Effects of the novel amiodarone-like compound SAR114646A on cardiac ion channels and ventricular arrhythmias in rats

Peptide Sodium Channels Modulator Mu-Agatoxin-Aa1a Prevents Ischemia-Reperfusion Injury of Cells

Ischemia-reperfusion injury (IRI) is an irreversible functional and structural injury. Restoration of normal oxygen concentration exacerbates the emergence and development of deadly cells. One of the possible moments of reperfusion damage to cells is an increase in the intracellular concentration of sodium ions. In this article, we study the mu-agatoxin-Aa1a, a modulator of sodium channels, on the processes of IRI cells damage. The toxin was synthesized using an automatic peptide synthesizer. Hypoxia was induced by reducing the content of serum and oxygen in the CHO-K1 culture. The influence of the toxin on the level of apoptosis; intracellular concentration of sodium, calcium, and potassium ions; intracellular pH; totality of reactive oxygen species (ROS), nitric oxide (NO), and ATP; and changes in the mitochondrial potential were studied. The experiments performed show that mu-agatoxin-Aa1a effectively prevents IRI of cells. Toxin reduces the level of apoptosis and prevents a decrease in the intracellular concentration of sodium and calcium ions during IRI. Mu-agatoxin-Aa1a contributes to the maintenance of elevated intracellular pH, reduces the intracellular concentration of ROS, and prevents the decrease in intracellular NO concentration and mitochondrial potential under conditions of reoxygenation/reperfusion. An analysis of experimental data shows that the mu-agatoxin-Aa1a peptide has adaptogenic properties. In the future, this peptide can be used to prevent ischemia/reperfusion tissue damage different genesis.

Effects of Modulation of Ion Channel Currents by Salidroside in H9C2 Myocardial Cells in Hypoxia and Reoxygenation

Salidroside, a phenyl-propanoid glycoside isolated from the medicinal plant Rhodiola rosea, has potent cardioprotective effects, especially against myocardial hypoxia and reoxygenation injury. However, the molecular mechanism underlying its action is still unclear. The aim of this study was to determine the effect of salidroside on sodium channel current (I_Na) and transient outward potassium channel current (I_to) in H9C2 cardiomyocytes. H9C2 cells were subcultured under anoxic conditions to mimic myocardial hypoxia and subsequently treated with salidroside. Whole cell patch clamp was performed to determine the effect of hypoxia/reoxygenation and salidroside on myocardial electrophysiological properties. In the differentiated H9C2 cells, hypoxia/reoxygenation reduced I_Na and I_to amplitude, while salidroside significantly restored both and altered the I_Na and I_to activation/inactivation kinetics in a dose-dependent manner. Our findings demonstrate that salidroside protects myocardial cells against hypoxia-reoxygenation by restoring the function of sodium and potassium channels.

Reduction in dynamin-2 is implicated in ischaemic cardiac arrhythmias

Ischaemic cardiac arrhythmias cause a large proportion of sudden cardiac deaths worldwide. The ischaemic arrhythmogenesis is primarily because of the dysfunction and adverse remodelling of sarcolemma ion channels. However, the potential regulators of sarcolemma ion channel turnover and function in ischaemic cardiac arrhythmias remains unknown. Our previous studies indicate that dynamin-2 (DNM2), a cardiac membrane-remodelling GTPase, modulates ion channels membrane trafficking in the cardiomyocytes. Here, we have found that DNM2 plays an important role in acute ischaemic arrhythmias. In rat ventricular tissues and primary cardiomyocytes subjected to acute ischaemic stress, the DNM2 protein and transcription levels were markedly down-regulated. This DNM2 reduction was coupled with severe ventricular arrhythmias. Moreover, we identified that the down-regulation of DNM2 within cardiomyocytes increases the action potential amplitude and prolongs the re-polarization duration by depressing the retrograde trafficking of Nav1.5 and Kir2.1 channels. These effects are likely to account for the DNM2 defect-induced arrhythmogenic potentials. These results suggest that DNM2, with its multi-ion channel targeting properties, could be a promising target for novel antiarrhythmic therapies.

Effects of a novel amiodarone-like compound SAR114646A on the pig atrium and susceptibility to ventricular fibrillation in dogs and pigs

Amiodarone is one of the most effective antiarrhythmic drugs. However, poor solubility of this compound has limited its intravenous application. SAR11464A is a water-soluble amiodarone-like drug that lacks iodine and inhibits multiple cardiac ion channels in vitro. This study evaluated the antiarrhythmic efficacy of this drug in vivo. In porcine studies, atrial effective refractory period (AERP) was measured in pentobarbital-anesthetized thoracotomized pigs and atrial fibrillation (AF) was induced by a premature beat. Ventricular fibrillation (VF) was induced via either burst pacing or programmed electrical stimulation (a series of progressively shorter beats, S1-S5). In canine studies, VF was induced by a 2-min occlusion of the left circumflex coronary artery during the last minute of exercise in dogs with healed myocardial infarctions (n = 8). One week later, this test was repeated after pretreatment with SAR114646A (3.0 mg/kg, i.v., slow bolus). SAR114646A produced a significant dose-dependent prolongation of AERP, inhibited AF induced by a premature stimulus, and electrically induced VF in anesthetized pigs. At 1.0 and 3.0 mg/kg, i.v., it was superior to amiodarone, dofetilide, and flecainide. In dogs, SAR114646A did not alter any ECG parameter including QTc (control, 236.9 ± 8.5 ms vs. SAR, 237.2 ± 3.5 ms) but significantly reduced the incidence of VF, protecting six of eight animals (Fisher's exact test, P = 0.01). SAR114646A was effective against both atrial and ventricular arrhythmias without altering ventricular repolarization. These data suggest that the amiodarone-like drug SAR114646A may be an effective antiarrhythmic intervention that does not adversely prolong ventricular repolarization.