(Circulation. 1995;91:2712-2716.)
© 1995 American Heart Association, Inc.
Articles |
From the Alfred and Baker Medical Unit and Cellular Biochemistry Laboratory, Alfred Hospital and Baker Medical Research Institute, Melbourne, Australia.
Correspondence to Dr Anthony Dart, Alfred and Baker Medical Unit, Baker Medical Research Institute, Commercial Rd, Prahran (Melbourne), Victoria 3181, Australia.
| Abstract |
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Methods and Results In perfused rat hearts, ventricular tachycardia (VT), ventricular fibrillation (VF), and accumulation of Ins(1,4,5)P3 were measured during early reperfusion. A number of different compounds, including neomycin, gentamicin, streptomycin, spermine, reserpine, and prazosin, were effective in inhibiting the reperfusion-induced Ins(1,4,5)P3 release and the onset of VT and VF in parallel. A strong correlation existed between Ins(1,4,5)P3 content, measured at 2 minutes of reperfusion, and the incidence of reperfusion VT and VF. In addition, intravenous gentamicin suppressed the onset of arrhythmias under ischemic and reperfusion conditions in vivo.
Conclusions Our results are consistent with the view that Ins(1,4,5)P3 release plays a pivotal role in mediating arrhythmias during early reperfusion. Agents inhibiting Ins(1,4,5)P3 release are antiarrhythmic and may have potential use clinically.
Key Words: arrhythmia ischemia reperfusion
| Introduction |
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1-adrenoceptors was demonstrated during
postischemic reperfusion,3 and recently an
enhanced release of Ins(1,4,5)P3 was also shown to
occur.4 Oscillations of intracellular
Ca2+ are known to be arrhythmogenic.5
These findings raise the possibility that release of
Ins(1,4,5)P3 might initiate and facilitate arrhythmias and
thus that inhibition of this release might prove to be antiarrhythmic.
Aminoglycoside antibiotics and spermine were shown to inhibit
Ins(1,4,5)P3 release by binding to its precursor
phosphatidylinositol (4,5)biphosphate in many
tissues,6 7 8
and we recently reported an enhanced potency of neomycin in inhibiting
Ins(1,4,5)P3 release under conditions of
postischemia reperfusion.4 However, no studies
have tested whether other aminoglycosides have similar inhibitory
effects on Ins(1,4,5)P3 release during reperfusion or on
whether such interventions are antiarrhythmic. Thus, the present study was undertaken to examine the effects of aminoglycosides neomycin, gentamicin, streptomycin, and spermine on reperfusion-induced ventricular arrhythmias and Ins(1,4,5)P3 release in perfused rat hearts. To evaluate the potential significance of these findings, the antiarrhythmic activity of gentamicin was further investigated in intact animals.
| Methods |
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Mass Analysis of Ins(1,4,5)P3 in Isolated Perfused
Hearts
The methods used to measure the myocardial content of
Ins(1,4,5)P3 were as described previously in
detail.4 In brief, isolated hearts were perfused through
the aorta at 5
mL · g-1 · min-1 with
HEPES-buffered Krebs' medium (37°C) according to the Langendorff
procedure. The medium contained (mmol/L) Na+ 138,
K+ 5.9, Ca2+ 2.0,
Mg2+ 1.2, HCO3- 25,
PO43- 1.2, HEPES 20, and glucose 11 and was
equilibrated with 95% O2/5% CO2 (pH
7.4). Global ischemia was produced when perfusion was stopped
for 20 minutes, and reperfusion was produced when flow was reinitiated.
