Yukiko Okada

Cell surface measurements of ATP release from single pancreatic beta cells using a novel biosensor technique.

Abstract To examine the possibility that ATP modulates insulin secretion by an autocrine mechanism, we measured the local concentration of released ATP at the surface of a single pancreatic β cell by a new biosensor technique, using PC12 cells expressing ligand-gated cation channels, P2X2 receptors. Upon application of glucose or glibenclamide, a series of current spikes, whose amplitude equates to an ATP concentration of over 25 µM, were recorded from a PC12 cell using the whole-cell patch-clamp technique, when placed near a rat pancreatic β cell at 37°C. The current response was inhibited by cooling (below 30°C) or by applying an ATP-hydrolysing enzyme (apyrase) or a P2 receptor blocker (suramin). Thus, it is concluded that pancreatic β cells secrete ATP in response to glucose stimulation, thereby increasing the ATP concentration close to the cell surface sufficiently high enough to enhance insulin secretion from the pancreatic β cells.

Fractionation of radiocesium in soil, sediments, and aquatic organisms in Lake Onuma of Mt. Akagi, Gunma Prefecture using sequential extraction.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has resulted in the contamination of the environment in Gunma Prefecture with radioisotope cesium (radio-Cs, 134Cs and 137Cs). Concentrations of radio-Cs >500Bqkg-1 were found in wakasagi (Hypomesus nipponensis) in Lake Onuma at the top of Mount (Mt.) Akagi in August 2011. To explain the mechanism of this contamination, monitoring studies have been conducted around Lake Onuma by measuring radio-Cs concentrations in samples of fish, aquatic plants, plankton, lake water, lake sediments, and surrounding soil. The leachability of radio-Cs was evaluated using sequential extraction by Tessier et al. The total concentration of radio-Cs in Lake Onuma ecosystems decreased gradually with time. In the brown forest soil, radio-Cs concentrations of 2000 to 6000Bqkg-1 were detected. The abundance ratio of the easy-elution form (exchangeable and carbonate forms) in the samples was <10%. The concentrations in phytoplankton samples were 3-6 times higher than those in wakasagi samples. The ratios of easy-elution forms increased by the rank in the food chain; 37% in phytoplankton, 78% in zooplankton, and 97% in wakasagi. It is likely that the lower ratio of the easy-elution form in phytoplankton is related to the adsorption of radio-Cs on suspended substances in the lake, as suggested by the analyses of aluminum and titanium in the phytoplankton, zooplankton, and wakasagi samples. The high concentrations of radio-Cs in wakasagi would be related also to the characteristics of closed mountain lakes.

Certified reference materials of agricultural products and foods bearing radioactivity from the Fukushima nuclear accident

Abstract Certified reference materials (CRMs) for food analysis were developed in an inter-laboratory experiment for validation of measurement of radiocesium in foodstuffs. Since 2012, five series of CRMs were developed, including for brown rice grain, soybean powder, beef flake, shiitake mushroom powder and marine fish (meat and bone parts). This paper discusses the strategy of development, including choice of CRMs developed and the preparation and certification procedures applied for CRM development. In particular, some detailed data are presented for the most popular CRMs developed: brown rice grain, soybean powder and beef flake.

Natural alpha-active isotopes contained in modern memory device materials

Coprecipitation methods with SmF3 and BaSO4 were developed in order to evaluate the radioequilibrium of natural decay nuclides series in high purity silica and lead. The present study revealed that228Th,230Th, and231Pa in silica and210Po, probably210Pb, in lead were enriched in much higher concentrations than their precursor nuclides.

Radiocesium dynamics in the aquatic ecosystem of Lake Onuma on Mt. Akagi following the Fukushima Dai-ichi Nuclear Power Plant accident.

