(1):C82-C87
0363-6143/98 $5.00
Copyright © 1998 the American Physiological Society