A small temperature rise may contribute towards the apparent induction by microwaves of heatshock gene expression in the nematode Caenorhabditis elegans

Dawe, Adam S.; Smith, Brette; Thomas, David W.P.; Greedy, Steve; Vasic, Nebojsa; Gregory, Andrew; Loader, Benjamin; de Pomerai, David I.

Abstract

We have previously reported that low-intensity microwave exposure (0.75-1.0 GHz CW at 0.5 W; SAR 4-40 mW kg-1) can induce an apparently non-thermal heat-shock response in Caenorhabditis elegans worms carrying hsp16-1::reporter genes. Using matched copper TEM cells for both sham and exposed groups, we can detect only modest reporter induction in the latter (15-20% after 2.5 h at 26°C, rising to ~50% after 20 h). Traceable calibration of our copper TEM cell by the National Physical Laboratory (NPL) reveals significant power loss within the cell (8.5% at 1.0 GHz), accompanied by slight heating of exposed samples (~0.3°C at 1.0 W). Thus exposed samples are in fact slightly warmer (by ≤0.2°C at 0.5 W) than sham controls. Following NPL recommendations, our TEM cell design was modified with the
aim of reducing both power loss and consequent heating. In the modified silver-plated cell, power loss is
only 1.5% at 1.0 GHz, and sample warming is reduced to ~ 0.15°C at 1.0 W (i.e. ≤ 0.1°C at 0.5 W). Under sham:sham conditions, there is no difference in reporter expression between the modified silverplated TEM cell and an unmodified copper cell. However, worms exposed to microwaves (1.0 GHz and 0.5 W) in the silver-plated cell also show no detectable induction of reporter expression relative to sham controls in the copper cell. Thus the 20% “microwave induction” observed using two copper cells may be
caused by a small temperature difference between sham and exposed conditions. In worms incubated for 2.5 h at 26.0, 26.2 and 27.0°C (with no microwave field), there is a consistent and significant increase in reporter expression between 26.0 and 26.2°C (by ~20% in each of 6 independent runs), but paradoxically expression levels at 27.0°C are similar to those seen at 26.0°C. This surprising result is in line with other evidence pointing towards complex regulation of hsp16-1 gene expression across the sub-heat-shock range of 25-27.5°C in C. elegans. We conclude that our original interpretation of a non-thermal effect of microwaves cannot be sustained; at least part of the explanation appears to be thermal.

Citation

Dawe, A. S., Smith, B., Thomas, D. W., Greedy, S., Vasic, N., Gregory, A., Loader, B., & de Pomerai, D. I. (2006). A small temperature rise may contribute towards the apparent induction by microwaves of heatshock gene expression in the nematode Caenorhabditis elegans. Bioelectromagnetics, 27(2), https://doi.org/10.1002/bem.20192

• Journal Article Type: Article
• Publication Date: Feb 1, 2006
• Deposit Date: Jun 14, 2013
• Publicly Available Date: Jun 14, 2013
• Journal: Bioelectromagnetics
• Print ISSN: 0197-8462
• Electronic ISSN: 1521-186X
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 27
• Issue: 2
• DOI: https://doi.org/10.1002/bem.20192
• Public URL: https://nottingham-repository.worktribe.com/output/1018491
• Publisher URL: http://onlinelibrary.wiley.com/doi/10.1002/bem.20192/abstract
• Additional Information: The definitive version is available at: www3.interscience.wiley.com