Spontaneous mutation at the adenine phosphoribosyltransferase locus in human lymphoblastoid cells

112 Mutagenic activities per cubic meter were 20-81 times higher in the living rooms of smokers than of non-smokers. The indoor mutagenic activity was highly correlated with the number of cigarettes smoked ( P < 0 . 0 1 ) . No differences in indoor mutagenic activity were observed between laboratories.

73 Tatsumi, K., A. Fujimori, A. Tachibana, I. Arita and H. Takebe, Department of Molecular Oncology, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606 (Japan) Spontaneous mutation at the adenine phosphoribosyltransferase locus in human lymphoblastoid cells An assay system using microtiter plates has been developed to measure the frequency of mutations at the adenine phosphoribosyltransferase (APRT) locus on the human autosomal chromosome 16. An EBV-transformed B-lymphoblastoid cell line, WR10, was selected for the assay from cell lines derived from heterozygous carriers of hereditary 2,8-dihydroxyadenine urolithiasis (APRT deficiency). The baseline frequency of cells resistant to 100 /~M of 2,6-diaminopurine (DAP) was found to be 1.1 × 10 -5. The measurement of spontaneous mutation rate based on the mean calculation of the fluctuation test of Luria and Delbruck was 1.65 × 10-6/cell/generation. A P R T activities in 16 spontaneously DAP-resistant clones were found to vary between 0 and 38%, the level observed in aprt +/- WR10 cells. We found that WR10 cells were also heterozygous for SphI restriction fragment length polymorphism at the APRT locus, which allowed the functional and non-functional APRT alleles to be differentiated by Southern blot analysis. A majority of spontaneous DAP Tmutant clones examined (12/16, 75%) were associated with the loss of the functional allele.

74 The Collaborative Study Group for the Micronucleus Test (CSGMT, Organizer in chief: S. Sato, Japan Tobacco Inc.)

Single versus multiple dosing in the micronucleus test: summary of the fourth collaborative study by CSGMT/JEMS.MMS The effects of multiple dosing in the micronucleus test were studied by treating male CD-1 mice 1, 2, and 4 times i.p. with various doses of 11 chemicals and by sampling bone marrow cells 6, 24, 48, a n d / o r 72 h after the final dosing. The chemicals were roughly categorized into 4 groups: (1) 2-AAF, EMS, and K2CrO 4, which show no multiple-dosing effect; (2) metabolic inhibitors and base analogues such as ara-C, 5-FU, 6-MP, and MTX, which show a clear multiple-dosing effect; (3) chemicals such as benzene, DMBA, and ENU, which tend to show a multiple-dosing effect but also tend to show bone marrow depression; (4) phenacetin, which shows a multiple-dosing effect only after 2 or 3 doses without bone marrow depression. The original method of Schmid (1975), 2 doses and sampling 6 h after the second injection, was less sensitive than the modified method, i.e., sampling 24 h after the second dose. The latter regimen is recommended for general screening for the following reasons. (1) It was the most sensitive protocol of those tested here. (2) Since bone marrow specimens were prepared at or near the steady state of micronuclei, one sampling covered most chemicals with different actions. (3) For chemicals showing bone marrow depression after multiple dosing, specimens could be prepared before the depression became excessive. (4) Chemicals having no multiple-dosing effect showed a similar incidence of micronuclei after 1 and 2 doses. (5) Dose selection is much easier than with more frequent dosing.

75 Toda, S., Y. Suzuki l, I. Kawasaki and H. Shimizu 1, Mutagenicity Test Division, Biomedical Laboratories Inc., Kawagoe, Saitama 350 and 1 Department of Public Health, Jikei University School of Medicine, Minatoku, Tokyo 105 (Japan) Effect of pH value of phosphate buffer in Giemsa staining on the micronucleus test The aim of this study was to prove an influence of pH condition on Giemsa staining in the micro-