as measured by quantitative microdensitometry of northern blots. The field strengths used by Liburdy and co-workers were much higher than those used by Goodman and co-workers and were several orders of magnitude above those reported for residential exposures.
Studies by Czerska et al. (1992) also indicated that human lymphocytes (Daudi cell line) showed increased myc expression when exposed to field strengths similar to those used by Goodman and co-workers; in Czerska et al. (1992), the internal control ß-actin was found to be unaltered (although in the Goodman et al. studies, ß-actin appeared to be stimulated at the same field strengths as myc and other markers). None of the experiments reported in this section appears to have been carried out using blinded experimental protocols, and there has been considerable criticism of the lack of precision of some methods and the lack of consistent internal or external controls in many of the gene-expression experiments, particularly those in the Goodman et al. studies.
In response to those criticisms, at least two groups set out to perform rigorous replication studies of the findings reported by Goodman and co-workers. As reported in two current publications (Saffer and Thurston 1995; Lacy-Hulbert et al. 1995), as well as in several abstracts presented at meetings, these groups used the original equipment, exposures, and cellular end points (including experiments done in the laboratories of Goodman and Shirley-Henderson) and a more-sophisticated exposure apparatus, along with more-specific and sensitive detection techniques, to examine the claims of increased gene transcription induced by power-frequency magnetic fields. In Saffer and Thurston's (1995) study, the original exposure conditions and an extended range of exposures were used (5.7-100 µT); a number of refinements were also introduced to eliminate possible evaluator bias (double blinding) and nonuniformity of exposures (double-wrapped, double-blinded exposure coils) and to improve experimental techniques (loading techniques for RNA and internal and external standards) and detection methods (northern blots, differential display, and ribonuclease protection assays). In addition, a number of different strains of HL-60 cells (including the strain provided by Goodman and Shirley-Henderson used for the original findings) as well as Daudi cells were used. The net result of these studies was that no significant effect of magnetic-field exposure could be detected in any of the genes examined under any of the exposure conditions used. The positive control TPA was used to demonstrate that small effects on transcription could be observed under the conditions used, and a number of internal controls were used to verify the minimum levels of changes in expression that could be detected. Changes in the range of 10% could have been detected reliably, but none was found. This finding is in contrast to the increases of 30-280% reported by Goodman and co-workers in their studies. In addition to in-depth studies with c-myc and other genes used by Goodman and co-workers, Saffer and Thurston (1995) carried out differential-display polymerase-chain-reaction (PCR) analysis on HL-60 cells exposed to magnetic fields to determine whether any gene transcripts in the cell could be