Annual Report

12. Low-Dose Irradiation Influences Ca2+ Signaling in Cultured Rat Hepatocytes

Tetsuo Nakajima, Bing Wang, Masako Nose, Hiromi Itsukaichi, Harumi Ohyama and Osami Yuakawa

Keywords: rat hepatocytes, low-dose effect, Ca2+ signaling, adaptive response

We have already demonstrated that radiation induces diacylglycerol(DAG) production by phosphoinoside-specific phospholipase C(PI-PLC) and protein kinase C activation in cultured rat hepatocytes. Since DAG production by PI-PLC is accompanied by the production of inositol 1,4,5-trisphosphate(IP3), which works in Ca2+ signaling, radiation might influence Ca2+ signaling in the cells. On the other hand, we have previously reported that, in cultured rat hepatocytes, low-dose irradiation (0.05-0.1 Gy) induces the increase of intracellular radical scavenging ability in relation to adaptive response. In this study, the effect of low-dose irradiation on Ca2+ signaling in rat hepatocytes was investigated as compared with the effect of high-dose irradiation on it. No change in the cytosolic Ca2+ concentration ([Ca2+]i.) was observed after irradiation of hepatocytes with 0.1 Gy of X-rays. However, the irradiation prolonged the time for restoration of ATP-induced [Ca2+]i uptake to the basal [Ca2+]i level in the cells compared with that in non-irradiated cells. High-dose irradiation with 10 Gy did not have any effect on the time for the restoration of ATP-induced [Ca2+]i uptake to the basal level in the cells, but reduced the level of the ATP-induced [Ca2+]i uptake. In contrast, low-dose irradiation with 0.1 Gy did not change the level of the ATP-induced [Ca2+]i uptake. The prolonged time in ATP-induced [Ca2+]i uptake suggests that low-dose irradiation might specifically influence Ca2+ signaling and induce adaptive response.

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