The suppressive effects of zacopride pretreatment or post-treatment on acute ischemic arrhythmias in anesthetized rats <i>in vivo</i> (mean ± SEM).

<p>The suppressive effects of zacopride pretreatment or post-treatment on acute ischemic arrhythmias in anesthetized rats <i>in vivo</i> (mean ± SEM).</p

Zacopride did not affect hypoxia-induced and glibenclamide-sensitive currents in isolated rat ventricular myocytes.

<p>(A) The I-V curves of the measured currents. a, baseline. b, hypoxia. c, 10 μmol/L glibenclamide. (B) Time course of the membrane currents measured at 20 mV under hypoxic condition. One μmol/L zacopride and 10 μmol/L glibenclamide were applied in succession.</p

The <i>I</i>_K1/Kir2.1 channel agonist zacopride prevents and cures acute ischemic arrhythmias in the rat

<div><p>Arrhythmogenesis in acute myocardial infarction (MI) is associated with depolarization of resting membraine potential (RMP) and decrease of inward rectifier potassium current (<i>I</i>_K1) in cardiomyocytes. However, clinical anti-arrhythmic agents that primarily act on RMP by enhancing the <i>I</i>_K1 channel are not currently available. We hypothesized that zacopride, a selective and moderate agonist of the <i>I</i>_K1/Kir2.1 channels, prevents and cures acute ischemic arrhythmias. To test this viewpoint, adult Sprague-Dawley (SD) rats were subjected to MI by ligating the left main coronary artery. The antiarrhythmic effects of zacopride (<i>i</i>.<i>v</i>. infusion) were observed in the settings of pre-treatment (zacopride given 3 min prior to coronary occlusion), post-treatment (zacopride given 3 min after coronary occlusion) and therapeutic treatment (zacopride given 30 s after the onset of the first sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) post MI). In all the three treatment modes, zacopride (15 μg/kg) inhibited MI-induced ventricular tachyarrhythmias, as shown by significant decreases in the premature ventricular contraction (PVC) and the duration and incidence of VT or VF. In Langendorff perfused rat hearts, the antiarrhythmic effect of 1 μmol/L zacopride were reversed by 1 μmol/L BaCl₂, a blocker of <i>I</i>_K1 channel. Patch clamp results in freshly isolated rat ventricular myocytes indicated that zacopride activated the <i>I</i>_K1 channel and thereby reversed hypoxia-induced RMP depolarization and action potential duration (APD) prolongation. In addition, zacopride (1 μmol/L) suppressed hypoxia- or isoproterenol- induced delayed afterdepolarizations (DADs). In Kir2.x transfected Chinese hamster ovary (CHO) cells, zacopride activated the Kir2.1 homomeric channel but not the Kir2.2 or Kir2.3 channels. These results support our hypothesis that moderately enhancing <i>I</i>_K1/Kir2.1 currents as by zacopride rescues ischemia- and hypoxia- induced RMP depolarization, and thereby prevents and cures acute ischemic arrhythmias. This study brings a new viewpoint to antiarrhythmic theories and provides a promising target for the treatment of acute ischemic arrhythmias.</p></div

The preventative and curative effects of zacopride on MI- induced ventricular arrhythmias in anesthetized rats <i>in vivo</i>.

<p>(A) Representative condensed ECGs (25 s/div). I, pretreatment; II, post-treatment; III, therapeutic treatment. (B) Time course of ECG traces for saline control rats (coronary occlusion + saline <i>i</i>.<i>v</i>.). Zac, zacopride, at 15 μg/kg. Lidoc, lidocaine, at 7.5 mg/kg.</p

Representative transmembrane potentials (TMPs) showing the effects of zacopride on the RMP (A) and AP (B) in rat ventricular myocytes under hypoxic conditions.

<p>The right panel of B shows the statistical analysis of APD changes in response to zacopride (1 μmol/L) or zacopride (1 μmol/L) plus BaCl₂ (1 μmol/L). Zac, zacopride. h, hypoxia. N = 6. ** <i>P</i> < 0.01, <i>vs</i>. normoxia. ^# <i>P</i> < 0.05, ^## <i>P</i> < 0.01, <i>vs</i>. Zac.</p

Effects of zacopride on ischemia-induced ventricular tachyarrhythmias in the <i>ex vivo</i> rat hearts.

<p>Zacopride at 1 μmol/L decreased the total number of PVC episodes (A), the mean episode duration of VT (B) or VF (C), and the incidence of VT or VF (D). BaCl₂ at 1 μmol/L partially reversed the effect of zacopride. Zac, zacopride. * <i>P</i> < 0.05, ** <i>P</i> < 0.01.</p

Effects of zacopride on <i>I</i>_Kir2.x currents in hypoxic CHO cells.

<p><b>(A) and (B), Kir2.1. (C) Kir2.2. (D) Kir2.3.</b> The hypoxia-induced decrease of <i>I</i>_Kir2.1 was reversed by zacopride, whereas <i>I</i>_Kir2.2 and <i>I</i>_Kir2.3 were refractory to both hypoxia and zacopride treatment. Zac, zacopride. Hyp, hypoxia. N = 6. * <i>P</i> < 0.05, ** <i>P</i> < 0.01.</p

Representative transmembrane potential (TMP) traces showing hypoxia- or Iso-induced DADs in rat ventricular myocytes.

<p>a, normoxia. b, normoxia + Zac (1 μmol/L). c, hypoxia. d, hypoxia + Zac (1 μmol/L). e, Iso (1 μmol/L). f, Iso (1 μmol/L) + Zac (1 μmol/L). Zac, zacopride. Iso, isoproterenol.</p

The effect of zacopride on the <i>I</i>_K1 of hypoxic native rat ventricular myocytes.

<p>(A) A typical recording for <i>I</i>_K1. (B) The current-voltage (I-V) curves of <i>I</i>_K1. All traces indicated Ba²⁺-sensitive currents and were normalized for cell capacitance. The inset shows an enlarged outward portion of the I-V curves. (C) The outward <i>I</i>_K1 currents (at –60 mV) decreased soon after the onset of hypoxia and were restored by zacopride. The maximal efficacy appeared at 1 μmol/L and attenuated by 1 μmol/L BaCl₂. Zac, zacopride; hyp, hypoxia. * <i>P</i> < 0.05, ** <i>P</i> < 0.01.</p