Propranolol (1 µmol/L), LiCl (50 mmol/L with the concentration of
Na+ reduced accordingly), and investigational agents were
added to the medium 10 minutes before ischemia and maintained
throughout the remainder of the ischemia-reperfusion
protocol.4 We ended the experiment by freezing the heart
in liquid nitrogen either immediately before reperfusion or 2 minutes
after reperfusion. A reperfusion period of 2 minutes was chosen because
our previous studies showed that the enhanced release of
Ins(1,4,5)P3 was maximal at this time.4
Ins(1,4,5)P3 was extracted in 3.5 mL of 5% trichloroacetic
acid containing 2.5 mmol/L EDTA and 5 mmol/L ATP, as previously
described in detail.4 Ins(1,4,5)P3 mass was
measured with Amersham assay kits and expressed as picomoles per
milligram of protein.4
Preparations and Protocols for Arrhythmia Experiments
Arrhythmia Experiments In Vitro
Experiments were
performed in rat hearts perfused in situ at
approximately 5
mL · g-1 · min-1 with
Krebs-Henseleit solution at 37°C.9 The perfusate
contained (mmol/L) Na+ 145, K+ 4.0,
Ca2+ 1.85, Mg2- 1.05,
HCO3- 25, PO43- 0.5,
glucose 11, and EDTA 0.027 and was constantly gassed with
O2-CO2 (95%-5%, pH 7.4). Regional
ischemia was produced by occlusion of the left coronary artery
about 3 mm from its origin with subsequent release to allow
reperfusion. The perfusion flow rate was adjusted coincidently with
coronary occlusion or reperfusion to maintain a constant perfusion
pressure. Epicardial ECG, perfusion pressure, and in some preparations,
left ventricular pressure were recorded on a Grass
polygraph.9
In all experiments, drug or vehicle infusion was started 10 minutes before coronary occlusion and then was maintained throughout the remainder of the ischemia-reperfusion protocol. A 20-minute ischemic period was used, followed by a 5-minute reperfusion period. The ECG was monitored during the ischemic period and for 5 minutes after reperfusion to ensure that the development of arrhythmias was inhibited rather than postponed by the agents tested. Ventricular arrhythmias, ie, ventricular premature beats (VPB), tachycardia (VT), and fibrillation (VF), were measured during the 5-minute reperfusion period and defined and analyzed according to the guidelines of the Lambeth Conventions.10 All experiments were performed in the presence of propranolol (1 µmol/L) and LiCl (10 mmol/L). The incidence of ischemic VT and VF was reduced significantly by treatment with propranolol to 40% and 30%, respectively, compared with 80% and 75% in control group (both P<.05) but was unaffected by LiCl (70% and 60%, respectively). The incidence of reperfusion arrhythmias was unaffected by either single agent (100% and 86% versus 67% for VT; 72% and 71% versus 67% for VF) or a combination of agents. In view of the effect of propranolol on ischemic arrhythmias, analysis was limited to reperfusion for the in vitro experiments.
Arrhythmia
Experiments In Vivo
An anesthetized, ventilated, and open-chest rat
model was used
to test the effect of gentamicin on ventricular arrhythmias during
regional ischemia and reperfusion in vivo.11 The
right carotid artery was cannulated with a Millar microtipped
transducer catheter to measure arterial blood pressure. A loose
ligature was positioned around the left coronary artery for subsequent
occlusion. The ischemic period was 10 minutes, followed by
reperfusion for 5 minutes. We found 10 minutes to be the optimal
ischemic period for the development of reperfusion arrhythmias
in this model. Gentamicin infusion, at either 2.5 or 7.5
mg · kg-1 · min-1, began 10
minutes before the onset of ischemia and continued for the
remainder of the experiment. In hearts without irreversible VF, the
coronary artery was reoccluded at the end of the experiment, and the
ischemic area was measured by a dye method and expressed as
percentages of the total ventricular weight. Arrhythmias were defined
and analyzed according to the Lambeth Conventions.10
Statistics
The
2 test with Fisher's
exact
calculation was used to estimate the significance of differences in the
incidence of VT and VF between control and drug-treated groups.
Comparison for the difference in frequencies of VPB was performed by
the Mann-Whitney test. The significance of differences for all other
comparisons was determined with paired or unpaired Student's
t test, with results presented as mean±SEM. The
least-squares method was used for linear correlation and regression
between mass content of Ins(1,4,5)P3 and incidence of
arrhythmias.
| Results |
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Reperfusion Arrhythmias in Perfused Hearts
There was no
significant difference in the incidence of
reperfusion arrhythmias between control groups from the different
experiments; therefore, combined data from 64 control rats were used.
