Mesenchymal mouse stem cells were exposed to Terahertz waves to study whether mammalian cells exhibit specific cellular and/or molecular effects, unrelated to the temperature changes. To examine the eventual thermal effect locally, i.e. in the cells, the Terahertz-induced transcriptional activation of hyperthermic genes was quantified, and their expression levels were compared with previously reported differentially expressed genes (Bock et al. 2010).
The irradiations were performed at biologically-low temperatures (26-27°C), and at low Terahertz power densities (1-3 mW/cm²), in order to minimize thermal effects on the gene activity. To analyze the possible changes in the temperature, simulations and experimental measurements were applied.
Modulation type: pulsed
Exposure duration: continuous for 2 h or 9 h
Modulation type: CW
Exposure duration: continuous for 2 h
|Pulse width||0.035 ps|
|Repetition frequency||1 kHz|
|Exposure duration||continuous for 2 h|
|power density||3 mW/cm²||-||measured||-||at the center of the beam|
No cell death was visually observed. No effects on the cell membranes were visually discernable. No lipid inclusions were found in the control samples or in the samples that were exposed to 2 hours of CW irradiation (exposure 2). However, lipid droplet-like inclusions were observed in the cellular cytoplasm after 2 and 9 hours of broad-band exposure (exposure 1) and the morphological changes seemed to be dependent of the exposure duration (fewer inclusions after 2 h than after 9 h) and frequency.
Temperature increases were minimal, and the expression of the investigated heat shock proteins (hsp105, hsp90 and CPR) was unaffected, while the gene expression of the other genes (adiponectin, GLUT4, and PPARG) showed clear effects of the Terahertz irradiation after prolonged, broad-band exposure (as revealed in Bock et al. 2010). These effects where observed under irradiation conditions that caused minimal temperature changes, and in the explicit absence of any discernable response of heat shock and cellular stress genes.