Increased ornithine decarboxylase activity in cultured cells exposed to low energy modulated microwave fields and phorbol ester tumor promoters.

Ornithine decarboxylase (ODC) is present in all nucleated cells and is the rate-limiting enzyme for synthesis of polyamines. In turn, the polyamines are required for DNA synthesis and cell growth. In Reuber H35 hepatoma cells, we show that ODC activity is increased by about 50% during exposure to a 1-h "athermal" (less than 0.1 degree C temperature rise) (450 MHz, 1.0 mW/cm2 peak-envelope-power) microwave field sinusoidally amplitude-modulated at 16 Hz. The increased activity of ODC persisted for several hours following the 1-h exposure to the field. A similar field amplitude-modulated at 60 and 100 Hz did not alter the hepatoma cell ODC activity. The stimulated ODC activity in the cultured cells that followed treatment with a phorbol ester tumor promoter (12-O-tetradecanoylphorbol-13-acetate) was further potentiated by prior exposure to the same low energy electromagnetic field. This field did not alter either basal or 12-O-tetradecanoylphorbol-13-acetate-stimulated DNA synthesis. We observed a similar increase in the basal ODC activity of cultures of two additional cell lines (Chinese hamster ovary; and 294T melanoma) exposed for 1 h to the amplitude-modulated field. Chinese hamster ovary cells exposed to the radio frequency field for 1 h also responded to subsequent treatment with 12-O-tetradecanoylphorbol-13-acetate by exhibiting a further increase in ODC activity. We have observed previously that the activity of this enzyme is increased in cultured cells following a transient exposure to a 60-Hz electric field. Altered ODC activity may serve as a sensitive and specific molecular marker of the transductive coupling of weak pericellular electromagnetic fields to biological systems.