Ornithine decarboxylase activity is regulated by a wide variety of growth factors and hormones active on the cell surface. Cyclic AMP and phorbol ester tumor promotors, in addition to other membrane-active compounds, have been shown to rapidly modulate ornithine decarboxylase activity. The tumor-promoting phorbol esters, including TPA used in this study, have a specific membrane receptor, the calcium-phospholipid kinase (protein kinase C). Since latent cell transformation manifested in the presence of phorbol esters has been reported following low-level microwave exposure, ornithine decarboxylase might be a sensitive molecular marker of field-related actions related to the process of tumor promotion.
|Chamber||The long axis of the Crawford cell was oriented vertically inside a large incubator at 37 ± 0.5°C.|
|Setup||Cell cultures of 10 ml in circular Petri dishes (75 cm²) were placed in a gas-tight Lucite box inside the Crawford cell near the center of the long axis at a distance of 1 cm from each other. Air containing 5% CO2 at 100% humidity was passed continuously into the Lucite culture chambers.|
|Sham exposure||A sham exposure was conducted.|
|Additional info||Control cultures were placed in the same incubator in a similar box outside the Crawford cell.|
In all three cell types, a 1-h radiation produced a significant (up to 50%) increase in ornithine decarboxylase activity in comparison to the unexposed cultures. Following removal from the field, ornithine decarboxylase activity remained elevated in the exposed cells for more than a 3-h period in the Reuber H35 and CHO cells (the increase in the 294T cells persisted for only 1 h).
Modulation frequencies of 60 and 100 Hz failed to cause any alteration in ornithine decarboxylase activity in Reuber H35 cells following a 1-h radiation, in contrast to the 50% increase in enzyme activity brought about the 16 Hz modulated field.
The stimulated ornithine decarboxylase activity in the cultured cells that followed treatment with a phorbol ester tumor promotor (TPA) was potentiated by prior exposure to the same low energy electromagnetic field.The field did not alter either basal or TPA-stimulated DNA synthesis.