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OBJECTIVE: Electromagnetic fields can affect intracellular Ca(2+) levels. The aim of this study was to determine the changes intracellular Ca(2+) concentration in cardiac ventricle cells of rats exposed to 0.25 mT (2.5 Gauss) magnetic field. METHODS: Forty-five male rats were introduced to this study. The rats were divided into three groups: control, sham, and experiment. The experimental group was exposed to 0.25 mT extremely low frequency (ELF) magnetic field for 14 days, 3 h/day. The sham group was treated like the experimental group, except for elf-magnetic field exposure. The control group was not subjected to anything and differed from the experimental group and sham group. In the end of experiment, rats were sacrificed, cardiac tissue was removed, and these were fixed in 10% neutral formalin. Then, ventricular cells were stained by Alizarin red staining method. RESULTS: In the light microscopic examinations of control groups, in myofibril structures between groups, changes were not observed. In myofibril regions of the experimental group compared to other groups, increased heterogen Ca(2+) accumulations were found. CONCLUSION: ELF magnetic fields are used in daily life. The results of this study show that intracellular Ca(2+) accumulation in cardiac ventricles can increase in rats exposed to ELF magnetic field.

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Modulation of endogenous gene function, through sequence-specific recognition of double helical DNA via oligonucleotide-directed triplex formation, is a promising approach. Compared to the formation of pyrimidine motif triplexes, which require relatively low pH, purine motif appears to be the most gifted for their stability under physiological conditions. Our previous work has demonstrated formation of magnesium-ion dependent highly stable intermolecular triplexes using a purine third strand of varied lengths, at the purine•pyrimidine (Pu•Py) targets of SIV/HIV-2 (vpx) genes (Svinarchuk, F., Monnot, M., Merle, A., Malvy, C., and Fermandjian, S. (1995) Nucleic Acids Res. 23, 3831-3836). Herein, we show that a designed intramolecular version of the 11-bp core sequence of the said targets, which also constitutes an integral, short, and symmetrical segment (G(2)AG(5)AG(2))•(C(2)TC(5)TC(2)) of human c-jun protooncogene forms a stable triplex, even in the absence of magnesium. The sequence d-C(2)TC(5)TC(2)T(5)G(2)AG(5)AG(2)T(5)G(2)AG(5)AG(2) (I-Pu) folds back twice onto itself to form an intramolecular triple helix via a double hairpin formation. The design ensures that the orientation of the intact third strand is antiparallel with respect to the oligopurine strand of the duplex. The triple helix formation has been revealed by non-denaturating gel assays, UV-thermal denaturation, and circular dichroism (CD) spectroscopy. The monophasic melting curve, recorded in the presence of sodium, represented the dissociation of intramolecular triplex to single strand in one step; however, the addition of magnesium bestowed thermal stability to the triplex. Formation of intramolecular triple helix at neutral pH in sodium, with or without magnesium cations, was also confirmed by gel electrophoresis. The triplex, mediated by sodium alone, destabilizes in the presence of 5'-C(2)TC(5)TC(2)-3', an oligonucleotide complementary to the 3'-oligopurine segments of I-Pu, whereas in the presence of magnesium the triplex remained impervious. CD spectra showed the signatures of triplex structure with A-like DNA conformation. We suggest that the possible formation of pH and magnesium-independent purine-motif triplexes at genomic Pu•Py sequences may be pertinent to gene regulation.

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Release of 5-methylene-2-furanone (5-MF), a characteristic marker of DNA deoxyribose oxidative damage at the C1' position, was observed in significant quantities from X-irradiated DNA. This observation, which held for DNA irradiated either in aqueous solution or as a film, requires postirradiation treatment at 90 degrees C in the presence of polyamines and divalent metal cations at biological pH. The 5-MF product was quantified by using reverse-phase HPLC. The radiation chemical yield of 5-MF comprised more than 30% of the yield of total unaltered base release. Polylysine, spermine and Be(II) showed the strongest catalytic effect on 5-MF release, while Zn(II), Cu(II), Ni(II), putrescine and Mg(II) were substantially less efficient. We have hypothesized that the 5-MF release from irradiated DNA occurs through catalytic decomposition of the 2'-deoxyribonolactone (dL) precursor through two consecutive beta- and delta-phosphate elimination reactions. A stepwise character of the process was indicated by the S-shaped time course of 5-MF accumulation. If dL proves to be the precursor to 5-MF formation, it would then follow that dL is a very important lesion generated in DNA by ionizing radiation.

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