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Cardiovascular Division, Department of Medicine, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104
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ABSTRACT |
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 TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Activation of P2 purinergic
receptors exerts a potent positive inotropic effect in the cardiac
myocyte. However, it is unknown whether its activation can also cause
an increased contractility in intact heart. With the use of isolated
rat and mouse hearts, the objective of the present study was to
investigate the effect of P2 receptor agonist on the function of the
intact heart. In both Langendorff rat hearts and working rat and mouse
heart models, the P2X receptor agonist 2-methylthio-ATP (2-meSATP)
caused dose-dependent increases in left ventricular developed pressure,
rate of contraction, and rate of relaxation. The extent of P2X receptor
agonist-stimulated increase in contractility was significantly less
than that stimulated by the 
-adrenergic agonist isoproterenol.
However, the increase in contractility occurred without a significant
effect on the basal heart rate, in contrast to that caused by
isoproterenol. In isolated rat ventricular myocytes, both ATP and the
P2X receptor agonist 2-meSATP stimulated large increases in the myocyte
contractile amplitude (107 ± 13% and 99 ± 9%,
n = 17 cells from 5 rats and n = 19 cells from 6 rats, respectively). 2-meSATP caused only a slight
increase in phospholipase C activity and could stimulate myocyte
contractility in the presence of phospholipase C inhibitor U-73122,
consistent with the role of a phospholipase C-independent P2X receptor
in mediating the positive inotropic effect of 2-meSATP. The data
provide evidence for a potentially important physiological role of the
cardiac P2X receptor and for the concept that agonist at this receptor
may be beneficial for the treatment of cardiac dysfunction.
heart; drugs; ATP; purines; inotropy
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INTRODUCTION |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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P2
PURINERGIC RECEPTOR activation exerts a number of potentially
important effects in the cardiovascular system (for reviews, see Refs.
13 and 17). In cardiac myocytes, the endogenous ligand for
the P2 receptor, ATP, stimulates a large increase in the cytosolic
calcium transient and myocyte contractile amplitude (3, 5, 6,
19). ATP can be released from platelets, endothelial cells, or
the ischemic myocardium and may augment contractile state in
both healthy and diseased hearts (3, 4, 7, 8, 14, 22).
Furthermore, ATP is released as a cotransmitter with norepinephrine
from the sympathetic nerve endings and can further enhance the
-adrenergic-stimulated cardiac contractility in an additive or even
synergistic manner (24). Although these data clearly
demonstrated a pronounced stimulatory effect of ATP and other P2
receptor agonist on the cytosolic calcium level and contractile
amplitude of cardiac myocyte, it is unknown whether activation of the
P2 receptor can actually cause an increase in the contractility of the
intact heart. The effects of P2 receptor agonist on the various
important parameters of cardiac function, such as left ventricular
developed pressures (LVDP), first derivative of rate of contraction
over time (+dP/dt), first derivative of rate of relaxation
over time (
dP/dt), and spontaneous heart rate remain to be
determined. Therefore, the purpose of the present study was to
investigate the effect of P2 receptor agonist on the cardiac function
in intact heart preparations. Both the Langendorff and the working
heart models were used. To help establish the function of P2 receptor
activation in the intact heart, cardiac effects of P2 receptor agonist
were determined in both rat and mouse hearts and were directly compared
with those of -adrenergic receptor agonist.
An additional objective was to determine the role of phospholipase C (PLC) in mediating the contractile effect of P2 receptor activation. Isolated rat cardiac ventricular myocytes, which enabled biochemical and cellular studies, were used as a model to investigate the role of PLC, similar to the studies carried out in the chick embryo ventricular myocytes (16).
