Protective Effect of Uridine on Structural and Functional Rearrangements in Heart Mitochondria after a High-Dose Isoprenaline Exposure Modelling Stress-Induced Cardiomyopathy in Rats.

The pyrimidine nucleoside uridine and its phosphorylated derivates have been shown to be involved in the systemic regulation of energy and redox balance and promote the regeneration of many tissues, including the myocardium, although the underlying mechanisms are not fully understood. Moreover, rearrangements in mitochondrial structure and function within cardiomyocytes are the predominant signs of myocardial injury. Accordingly, this study aimed to investigate whether uridine could alleviate acute myocardial injury induced by isoprenaline (ISO) exposure, a rat model of stress-induced cardiomyopathy, and to elucidate the mechanisms of its action related to mitochondrial dysfunction. For this purpose, a biochemical analysis of the relevant serum biomarkers and ECG monitoring were performed in combination with transmission electron microscopy and a comprehensive study of cardiac mitochondrial functions. The administration of ISO (150 mg/kg, twice with an interval of 24 h, s.c.) to rats caused myocardial degenerative changes, a sharp increase in the serum cardiospecific markers troponin I and the AST/ALT ratio, and a decline in the ATP level in the left ventricular myocardium. In parallel, alterations in the organization of sarcomeres with focal disorganization of myofibrils, and ultrastructural and morphological defects in mitochondria, including disturbances in the orientation and packing density of crista membranes, were detected. These malfunctions were improved by pretreatment with uridine (30 mg/kg, twice with an interval of 24 h, i.p.). Uridine also led to the normalization of the QT interval. Moreover, uridine effectively inhibited ISO-induced ROS overproduction and lipid peroxidation in rat heart mitochondria. The administration of uridine partially recovered the protein level of the respiratory chain complex V, along with the rates of ATP synthesis and mitochondrial potassium transport, suggesting the activation of the potassium cycle through the mitoKATP channel. Taken together, these results indicate that uridine ameliorates acute ISO-induced myocardial injury and mitochondrial malfunction, which may be due to the activation of mitochondrial potassium recycling and a mild uncoupling leading to decreased ROS generation and oxidative damage.

Functioning of the mitochondrial ATP-dependent potassium channel in rats varying in their resistance to hypoxia. Involvement of the channel in the process of animal's adaptation to hypoxia.

The mechanism of tissue protection from ischemic damage by activation of the mitochondrial ATP-dependent K(+) channel (mitoK(ATP)) remains unexplored. In this work, we have measured, using various approaches, the ATP-dependent mitochondrial K(+) transport in rats that differed in their resistance to hypoxia. The transport was found to be faster in the hypoxia-resistant rats as compared to that in the hypoxia-sensitive animals. Adaptation of animals to the intermittent normobaric hypoxia increased the rate of transport. At the same time, the intramitochondrial concentration of K(+) in the hypoxia-sensitive rats was higher than that in the resistant and adapted animals. This indicates that adaptation to hypoxia stimulates not only the influx of potassium into mitochondria, but also K(+)/H(+) exchange. When mitoK(ATP) was blocked, the rate of the mitochondrial H(2)O(2) production was found to be significantly higher in the hypoxia-resistant rats than that in the hypoxia-sensitive animals. The natural flavonoid-containing adaptogen Extralife, which has an evident antihypoxic effect, increased the rate of the mitochondrial ATP-dependent K(+) transport in vitro and increased the in vivo tolerance of hypoxia-sensitive rats to acute hypoxia 5-fold. The involvement of the mitochondrial K(+) transport in the mechanism of cell adaptation to hypoxia is discussed.