Development of (a human X-chromosome * hamster) hybrid cell assay system, which is sensitive to tritium exposure.

使用HPRT突变来测定辐射效应，因为可以通过用6-硫代鸟嘌呤和HAT（次黄嘌呤-氨基蝶呤-胸苷）的阳性-阴性选择来分离。然而，辐射常诱发DNA缺失型突变，这可能降低HPRT突变率。为了检测缺失突变，我们开发了HPRT缺陷仓鼠杂交细胞，其中一个intanct人类X染色体。实验表明，辐射后8-10天为细胞的适宜表达时间。经4-戈伊照射后，细胞突变率为450个突变体/10 ^5个存活细胞，而常规啮齿类动物实验系统的突变率为5-50个突变体/10 ^5个存活细胞。因此，新开发的测定系统显示出比用于测定辐射效应的灵敏度高10-100倍。经FISH分析证实，在突变细胞中存在一条转移的人染色体，提示HPRT基因可能诱发突变。突变发生率与γ-Co-γ射线辐射剂量呈线性关系<60>，其敏感性比常规HPRT法高近100倍。当将该发生率与氚-β射线的发生率进行比较时，生物有效性RBE显示与先前观察一致的值1.24。因此，我们的研究表明，具有完整的人类X染色体的仓鼠杂交细胞用于评价氚生物效应的高灵敏度和有用性。

HPRT mutation was used to assay the radiation effect, since it is possible to isolate by positeve-negative selection with 6-thioguanin and HAT (hypoxunthin-aminopterin-thymidine). Howeverr, radiation is known frequantly to induce DNA-deletion type mutation, which possibly decrease the HPRT mutation rate. To detect the deletion mutation, we developped HPRT deficient hamster-based hybrid cells, where an intanct human X-chromosome. was transfered our experiments showed that appropriate expression time of these cells is 8-10 days after irradiation. The mutation incidence of theses cells was 450 mutants/ 10^5 survived cells after 4-Gy irradiation and it was contrast with mutantion rate in conventional rodent assay system : 5-50 mutants/10^5 survived cells. Thus, newly developped assay system indicated 10-100 fold highre sesnsitivity than that used to assay for radiation effect. Existance of a transferred human chromosome in their mutant cells were confirmed by FISH ana1ysis, implying mutation induction with the of HPRT gene. Mutation incidences were linearly increased with radiation dose of ^<60>Co-gamma-rays and this dose-relationship showed the approxinately 100-fold high sensitivity, compared with that of conventional HPRT mutation assay. When this incidence was compared with that of tritium-beta rays, the biological effectiveness RBE indicated the consistent value, 1.24, with previous observation. As a results, our studies demonstrated the high sensitivity and usefulness of hamster hybrid cells cantaining an intact human X-chromosome for evaluation of tritium biological effects.