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MATERIALS AND METHODS |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Methods
Measurement of cardiac functions in intact heart preparations. After intravenous injection of heparin sodium via tail vein (500 U/kg) and intraperitoneal anesthetization with Nembutal (125 mg/kg for rats and 150 mg/kg for mice), the heart, with all major vessels and lungs attached, was excised. The aorta was then cannulated with a 20-gauge catheter and was positioned ~2 mm above the coronary ostia. For the Langendorff method, a water-filled latex balloon (no. 3) was inserted into the lumen of the left ventricle via the left atrium according to a previously described method (11). The distal end of the balloon-attached catheter was connected to a pressure transducer for measurement of intraventricular pressure and ±dP/dt. The balloon was inflated to a constantly held diastolic pressure of 5-7 mmHg. The retrograde perfusion via the aorta was carried out by a perfusion pump maintaining a column of Krebs-Henseleit solution (KHS) composed of (in mM) 120 NaCl, 4.7 KCl, 2.5 CaCl2, 1.2 MgSO4, 1.2 KH2PO4, 0.5 EDTA, 25 NaHCO3, 2 pyruvate, and 11 glucose; pH 7.4 (following gassing with 95% O2-5% CO2 at 37°C) to provide a constant coronary perfusion pressure of 65 mmHg. We confirmed the coronary perfusion pressure by using a pressure transducer connected via a side port to the aorta perfusion cannula. Drugs were added in the KHS buffer and infused via retrograde perfusion of the coronary artery.
For the working heart model (10, 12), a column of KHS buffer produced a constant hydrostatic pressure of 65 mmHg (for rats) or 55 mmHg (for mice). The opening of the pulmonary vein was connected via a polyethylene (PE)-90 (for rats) or a PE-50 (for mice) catheter to a reservoir of KHS buffer that maintained a "venous return" flow into the left atrium of ~12 ml/min (rats) or 5 ml/min (mice) under the resting condition. The venous return was maintained by a constant level of hydrostatic pressure (7-8 mmHg) and yielded a steady rate of venous return. The entering KHS buffer was then switched from retrograde to antegrade perfusion and produced a work-performing heart preparation. The perfusate exited the left ventricle through the aorta cannula, which was connected to the aortic column of KHS buffer with a hydrostatic pressure of 55 mmHg (for mice) or 65 mmHg (for rat). Aortic flow was the amount of perfusate exiting the aortic cannula measured in millimeters per minute. Coronary flow, measured in millimeters per minute, was collected via opening of the pulmonary artery. The sum of aortic flow and coronary flow was the cardiac output. A 23-gauge catheter was inserted into the left ventricle, and its distal end was connected to a pressure transducer to record LV pressures and ±dP/dt. The LVDP was the difference between LV systolic and diastolic pressure. A side port of the reservoir allowed direct infusion of-adrenergic agonist isoproterenol or P2X receptor
agonist 2-methylthio-ATP (2-meSATP) into the KHS buffer that entered
the left ventricle via the left atrium, which then entered the coronary
circulation after ejection of drug-containing perfusate into the aorta.
The pressure recordings were channeled from amplifiers that had been
precalibrated by a transducer simulator/calibrator (Kent Scientific;
Litchfield, CT). The signals were then digitized via an interface board
(model PCM-DAS 16S/330, Computer Boards; Mansfield, MA), which provided
a high level of performance with analog input channels and digital
channels. Data were analyzed by computer software (WorkBench for
Windows+, Kent Scientific) designed for a personal computer (Dell). The
amplified and digitized signals from the transducers were constantly
displayed and analyzed. Data acquisition, signal display (LV pressures,
±dP/dt, and heart rate), and data analysis programs were
run concurrently from the hard drive of the computer. Data points under
each basal condition and during infusion of each drug concentration
were summarized as means ± SE. Data obtained with and without
drug were analyzed by paired Student's t-test for possible
statistically significant differences. For comparing the
effects between groups treated with two different agonists or under
different conditions, unpaired t-test was used.
Preparation of homogeneous populations of cardiac ventricular myocytes isolated from adult Sprague-Dawley rats. Cardiac ventricular myocytes were prepared according to a modification of previously described procedure (23). In brief, hearts from 250-g adult Sprague-Dawley rats were perfused in a retrograde manner through the aorta with calcium-free HEPES/KHS buffer containing (in mM) 24.8 HEPES, 118 NaCl, 4.0 KCl, 15 glucose, 1 MgSO4, and 1.2 KH2PO4, pH 7.4, as well as collagenase for 30 min at 37°C. All solutions were bubbled with 100% oxygen. Hearts were then minced into small pieces with scissors and subjected to a 10-min extraction in the HEPES/KHS buffer (containing collagenase) in a shaking water bath at 37°C. Dislodged and isolated cells were neutralized with a medium containing 10% bovine serum albumin (BSA), 20% Dulbecco's modified Eagle's medium (DMEM), and HEPES/KHS buffer (70%, by volume) with a calcium concentration of 0.36 mM. The supernatant was removed by decantation with a pipette, and the combined pellets were resuspended in fresh washing media. After the cells were allowed to settle for 10 min, the washing medium was removed. The cells were resuspended in fresh washing media and settled carefully over a BSA bed (6% BSA in DMEM), which helped eliminate round, contracted myocytes as well as endothelial and smooth muscle cells. Rod-shaped ventricular cells were allowed to settle for 10-15 min, when the BSA solution was removed completely. The final pellet was resuspended in media containing 6% fetal bovine serum in DMEM with a calcium concentration of 1.8 mM, and the cells were plated in 35-mm culture plates for contractility studies. Typical preparations yielded >80-90% rod-shaped viable ventricular myocytes.
