Melatonin treatment improves ventricular conduction via upregulation of Nav1.5 channel proteins and sodium current in the normal rat heart

Mechanistic Insights into Melatonin's Antiarrhythmic Effects in Acute Ischemia-Reperfusion-Injured Rabbit Hearts Undergoing Therapeutic Hypothermia

The electrophysiological mechanisms underlying melatonin's actions and the electrophysiological consequences of superimposed therapeutic hypothermia (TH) in preventing cardiac ischemia-reperfusion (IR) injury-induced arrhythmias remain largely unknown. This study aimed to unveil these issues using acute IR-injured hearts. Rabbits were divided into heart failure (HF), HF+melatonin, control, and control+melatonin groups. HF was induced by rapid right ventricular pacing. Melatonin was administered orally (10 mg/kg/day) for four weeks, and IR was created by 60-min coronary artery ligation and 30-min reperfusion. The hearts were then excised and Langendorff-perfused for optical mapping studies at normothermia, followed by TH. Melatonin significantly reduced ventricular fibrillation (VF) maintenance. In failing hearts, melatonin reduced the spatially discordant alternans (SDA) inducibility mainly by modulating intracellular Ca2+ dynamics via upregulation of sarcoplasmic reticulum Ca2+-ATPase (SERCA2a) and calsequestrin 2 and attenuating the downregulation of phosphorylated phospholamban protein expression. In control hearts, melatonin improved conduction slowing and reduced dispersion of action potential duration (APDdispersion) by upregulating phosphorylated connexin 43, attenuating the downregulation of SERCA2a and phosphorylated phospholamban and attenuating the upregulation of phosphorylated Ca2+/calmodulin-dependent protein kinase II. TH significantly retarded intracellular Ca2+ decay slowed conduction, and increased APDdispersion, thereby facilitating SDA induction, which counteracted the beneficial effects of melatonin in reducing VF maintenance.

An unidentified yet notable modification on I Na and I K (DR) caused by ramelteon

Despite advancement in anti-seizure medications, 30% of patients continue to experience recurrent seizures. Previous data indicated the antiepileptic properties of melatonin and its agonists in several animal models. However, the underlying mechanisms of melatonin and its agonists on cellular excitability remain poorly understood. In this study, we demonstrated the electrophysiological changes of two main kinds of ion channels that are responsible for hyperexcitability of neurons after introduction of melatonin agonists- ramelteon (RAM). In Neuro-2a cells, the amplitude of voltage-gated Na+ (I Na) and delayed-rectifier K+ currents (I K (DR)) could be suppressed under RAM. The IC50 values of 8.7 and 2.9 μM, respectively. RAM also diminished the magnitude of window Na+ current (I Na (W)) elicited by short ascending ramp voltage, with unchanged the overall steady-state current-voltage relationship. The decaying time course of I Na during a train of depolarizing pulses arose upon the exposure to RAM. The conditioning train protocol which blocked I Na fitted the recovery time course into two exponential processes and increased the fast and slow time constant of recovery the presence of RAM. In pituitary tumor (GH3) cells, I Na amplitude was also effectively suppressed by the RAM. In addition, GH3-cells exposure to RAM decreased the firing frequency of spontaneous action potentials observed under current-clamp conditions. As a result, the RAM-mediated effect on INa was closely associated with its ability to decrease spontaneous action potentials. Collectively, we found the direct attenuation of I Na and I K (DR) caused by RAM besides the agonistic action on melatonin receptors, which could partially explain its anti-seizure activity.

