Abstract
Na,K‐ATPase represents the key enzyme that maintains the homeostasis of sodium and potassium ions in the cells. It was documented that in directly irradiated organs the activity of this enzyme is decreased. The aim of present study was to clarify the remote effect of irradiation in mediastinal area on the activity of the Na,K‐ATPase in kidneys in rats. Ionizing radiation in single dose 25 Gy resulted in consequent decrease of the body weight gain as well as the size of kidneys in Wistar rats. In addition, radiation induced alterations in the oxidative status of blood plasma. Irradiation also decreased the activity of renal Na,K‐ATPase. Measurements of enzyme kinetics that were dependent on the concentration of energy substrate ATP or cofactor Na+ indicated that the lowered enzyme activity is probably a consequence of decreased number of active molecules of the enzyme, as suggested by lowered V max values. Immunoblot analysis confirmed the lowered expression of the catalytic alpha subunit together with decreased content of the glycosylated form of beta subunit in the renal tissue of irradiated rats. The ability of the enzyme to bind the substrate ATP, as well as Na+ was not affected, as shown by unaltered values of K m and KN a. Irradiation of the body in the mediastinal area despite protection of kidneys by lead plates during application of X‐ray was followed by significant decline of activity of the renal Na,K‐ATPase, what may result in deteriorated homeostasis in the organism.
Highlights
Radiation therapy is commonly used therapeutic procedure in oncology
Formation of hydroperoxides in membranes would result in the damage of membranebound enzymes
Plasma protein concentration and biochemical analysis of oxidative status Total protein concentration in plasma was lower in irradiated rats compared with control (84 Æ 5 control vs. 59 Æ 5 irradiated, in g/L, P = 0.004)
Summary
The effects of radiation therapy are mediated, in addition to their direct impact on DNA, by the production of free radicals. Radiation-induced increase in free radicals results in lipid peroxidation, leading to structural and functional damage to cellular membranes (Purohit et al 1980). Formation of hydroperoxides in membranes would result in the damage of membranebound enzymes. One of these enzymes is the Na,KATPase or so called sodium pump. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.
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