Coating of plates with laminin. Contractility studies were performed using 12-mm glass coverslips coated with laminin (1 µg/ml) in 35-mm culture plates. Plates containing laminin-DMEM solution were stored for 24 h at 4°C. The solution was then removed, and cells were plated as described above.
Measurement of myocyte contractile amplitude.
Measurement of myocyte contractile amplitude was performed by using an
optical video system as previously described (1, 23). A
12-mm glass coverslip was placed on the stage of an inverted phase
contrast microscope in a perfusion chamber warmed up to 37°C and
superfused at a rate of 1 ml/min with HEPES-buffered solution
containing (in mM) 5 HEPES, 0.9 CaCl2, 4 KCl, 140 NaCl, 0.5 MgCl2, and 11 glucose (pH 7.4). Myocytes were field
stimulated at a rate of 2 Hz with platinum electrodes connected to a
voltage stimulator. Light-dark contrast at the edge of the myocyte
provided a marker for measurement of the amplitude of motion. The
amplitude of myocyte motion remained unchanged for at least 10 min,
indicating the stability of the preparation. Myocytes were then
perfused for 3 min with the same HEPES-buffered solution containing the P2 receptor or -adrenergic receptor agonist. Changes in contractile amplitude were monitored, and recordings were made at 1-min intervals. The contractility measurement was made on only one cell per coverslip and each plate contained three coverslips.
Measurement of phosphoinositide response. Inositol phosphates were determined according to the basic method of Berridge et al. (2) and further modified as described by Podrasky et al. (16). Cells were preincubated with 10 µCi/ml of myo-[3H]inositol for 4 h and washed with inositol-free DMEM containing 15 mM LiCl and incubated in this LiCl buffer for 10 min at 37°C before being exposed to ATP or other nucleotide analogs. After extraction with 1 ml of chloroform-methanol-HCl (at 1:2:0.5 vol/vol/vol), the various inositol phosphates were separated on a 1.0-ml anion exchange column (AG × 8 resin, formate form), and D-myo-inositol 1-phosphate [Ins(1)P], D-myo-inositol 1,4-bisphosphate [Ins(1,4)P2], and D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] were eluted sequentially with 100 mM formic acid/200 mM ammonium formate, 100 mM formic acid/600 mM ammonium formate, and 100 mM formic acid/1 M ammonium formate, respectively. Columns were calibrated with each inositol phosphate standard to confirm the complete separation of Ins(1)P, Ins(1,4)P2, and Ins(1,4,5)P3. Recovery of each inositol phosphate was >95%. In other experiments, myocytes were preincubated with 5 µCi/ml of myo-[3H]inositol for 18 h, and the effects of P2 receptor agonists were then determined.
Materials
Myo-[3H]inositol was obtained from DuPont-New England Nuclear (Boston, MA). ATP, ADP, AMP,
,-methylene ATP, ,
-methylene ATP, 2-meSATP, and
isoproterenol were obtained from Sigma (St. Louis, MO). Collagenase
(type 2) was from Worthington Biochemicals (Lakewood, NJ).
Three-month-old Sprague-Dawley rats and CD-1 mice were obtained from
Charles River (Cambridge, MA).
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RESULTS |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Effect of 2-meSATP on Cardiac Function in Langendorff and Working Rat Heart Preparations
Although activation of the P2 purinergic receptor can cause a significant stimulation of the contractile amplitude in isolated cardiac myocytes, the question arises regarding whether the receptor can also mediate an increase in the contractility of the intact heart. To study this question, the contractile effect of 2-meSATP in isolated Langendorff-perfused heart preparation was determined. The P2X receptor agonist caused a significant increase in +dP/dt anddP/dt in a dose-dependent manner (Fig.
