To investigate the effects of extremely low frequency magnetic field and/or gamma rays radiation on the induction of the 6-thioguanine resistent mutation in the hypoxanthine-guanine phosphoribosyl transferase gene in human melanoma cells.
The hypoxanthine-guanine phosphoribosyl transferase (HPRT) is an enzyme in the purine (for example guanine) synthesis pathway. HPRT-negative cells are not able to use guanine for GTP synthesis und thus, they have to synthesize the base de novo. Using the guanine analog 6-thioguanine HPRT-positive cells use 6-thioguanine for nucleotide synthesis. However, integration of 6-thioguanine leads to DNA and RNA damage and it is lethal for these cells. In contrast, HPRT-negative cells are not able to utilize 6-thioguanine and survive.
The HPRT gene mutation assay is a well-established mutagenicity assay based on the selection of clones resistant to the purine analog 6-thioguanine. I.e. for determination of the induction of 6-thioguanine resistant mutation in the HPRT gene exposed cells are plated in a medium containing 6-thioguanine.
Hydoxyurea and arabinofuranosylcytosine were used to inhibit DNA synthesis.
Extremely low frequency magnetic field exposure alone and in combination with X-rays (3 Gy) were performed.
The experiments were repeated twice.
|Chamber||The incubator was inserted into the inner space of the core. Magnetic field was homogeneous within 1% difference for the area housing four 10 cm or ten 6 cm culture dishes.|
|Setup||A pair of magnetic cores (240 x 340 mm) made of silicon steel strips, 40 mm apart . Two copper coils (10 x 20 mm²) penetrate into the silicon steel core. An acrylic Incubator housing the plates was installed into the inner space of the core.|
|Additional info||For control experiments, a conventional incubator in a separate room was used.|
The mutant frequency of the hypoxanthine-guanine phosphoribosyl transferase gene was increased in cells exposed to extremely low frequency magnetic fields dependend on exposure time and the induced current intensities.
Mutations induced by gamma rays radiation were enhanced by post exposure to extremely low frequency magnetic fields.
The exposure to extremely low frequency magnetic fields did not affect both cell killing and cell growth.
Gamma rays radiation killing was not enhanced by extremely low frequency magnetic fields exposure.