Melatonin alleviates aging-related heart failure through melatonin receptor 1A/B knockout in mice

Age-related cardiovascular diseases continue to be important issues that contribute to the societal burden. Unveiling the molecular mechanisms underlying age-related cardiovascular diseases provides novel opportunities to delay aging and facilitate early disease diagnosis and treatment. This study utilized knockout mice lacking melatonin receptors type 1A (MT1) and 1B (MT2). Ultrasonography, pathological staining, and transcriptomics were used to investigate the role of MT1/2 in the hearts of aging mice. Knockout of both receptors decreased ejection fraction and exacerbated fibrosis, inflammation, oxidative stress, and apoptosis levels in aging mice. Our findings indicated that the cardiac function of MT1 knockout mice was more severely affected than that of MT2 knockout mice. Additionally, we observed that intraperitoneal administration of melatonin (20 mg/kg/day for 90 days) ameliorated abnormal cardiac function in aging mice. However, the absence of MT1/2 resulted in the inability of melatonin to improve cardiac function. Our study, utilizing an aging polymerase chain reaction assay and cell experiments, revealed that melatonin receptors potentially influence cardiac function in aging mice through their effects on leukocyte differentiation antigen 14 (CD14) expression. Consequently, melatonin receptors, particularly MT1, are key contributors to cardiac aging, and therapeutic interventions targeting this receptor are promising for delaying the progression of cardiac aging.

Blockade of Melatonin Receptors Abolishes Its Antiarrhythmic Effect and Slows Ventricular Conduction in Rat Hearts

Melatonin has been reported to cause myocardial electrophysiological changes and prevent ventricular tachycardia or fibrillation (VT/VF) in ischemia and reperfusion. We sought to identify electrophysiological targets responsible for the melatonin antiarrhythmic action and to explore whether melatonin receptor-dependent pathways or its antioxidative properties are essential for these effects. Ischemia was induced in anesthetized rats given a placebo, melatonin, and/or luzindole (MT1/MT2 melatonin receptor blocker), and epicardial mapping with reperfusion VT/VFs assessment was performed. The oxidative stress assessment and Western blotting analysis were performed in the explanted hearts. Transmembrane potentials and ionic currents were recorded in cardiomyocytes with melatonin and/or luzindole application. Melatonin reduced reperfusion VT/VF incidence associated with local activation time in logistic regression analysis. Melatonin prevented ischemia-related conduction slowing and did not change the total connexin43 (Cx43) level or oxidative stress markers, but it increased the content of a phosphorylated Cx43 variant (P-Cx43368). Luzindole abolished the melatonin antiarrhythmic effect, slowed conduction, decreased total Cx43, protein kinase Cε and P-Cx43368 levels, and the IK1 current, and caused resting membrane potential (RMP) depolarization. Neither melatonin nor luzindole modified INa current. Thus, the antiarrhythmic effect of melatonin was mediated by the receptor-dependent enhancement of impulse conduction, which was associated with Cx43 phosphorylation and maintaining the RMP level.

ECG Markers of Acute Melatonin Treatment in a Porcine Model of Acute Myocardial Ischemia

In myocardial ischemia, melatonin confers antiarrhythmic action, but its electrocardiographic expression is unclear. We aimed to evaluate the effects of melatonin treatment on electrocardiogram (ECG) parameters reflecting major arrhythmogenic factors and to test the association of these parameters with ventricular fibrillation (VF) incidence. Myocardial ischemia was induced by 40 min coronary artery occlusion in 25 anesthetized pigs. After induction of ischemia, 12 and 13 animals were given melatonin or placebo, respectively. Twelve-lead ECGs were recorded and durations of QRS, QT, Tpeak-Tend intervals and extrasystolic burden were measured at baseline and during occlusion. During ischemia, VF episodes clustered into early and delayed phases (<10 and >20 min, respectively), and QRS duration was associated with VF incidence. QT interval and extrasystolic burden did not differ between the groups. The Tpeak-Tend interval was progressively prolonged, and the prolongation was less pronounced in the treated animals. QRS duration increased, demonstrating two maxima (5−10 and 25 min, respectively). In the melatonin group, the earlier maximum was blunted, and VF development in this period was prevented. Thus, acute melatonin treatment prevented excessive prolongation of the QRS and Tpeak-Tend intervals in the porcine myocardial infarction model, and QRS duration can be used for the assessment of antiarrhythmic action of melatonin.