1A). The maximal stimulation occurred at 100 nM of 2-meSATP and showed increases of 22 ± 3.5% and 17.3 ± 2.8% for +dP/dt and dP/dt,
respectively (n = 5, P < 0.05, paired
t-test). LVDP also increased significantly in the presence
of 100 nM 2-meSATP (% increase was 14.5 ± 1.6%, means ± SE, n = 5, P < 0.01, paired
t-test). There was no significant change in the heart rate
or coronary flow at any of the 2-meSATP concentrations
(P > 0.1). These data indicate that activation of the
P2X receptor can enhance cardiac performance without an attendant
increase in the heart rate in the Langendorff model. In comparison, the
maximal -adrenergic stimulated increases in LVDP, +dP/dt,
and dP/dt were 142 ± 31, 370 ± 28, and
282 ± 59%, respectively (means ± SE, n = 5, P < 0.001, and paired t-test) and were
significantly larger than the corresponding maximal increases in these
parameters by 2-meSATP (P < 0.05, t-test).
Whereas the P2X receptor agonist was able to stimulate cardiac
contractility without affecting the heart rate, isoproterenol
stimulated both the basal contractility (Fig. 1B) and heart
rate. The percent increase in heart rate stimulated by 10 nM
isoproterenol was 35 ± 4% (n = 5, P < 0.05, paired t-test).
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The effect of P2X receptor agonist was then tested in the working heart
model. 2-meSATP also caused a significant increase in +dP/dt
and dP/dt in a concentration-dependent manner with the
maximal effect occurring at 100 nM (Fig. 1A) (% stimulation was 30 ± 4 and 24.5 ± 3, n = 5, P < 0.05, paired t-test). There was no
significant stimulatory or inhibitory effect on the basal heart rate at
any of the P2X agonist concentrations.
P2X receptor agonist can stimulate contractility and enhance
performance in working mouse heart.
A working mouse heart model was also used to further confirm the
cardiac effects of P2X receptor activation in the intact heart. Similar
to the data obtained in Langendorff and working rat heart models,
2-meSATP also caused dose-dependent increases in +dP/dt and
dP/dt (maximal percent stimulation of 24.5 ± 5.5% and 19.5 ± 2%, respectively, n = 5, P < 0.05, paired t-test) without significant effect on the heart rate (Fig.
2). Similar to the result obtained in the
Langendorff model, there was no observed arrhythmia at any of the P2X
agonist concentrations in the working heart preparation. The P2
receptor agonist also caused a significant increase in the cardiac
output (Table 1).
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dP/dt were 90 ± 7% and 47 ± 4%, respectively
(n = 5, P < 0.05, paired
t-test, Fig.
3A). The
isoproterenol-stimulated increases in +dP/dt and dP/dt were significantly larger than the corresponding
increases stimulated by the maximally effective concentration of
2-meSATP (P < 0.05, t-test). The increase
in cardiac output produced by isoproterenol was also significantly
higher than that elicited by 2- meSATP (Table 1, P < 0.05, t-test). Similar to the rat heart, isoproterenol
caused a marked increase in the basal heart rate (Fig. 3C)
(P < 0.05, paired t-test).
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Activation of P2 purinergic receptor increased the contractile
amplitude of individual rat cardiac myocytes.
To confirm that the same P2 receptor agonists can stimulate the
contractility of individual isolated cardiac myocytes, effects of the
agonists on the contractile amplitude were determined in cardiac
myocytes isolated from Sprague-Dawley rats that were age and weight
matched with those used in the intact heart studies. ATP was able to
stimulate a marked increase in the myocyte contractile amplitude, with
a half-maximal effective concentration (EC50) of 0.13 ± 0.01 µM and a maximal increase of 107 ± 13%
(n = 17 cells from 5 rats with 3-4 myocytes per
animal, means ± SE, P < 0.001, paired
t-test) (Fig. 4). ADP and AMP
had little stimulatory effect on the myocyte contractility with maximal
increases of only 32 ± 8 (15 cells from 5 rats with 3 myocytes
per rat, means ± SE, P < 0.05, paired
t-test) and 18 ± 5% (n = 13 cells
from 4 rats with 3 or 4 myocytes per animal, P < 0.05, paired t-test), respectively. Among the various ATP analogs,
2-meSATP was the most potent and efficacious agonist in stimulating the
myocyte contractility with an EC50 of 0.08 ± 0.01 µM and a maximal increase of 99 ± 9% (n = 19 cells from 6 rats with 3 or 4 myocytes per animal, means ± SE,
P < 0.001, paired t-test) (Fig. 4). The P2 receptor agonist ,-methyleneATP was ineffective at stimulating myocyte contractility with a maximal increase of 19.4 ± 4.1% at 10 µM (17 cells from 5 rats with 3 or 4 cells per animal,
P < 0.05, paired t-test).