Understanding ecosystem dynamics of radionuclides is necessary to ensure effective management for food safety. The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident on March 11, 2011 released large amounts of radiocesium (134Cs and 137Cs) and contaminated the environment across eastern Japan. In this study, we aimed to elucidate the temporal dynamics of 137Cs in the aquatic ecosystem of Lake Onuma on Mt. Akagi. The effective ecological half-life (Teff) of 137Cs in fishes, western waterweed (Elodea nuttallii), seston (phytoplankton and zooplankton), and lake water was estimated using survey data of 137Cs concentration collected from 2011 to 2016, and single- and two-component decay function models (SDM and TDM, respectively). The decay processes of 137Cs concentrations in wakasagi (Hypomesus nipponensis), pale chub (Zacco platypus), phytoplankton, and total 137Cs concentrations of the water column (WC) in the lake were well suited by the TDMs. The Teff in the fast component of the TDMs in these samples ranged from 0.49 to 0.74years. The Teff in the slow component of the TDMs could converge towards the physical half-life of 137Cs. Nearly five and a half years after the FDNPP accident, we concluded that 137Cs concentrations approached a state of dynamic equilibrium between some aquatic organisms (wakasagi, pale chub, and phytoplankton) and the environment (lake water). However, the decay processes of 137Cs concentrations in Japanese dace (Tribolodon hakonensis), western waterweed, zooplankton, and particulate- and dissolved-forms in the WC were better predicted for the SDM. The total 137Cs concentrations in inflowing river and spring waters were one to two orders of magnitude lower than lake water under normal flow conditions. However, particulate 137Cs contamination level in the river water was high after heavy rains. Overall, 137Cs contamination levels have significantly decreased in Lake Onuma, but monitoring surveys should be continued for further understanding of the reduction processes.

Preparation and certification of certified reference materials of fish meat and ashed bone for determination of 90Sr and radiocesium after Fukushima Daiichi Nuclear Power Plant

Certified reference materials (CRMs) of the fish meat powder and the fish bone ash for validation of measurement of anthropogenic nuclides (134Cs, 137Cs and 90Sr) related the Fukushima Daiichi nuclear power plant accident were developed using an inter-laboratory comparison. This paper discusses the strategy of development including selection of raw material, the preparation and certification procedures applied for CRM production. In particular, some detailed data are presented for the homogeneity study and inter-laboratory experiment for the certification. The results of inter-laboratory comparison not only to certify CRMs but also showed analytical performance of the anthropogenic nuclides in Japanese laboratories.

Construction of 1.7 MV Pelletron Tandem Accelerator System and Its Application to Human Resource Development at Tokyo City University Atomic Energy Research Laboratory

Naoto HAGURA, Noriyosu HAYASHIZAKI, Takafumi UCHIYAMA, Yoshiyuki OGURI, Hitoshi FUKUDA, Katsunori KAWASAKI, Tamotsu TORIYAMA, Koichi MOCHIKI, Yukiko OKADA, Jun KAWARABAYASHI, Ishi MITSUHASHI and Haruaki MATSUURA 1 Department of Nuclear Safety Engineering, Tokyo City University, 1-28-1 Tamazutsumi, Setagaya-ku, Tokyo 158-8557, Japan 2 Atomic Energy Research Laboratory, Tokyo City University, 971 Ozenji, Asao-ku, Kawasaki, 215-0013, Japan 3 Laboratory for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan 4 Technical Department, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan 5 Electrostatic Accelerator Research Laboratory, 3-1-22-P2-502 Honcho, Higashikurume-city, Tokyo 203-0053, Japan 6 Laboratory for Materials Engineering with Quantum Beams, 4-2-17 Nishigahara, Kita-ku, Tokyo 114-0024, Japan

Comparative analysis of distributions of radioactive cesium and potassium and stable cesium, potassium, and strontium in brown rice grains contaminated with radioactive materials released by the Fukushima Daiichi Nuclear Power Plant accident

The distributions of 137Cs, 134Cs, and 40K as well as stable Cs, K, and Sr in bran, germ, and endosperm of brown rice contaminated by fallout from the Fukushima Daiichi Nuclear Power Plant were studied. It was found that 137Cs, 134Cs, and 40K were accumulated in germ at the highest concentration and the concentration ratios of Cs and K in bran, germ, and endosperm were approximately identical to one another, while the highest concentration of Sr was detected for bran. Possible chemical forms of the metal elements in rice grains were discussed based on their extraction behavior with water and MgCl2 aqueous solution.