We tested the hypothesis that early alterations in calcium influx induced by an imposed 60 Hz magnetic field are propagated down the signal transduction (ST) cascade to alter c‐MYC mRNA induction. To test this we measured both ST parameters in the same cells following 60 Hz magnetic field exposures in a specialized annular ring device (220 G (22 mT), 1.7 maximal E induced, 37°C, 60 min). Ca2+ influx is a very early ST marker that precedes the specific induction of mRNA transcripts for the proto‐oncogene c‐MYC, an immediate early response gene. In three experiments influx of 45Ca2+ in the absence of mitogen was similar to that in cells treated with suboptimal levels of Con‐A (1 ). However, calcium influx was elevated 1.5‐fold when lymphocytes were exposed to Con‐A plus magnetic fields; this co‐stimulatory effect is consistent with previous reports from our laboratory [FEBS Lett. 301 (1992) 53‐59; FEBS Lett. 271 (1990) 157‐160; Ann. N.Y. Acad. Sci. 649 (1992) 74‐95]. The level of c‐MYC mRNA transcript copies in non‐activated cells and in suboptimally‐activated cells was also similar, which is consistent with the above calcium influx findings. Significantly, lymphocytes exposed to the combination of magnetic fields plus suboptimal Con‐A responded with an approximate 3.0‐fold increase in band intensity of c‐MYC mRNA transcripts. Importantly, transcripts for the housekeeping gene GAPDH were not influenced by mitogen or magnetic fields. We also observed that lymphocytes that failed to exhibit increased calcium influx in response to magnetic fields plus Con‐A, also failed to exhibit an increase in total copies of c‐MYC mRNA. Thus, calcium influx and c‐MYC mRNA expression, which are sequentially linked via the signal transduction cascade in contrast to GAPDH, were both increased by magnetic fields. These findings support the above ST hypothesis and provide experimental evidence for a general biological framework for understanding magnetic field interactions with the cell through signal transduction. In addition, these findings indicate that magnetic fields can act as a co‐stimulus at suboptimal levels of mitogen; pronounced physiological changes in lymphocytes such as calcium influx and c‐MYC mRNA induction were not triggered by a weak mitogenic signal unless accompanied by a magnetic field. Magnetic fields, thus, have the ability to potentiate or amplify cell signaling.

An analogue of the homopyrimidine oligodeoxyribonucleotide d(CT)8 has been synthesized. This analogue, d(CT)8 contains nonionic methylphosphonate internucleoside linkages. The pH-dependent conformational transitions of d(CT)8 have been studied and its ability to form duplexes and triplexes with the normal homopurine oligonucleotide d(AG)8 has also been investigated as a function of pH. Circular dichroism spectroscopy and ethidium bromide fluorescence enhancement have been used to monitor pH-dependent conformational transitions driven by the protonation of cytosine residues, and the different behavior of d(CT)8 and d(CT)8 has been compared. It was possible to form self-associated complexes by using either d(CT)8 or d(CT)8, and both compounds combined with d(AG)8 to form duplex or triplex DNA. At neutral pH, the CD spectrum of d(AG)8.d(CT)8 duplex was quite different from the CD spectrum of d(AG)8.d(CT)8 duplex, reflecting most likely a difference in conformation. The duplex to triplex transition characteristic of this DNA sequence occurred at a lower pH when d(CT)8 was substituted for d(CT)8; however, at pH 4.2, triplex containing d(CT)8 was similar in conformation to triplex containing d(CT)8. Several of these observations can be related to the alterations in electrostatic and steric interactions that occur when the negatively charged phosphodiester backbone of d(CT)8 is replaced with a nonionic methylphosphonate backbone.

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Responses specific to the spin-spin relaxation time (T2) have been observed in two time-dependent studies of the intracellular water in normal and transformed Syrian hamster fetal fibroblasts. At 300-MHz (7.0 T), the spin-lattice relaxation time (T1) was insensitive to several aspects of cellular physiology that produced changes in the T2 and the apparent self-diffusion coefficient (Dapp) of intracellular water. In normal cells stimulated with epidermal growth factor (EGF), T1 was insensitive to time-dependent changes detected by T2 and Dapp. In synchronized tumor cells, T1 was insensitive to cell-cycle-dependent changes detected by T2. The strongly coupled behavior of T2 and Dapp that was observed as a function of time in EGF-stimulated cells indicates that the diffusion of intracellular water through inhomogeneous local magnetic field gradients produced effects observable in T2. Conformational changes in large intracellular macromolecular assemblies such as chromatin or the cytoskeleton may alter the magnitude and inhomogeneity of local field gradients, producing responses in T2 and Dapp only.