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Articles |
From the Department of Pharmacology and Therapeutics, University of Calgary (Alberta, Canada).
Abstract The role of reactive metabolites of oxygen, oxygen
radicals (O-Rs), as mediators of potentially arrhythmogenic alterations
in cellular electrical properties and contractile dysfunction of
cardiac muscle during reperfusion after ischemia was
investigated. Electrical and mechanical activities of arterially
perfused guinea pig right ventricular walls were recorded
simultaneously with intracellular microelectrodes and a force
transducer. Preparations were maintained in Krebs-Henseleit solution
(perfusion rate, 1.5 mL/min) and subjected to 30 minutes of no-flow
ischemia followed by 60 minutes of reperfusion or pretreated
with O-R scavengers (superoxide dismutase, 50 U/mL; catalase, 600 U/mL;
and mannitol, 2 mmol/L) for 10 to 20 minutes, followed by 30 minutes of
ischemia and 60 minutes of reperfusion. Reperfusion in
untreated preparations caused (1) depolarization of resting membrane
potential by 8 to 10 mV and slow recovery of action potential duration
requiring 60 minutes to attain the preischemic duration, (2)
tachyarrhythmias and premature action potentials, (3)
postischemic contractile dysfunction, and (4) increased
coronary perfusion pressure in untreated preparations. Pretreatment
with scavenger cocktail affected neither electrical nor contractile
activity before or during no-flow ischemia, but it (1)
accelerated recovery of resting membrane potential and action potential
duration, (2) reduced the incidence of tachyarrhythmia, (3) improved
contractile function, and (4) inhibited the rise in perfusion pressure
on reflow. Reperfusion with an exogenous O-Rgenerating system
containing xanthine/xanthine oxidase (X/XO, 2 mmol/L:10 mU/mL)
inhibited recovery of action potential duration and contractility.
Treatment of normoxic arterially perfused right ventricular walls with
X/XO caused a decline in action potential duration by
20% within 30
minutes. In contrast, X/XO caused a 30% increase in the duration of
action potentials in superfused papillary muscles or small strips of
right ventricular walls over the same time period. Pretreatment with
sodium nitroprusside (10 µmol/L) inhibited the decline in duration
induced by X/XO in normoxic right ventricular walls but was without
effect on prolongation due to X/XO in papillary muscles. Reperfusion
with nitroprusside after no-flow ischemia caused (1)
accelerated recovery of preischemic action potential
configuration, (2) a significant decline in the incidence of
reperfusion arrhythmias, (3) improved postischemic contractile
performance, and (4) inhibition of the increase in perfusion pressure
associated with reflow. The data indicate that slow recovery of the
action potential duration caused by O-Rs in reperfusion cannot be
explained by the direct effects of O-Rs on cardiac myocytes. Rather,
coronary vascular injury and the no-reflow phenomenon due to O-R stress
is suggested to contribute to abnormal cardiac action potential
configuration, arrhythmogenesis, and contractile dysfunction during
reperfusion after ischemia.
Key Words: ischemia/reperfusion cardiac action potential nitrovasodilator no-reflow phenomenon oxygen radicals
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