,-Methylene-ATP was less effective at stimulating myocyte
contractility with a maximal increase of <10% (n = 12 cells from 4 rats with 3 cells per animal). These data are
consistent with the hypothesis that a 2- meSATP-sensitive P2
receptor is involved in mediating the positive inotropic response to
ATP.
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-adrenergic-stimulated increase in myocyte
contractility, the positive inotropic effect of 2-meSATP was
significantly less than that induced by isoproterenol (100 nM), which
typically caused a 255 ± 37% increase in the contractile amplitude relative to unstimulated cells (n = 13 cells
from 5 rats with 2-3 myocytes per animal, P < 0.01, t-test). The maximal extent of stimulation by 2-meSATP
was ~30% of that caused by isoproterenol.
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DISCUSSION |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Previous studies (3, 5, 6, 13, 16, 19, 24) have demonstrated that ATP and ATP analogs are capable of stimulating a pronounced positive inotropic effect in isolated cardiac ventricular myocytes and in intact papillary muscle. In addition to a marked increase in the cardiac myocyte contractile amplitude, there was also a significant stimulation of the cytosolic calcium transient. Whereas these data showed a clear increase in the contractile amplitude of isolated cardiac myocyte in the presence of P2 receptor agonist, it is unknown whether the P2 receptor agonist can stimulate contractility in the intact heart.
In the present study, we investigated whether the P2 receptor
agonist-stimulated increase in the contractility of isolated cardiac
myocyte can be translated into an increase in the contractile performance of the intact heart by using both the Langendorff and the
work-performing heart models. In the Langendorff preparation, the
ability of the heart to respond to receptor agonist can be determined
by adding agonist to the buffer perfusing the heart via coronary artery
directly (10, 12). The work-performing heart model offers
several advantages that were not available in the Langendorff
model. First, the perfusing buffer was infused into the left ventricle
via the left atrium, allowing the heart to function as a pump in a more
physiological manner. Second, the coronary perfusion was performed via
a systolic-diastolic gradient more closely resembling the perfusion in
vivo. Third, the working heart was continuously loaded with constant
levels of baseline preload and afterload and allowed measurement of
cardiac output. This enabled determination of the effect of
-adrenergic or P2 receptor agonist under the same basal loading condition.
Several lines of evidence support the concept that the P2X receptor
agonist can enhance the performance of the intact heart. First, in both
the Langendorff and the work-performing rat heart models, the P2X
receptor agonist 2-meSATP stimulated significant increases in
+dP/dt and dP/dt. Second, the stimulatory
effect on cardiac function by the P2X receptor agonist is present in more than one species. Similar to the data obtained in work-performing rat heart, 2-meSATP also stimulated significant increases in
+dP/dt and dP/dt in the working mouse heart.
Third, the dose-dependent nature of the stimulatory effect and the
similarity in the maximal extent of stimulation in both Langendorff and
working heart models and in the two species argue against a nonspecific
contractile effect of the P2 agonist.
Because only low concentration of ATP was required to induce an
increase in the calcium level and myocyte contractile amplitude and
because of an apparent dose-response relationship of the ATP effect, a
cardiac myocyte P2 receptor is likely involved in mediating this
effect. Although the identity of this P2 receptor is unknown, recent
study shows that a PLC-independent mechanism appears to mediate the
positive inotropic effect of P2 receptor agonist in a cultured chick
embryo cardiac myocyte model (16). Several lines of
evidence support the conclusion that a PLC-independent pathway is also
involved in mediating the positive inotropic response to 2-meSATP in
the rat cardiac myocyte. First, 2-meSATP could induce a marked
stimulation of the myocyte contractility with very little if any effect
on the PLC activity. Second, the PLC-specific inhibitor U-73122 did not
affect the ability of 2-meSATP to stimulate myocyte contractility. The
extent of 2-meSATP-stimulated increase in contractility in the presence
of U-73122 was similar to that obtained in the absence of U-73122.