All three aminoglycosides tested suppressed reperfusion VPB, VT, and VF
in a dose-dependent manner (Table 1
). Spermine 5 mmol/L was
also
antiarrhythmic. To further establish the role of norepinephrine and
1-adrenoceptors in mediating reperfusion arrhythmias,
other agents were tested. Interventions that depleted cardiac
norepinephrine (reserpine) or blocked
1-adrenoceptors
(prazosin) also reduced the incidence of reperfusion arrhythmias (Table
1
). On the other hand, staurosporine at a concentration known
to
be effective in inhibiting protein kinase C (PKC) in perfused rat
hearts12 did not inhibit reperfusion VT and VF, although
the frequency of VPB was reduced. This indicates that the activation of
PKC by 1,2-diacylglycerol released coincidently with
Ins(1,4,5)P313 is not important in inducing
severe reperfusion arrhythmias. All agents that inhibited
Ins(1,4,5)P3 release were also effective in suppressing
reperfusion arrhythmias. A strong correlation was observed between
tissue Ins(1,4,5)P3 levels and the incidence of VPB, VT,
and VF during reperfusion (Figure
).
|
Ischemic and Reperfusion Arrhythmias In Vivo
Coronary artery
occlusion induced high incidences of
ischemic VPB, VT, and VF in control rats that were reduced by
intravenous gentamicin in a dose-dependent manner (Table 2
).
Sustained VF occurred in 30% of control rats but in
only 10% and 0% of rats receiving gentamicin at 2.5 and 7.5
mg · kg-1 · min-1,
respectively.
|
In 13 control rats that did not have sustained VF,
reperfusion was
performed after 10 minutes of ischemia. All control rats
developed VT, and 69% developed VF during early reperfusion.
These reperfusion-mediated arrhythmias were inhibited by gentamicin at
7.5 mg · kg-1 · min-1 but not
at 2.5
mg · kg-1 · min-1 (Table
2
).
There was no significant difference between groups in the size of ischemic area as a percentage of total ventricular weight (38.1±1.5% and 38.0±3.3% versus 34.9±2.8%).
Effects of Aminoglycosides on Cardiovascular Function In Vitro and
In Vivo
In in situ perfused hearts, heart rate (HR) was unchanged by
aminoglycosides at concentrations <1 mmol/L but reduced at the high
concentration (data not shown). The pressure developed by contraction
of the left ventricle (LVDevP) did not differ between groups and was
constant during the stabilizing period (between 30 and 50 mm Hg). At
the end of the 10-minute infusion with gentamicin 1.5 mmol/L, LVDevP
was reduced to 45±7% of pretreatment values. However, LVDevP was well
maintained in hearts treated with gentamicin at two lower doses
(110±6% and 96±3% of control, respectively). Neomycin and
streptomycin produced very similar effects on LVDevP compared with
gentamicin.
In intact rats, infusion of gentamicin 7.5 mg · kg-1 · min-1 for 10 minutes reduced HR (from 429±11 to 374±14 beats per minute [bpm], P<.05) and mean arterial pressure (MAP, from 120±4 to 92±7 mm Hg, P<.05). Infusion with gentamicin 2.5 mg · kg-1 · min-1 caused only mild reductions in HR and MAP (443±6 to 428±5 bpm and 113±2 to 100±3 mm Hg, both P<.05). At the end of 10 minutes of ischemia, HR remained significantly lower in treated rats compared with untreated rats only in the high-dose group (355±12 and 422±15 versus 439±11 bpm). MAP was lower in both treated groups compared with controls (79±5 and 81±5 versus 107±6 mm Hg, both P<.05).
| Discussion |
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1-adrenoceptors.4 In the current study, the
importance of this pathway in initiating reperfusion arrhythmias was
investigated by use of agents that inhibited this pathway at various
stages. Agents that prevented release of norepinephrine or blocked
1-adrenoceptors were shown to prevent reperfusion
arrhythmias. In addition, the aminoglycosides neomycin, gentamicin,
streptomycin, and spermine, which inhibited Ins(1,4,5)P3
release, were effective antiarrhythmic agents. Such inhibitory effects
of aminoglycosides on both Ins(1,4,5)P3 release and
arrhythmias were dose dependent. Most importantly, a high degree of
correlation has been demonstrated between Ins(1,4,5)P3
release and the incidence of VPB, VT, and VF during reperfusion. The
correlation is surprisingly strong, considering the variability of
arrhythmia indexes in this model and that the two parameters were
obtained from independent experiments. Thus, these findings provide
strong evidence that the release of Ins(1,4,5)P3 is
instrumental in initiating reperfusion arrhythmias under these
conditions.
