Membrane ion transport as a target of low level ionizing radiation exposure

It had been shown that Na,K-pump function was changed under influence of various factors including ionising radiation. In that connection single and chronic irradiation effects on the active K+ transport were investigated in rat brain cortex slices. Wistar rats were irradiated with 1, 5, 15, 25 and 50 Gy acutely or chronically 1, 5, 15 25 and 50 day (1 cGy per day at dose rate of 0.037 mGy/s). In 1, 15 and 30 days after exposure the K+ transport was estimated as a difference between K+ contents in slices after 20 min preincubation, 10 min anaerobic incubation (passive k+ diffusion) and 30 min aerobic incubation (Na, K-pump activity). The total K+ amounts in the native cerebral tissue was measured in the initial slices immediately after preparation of them. In accordance to obtained data the both single and chronic irradiation caused oscillating changes in the Na,K-pump activity as while as dose means were increased, but phases and amplitudes of those oscillations were different. In 1 day after single exposure 1 and 25 cGy irradiation activated the Na,K-pump by 15.0 % and 19.4 % respectively, 5 and 15 cGy irradiation inhibited the Na,K-pump (by 21.2 % and 33 % accordingly), and 50 cGy irradiation had no obvious effect. In 30 day after irradiation the Na,K-pump activity was reduced to 58.4% from the control values in dose-dependent way. Oscillating changes in the active K+ transport induced by chronic irradiation were expressed more clearly and appeared after low dose exposures in case of the single irradiation with same doses. Peak of the Na,K-pump activation (by 29.9%) was obtained at the dose means of 15 cGy, whereas 25 cGy and 50 cGy irradiation reduced the active K+ transport rate by 25.7 % and 33.9 % accordingly. In 30 day after chronic ionizing exposures the K+ level was restored approximately to the control values. (author)