Finally, although 2-meSATP can activate multiple subtypes of the P2X
receptor, it appears to be selective at the P2X family than at the P2Y
subfamily (9, 18). In contrast to P2Y receptors, which are
coupled to PLC or adenylyl cyclase, the P2X receptors are ligand-gated
ion channels and are not coupled to PLC. Thus the inotropic effect of
2-meSATP is likely mediated via activation of a P2X receptor on the
cardiac myocyte. Taken together, the data obtained using the isolated rat cardiac myocyte are similar to those obtained in the chick embryo
cardiac myocyte and suggest that a P2X receptor is also likely involved
in mediating the positive inotropic response to 2-meSATP in the rat
heart. The positive inotropic effect of 2-meSATP was less than that
produced by the -adrenergic agonist isoproterenol. In general, the
magnitude of P2X receptor agonist-stimulated increase in contractile
amplitude was ~35-40% of that stimulated by the -adrenergic agonist.
The mechanism by which activation of the cardiac P2X receptor exerts a positive inotropic effect is unclear. The P2X receptor is a ligand-gated cation channel capable of permeating sodium and calcium when it is activated. It is possible that an influx of sodium and calcium into the cardiac myocyte leads to an increase in the sarcoplasmic reticulum content of calcium and hence a greater level of calcium transients and myocyte contractility. Further investigation is required to test this hypothesis. A potential limitation of the data obtained in the intact heart study is that 2-meSATP may be degraded by the ectonucleotidases. Although 2-thioether derivatives of adenine nucleotide are less susceptible to degradation by nucleotidases than are the unmodified adenine nucleotides (25), the extent of resistance of 2-meSATP to ectonucleotidases relative to that of ATP is modest (15). However, ATP itself was also able to stimulate a marked increase in the +dP/dt in the Langendorff rat heart preparation (a maximal increase of 28 ± 4% at 100 nM, n = 6 rats, means ± SE). Thus, even with possible degradation of ATP and 2-meSATP, the continuous perfusion of the heart with agonist-containing media likely resulted in sufficient concentration of the active agonist at or near the myocyte P2X receptor.
The maximal P2 agonist-induced increases in the +dP/dt and
dP/dt ranged from 10 to 25% of those caused by the
-adrenergic agonist. Thus activation of the P2 receptor exerts a
modest positive inotropic effect. However, the positive inotropic
effect of P2 receptor agonist was not accompanied by any significant
chronotropic effect. This is in marked contrast to the significant
positive chronotropic effect that accompanied the -adrenergic
agonist-stimulated positive inotropic effect. Thus it is possible that
the P2 receptor agonist-stimulated increase in contractility would
occur without the expense of a rate-related increase in oxygen
consumption. This property may make such agonist a beneficial agent in
the treatment of left ventricular dysfunction and heart failure.
Furthermore, an enhanced rate of relaxation by the P2X agonist suggests
that such agonist may exert a beneficial effect by improving cardiac performance with enhanced contractility and relaxation. Whether the P2
receptor-mediated positive inotropic effect also exhibits rapid
agonist-induced desensitization, like desensitization of -adrenergic
receptor by its agonist, is unclear and requires further investigation.
Future studies are needed to determine whether agonist at this P2
receptor represents a novel therapeutic target. Overall, the data
provide evidence for a potentially important physiological role of the
cardiac P2X receptor. The release of the endogenous ligand ATP may
further improve cardiac performance in healthy and/or diseased hearts.
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ACKNOWLEDGEMENTS |
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This work was supported by an American Heart Association grant-in-aid and Established Investigatorship Award and by National Heart, Lung, and Blood Institute Grant RO1-HL-48225 (to B. T. Liang).
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FOOTNOTES |
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Address for reprint requests and other correspondence: B. T. Liang, Rm. 956, BRBII/III, 421 Curie Blvd., Univ. of Pennsylvania Medical Center, Philadelphia, PA 19104 (E-mail: liangb{at}mail.med.upenn.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 6 December 2000; accepted in final form 12 March 2001.
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REFERENCES |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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