Gentamicin, the most effective agent in vitro, was also very effective
in vivo in suppressing ischemic and reperfusion arrhythmias. It
remains to be established whether the effect of gentamicin in vivo is
also due to inhibition of Ins(1,4,5)P3 release. While local
norepinephrine release and
-adrenoceptors are likely to be important
in mediating arrhythmias in
vivo,3 14 15 16 bloodborne
factors, such as neutrophils or platelet-derived
factors,17 18 are also likely to have important
influences. Thus, ischemic and reperfusion arrhythmias in vivo
may have more complex origins than those in our in vitro model.
Furthermore, the degree of ischemia in vivo may not be uniform
and thus may lead to differences in the pattern of inositol phosphate
release. Studies currently under way in our laboratory demonstrate that
while inositol phosphate content is decreased under conditions of
global and severe ischemia, the response to norepinephrine
remains intact under more moderate ischemic conditions. Thus,
it is possible that under the less-defined conditions of
ischemia in vivo, Ins(1,4,5)P3 has a role in the
development of arrhythmias during early ischemia and
reperfusion. Studies by Anyukhovsky and coworkers19 showed
a pivotal role of
1-adrenoceptors in mediating the onset
of "ischemic arrhythmias" in Purkinje fibers incubated
under conditions of simulated moderate ischemia.
The intracellular events following Ins(1,4,5)P3 release
have not been examined in this study. In normoxic cardiac tissues,
1-adrenergic stimulation has no proarrhythmic
effect.3 19
1-Agonists, however, are
arrhythmogenic in cardiac preparations exposed to ischemic (or
hypoxic) and reperfusion
conditions.3 19 20 The
electrophysiological changes induced by
1-stimulation
include potentiated abnormal automaticity, enhanced
afterdepolarizations and triggered activity, and prolonged action
potential duration, which favors reentry.21 The
intracellular events leading to these changes are most probably
increased and oscillating levels of intracellular
calcium.5 In most cell types, addition of
Ins(1,4,5)P3 causes a rapid and transient release of
Ca2+.22 The heart is relatively
insensitive to Ins(1,4,5)P3, which causes a slow
release of calcium.1 However, Ins(1,4,5)P3 was
reported to enhance calcium oscillations in myocardial
preparations.2 Furthermore, while norepinephrine
stimulation does not increase Ins(1,4,5)P3 in normoxic
hearts,23 reperfusion is associated with marked
stimulation.4 It is of interest that the sensitivity of
Ins(1,4,5)P3 receptors is enhanced under conditions of
oxidizing stress or increased intracellular
Ca2+,24 25 26 situations
pertaining
during ischemia-reperfusion.27 This raises the
possibility that in addition to enhanced Ins(1,4,5)P3
release under reperfusion conditions, the response to
Ins(1,4,5)P3 is also potentiated. These speculations remain
to be investigated.
The present study, together with other recent findings,4 provides evidence for a pivotal role of Ins(1,4,5)P3 in the genesis of reperfusion arrhythmias and perhaps of ischemic arrhythmias in vivo. These findings potentially have important clinical implications because not only catecholamines but also other factors such as thrombin, angiotensin II, endothelin, and mechanical stretch28 29 30 stimulate Ins(1,4,5)P3 formation in the heart, and many of these factors are found to be present under pathological conditions such as myocardial ischemia and reperfusion and heart failure. Agents that interfere with Ins(1,4,5)P3 release may prove to be effective clinically, constituting a new approach in antiarrhythmic drug therapy.
| Acknowledgments |
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Received February 9, 1995; revision received March 15, 1995; accepted March 27, 1995.
| References |
|---|
|
|
|---|
-Adrenergic contributions to dysrhythmia during myocardial
ischemia and reperfusion in cats. J Clin
Invest. 1980;65:161-171.
1-Receptor independent activation of protein
kinase C in acute myocardial ischemia.
Circ Res. 1992;70:1304-1312.
1-adrenergic modulation of abnormal automaticity in
`ischemic' canine Purkinje fibers.
Circ Res. 1994;74:937-944.
1-Adrenoceptors in neonatal rat cardiac myocytes:
hypoxia alters the responsiveness of
1A and
1B subtypes. Life Sci. 1993;53:411-416. This article has been cited by other articles:
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