Arlett C F, Turnbull D, Harcourt S A, Lehmann A R, Colella C M
Mutat Res. 1975 Dec;33(2-3):261-78. doi: 10.1016/0027-5107(75)90202-x.
The forward mutation selection system based on resistance to 8-azaguanine has been widely used with cells cultured from a diversity of species and with a variety of mutagens. Ouabain resistance is an alternative selective system. Both systems show a substantial influence of expression time on the number of resistant variants observed after addition of the selective agent such that the frequency reaches a maximum which is dose dependent, and then declines rapidly. Metabolic cooperation has been propsed as the mechanism responsible for this decline with the 8-azaguanine system, but it is less likely to account for the loss of ouabain-resistant variants where it is necessary to invoke generalised effects on the viability of variants due to overcrowding on the plates. A comparison of the two selective systems showed that, with the exception of gamma-irradiation, which was apparently non-mutagenic in the ouabain system, there was broad agreement between the two systems for each mutagen tested. Ethyl methanesulphonate was the most efficient mutagen by a substantial factor. Ouabain resistance permitted greater discrimination particularly between weak mutagens because of the low frequency of spontaneous variants (4 x 10(-7) and also produced data with less intrinsic variability. The absence of gamma ray induced mutation in the ouabain system shows that it may fail to detect certain types of mutagens. Thus the two systems should be used to complement each other. Mutation by the fungicide captan was evaluated using both systems and the positive results indicate that it may pose a hazard to man.
基于对8-氮杂鸟嘌呤抗性的正向突变选择系统已广泛应用于多种物种培养的细胞以及各种诱变剂。哇巴因抗性是另一种选择系统。这两种系统都显示出表达时间对添加选择剂后观察到的抗性变体数量有重大影响，即频率达到最大且与剂量相关，然后迅速下降。代谢协同作用被认为是8-氮杂鸟嘌呤系统中这种下降的机制，但在哇巴因抗性变体的损失方面，它不太可能是原因，因为需要考虑平板上过度拥挤对变体活力产生的普遍影响。对这两种选择系统的比较表明，除了在哇巴因系统中明显无诱变作用的γ射线外，对于所测试的每种诱变剂，两种系统之间有广泛的一致性。甲磺酸乙酯是效率最高的诱变剂，优势明显。由于自发变体频率较低（4×10⁻⁷），哇巴因抗性允许进行更大程度的区分，特别是在弱诱变剂之间，并且产生的数据内在变异性较小。哇巴因系统中没有γ射线诱导的突变表明它可能无法检测到某些类型的诱变剂。因此，这两种系统应相互补充使用。使用这两种系统评估了杀菌剂克菌丹的诱变作用，阳性结果表明它可能对人类构成危害。
