The activity of Na+, K+-ATPase and adenine nucleotides content in the heart muscle of rats under conditions of combined effect of ionizing radiation and intense physical exercise

Abstract

There is a high risk of radiation contamination of the environment due to warfare taking place on the territory of Ukraine. The impact of ionizing radiation on the body is often combined with heavy physical exertion, which significantly exacerbates its negative effects. Many systems of the living organism become compromised and in particular the cardiovascular system. Therefore, the aim of this article is to study the active ion transport systems functioning and the adenine nucleotides content in the mitochondrial fraction of the heart muscle from irradiated rats subjected to intense physical exercise.

Experimental studies were carried out on 50 sexually mature male Wistar rats. The animals were irradiated at a total dose of 154,8 mC/kg on a γ-therapeutic device AGAT-R No. 83 (isotope ⁶⁰Co) under the following technical conditions: source-field distance 75 cm, dose rate 0,385 mA/kg. After 1 hour, 1 day, and 3 days after the exposure, the rats were subjected to heavy physical exertion, which was simulated using a treadmill. When the animals refused to run, they were decapitated. In the mitochondrial fraction of cardiomyocytes, the activity of Na⁺,K⁺-ATPase, the content of adenine nucleotides, their ratio and adenylate energy charge were measured.

1 hour after total-body irradiation and intense physical exercise, the content of ATP and the activity of Na⁺,K⁺-ATPase decrease by 29% and 39%, respectively, compared to the control group. However, compared to the group of animals that underwent intense physical exertion only, these parameters remain relatively unchanged.

24 hours after the irradiation, there is a certain increase in the concentration of ATP and Na⁺,K⁺-ATPase enzyme activity in relation to the previous period by 24% and 13%, respectively. That indicates an activation of compensatory and adaptive mechanisms. Still, no complete normalization of energy levels and active ion transport through the cell membrane is observed.

The most prominent changes in the studied parameters are recorded on the 3rd day of the experiment, which coincides with the onset of acute radiation syndrome. There is a discharge of the adenylate energy system of the myocardial cells, which is evidenced by a significant decrease in the energy charge, ATP/ADP and ATP/AMP ratios. During this period, the activity of Na⁺, K⁺-ATPase is suppressed by 55% compared to the control group and by 19% in relation to non-irradiated exhausted animals.

The authors concluded that the effect of total-body gamma irradiation at a dose of 154,8 mCl/kg followed by intense physical exercise leads to a more significant suppression of Na⁺, K⁺-ATPase activity in the heart muscle of rats and to a disturbance in the adenylate energy system compared to the animals that underwent physical exertion only.

Negative changes in the studied indicators are determined by the time that has passed after the total-body gamma irradiation with a tendency to worsen on the 3rd day of the experiment.