In vitro lymphocyte proliferation induced by radio-frequency electromagnetic radiation under isothermal conditions

Whole human blood was exposed or sham-exposed in vitro for 2 h to 27 or 2,450 MHz radio-frequency electromagnetic (RF) radiation under isothermal conditions (i.e., 37 +/- 0.2 degrees C). Immediately after exposure, mononuclear cells were separated from blood by Ficoll density-gradient centrifugation and cultured for 3 days at 37 degrees C with or without mitogenic stimulation by phytohemagglutinin (PHA). Lymphocyte proliferation was assayed at the end of the culture period by 6 h of pulse labeling with 3H-thymidine (3H-TdR). Exposure to radiation at either frequency at specific absorption rates (SARs) below 50 W/kg resulted in a dose-dependent, statistically significant increase of 3H-TdR uptake in PHA-activated or unstimulated lymphocytes. Exposure at 50 W/kg or higher suppressed 3H-TdR uptake relative to that of sham-exposed cells. There were no detectable effects of RF radiation on lymphocyte morphology or viability. Notwithstanding the characteristic temperature dependence of lymphocyte activation in vitro, the isothermal exposure conditions of this study warrant the conclusion that the biphasic, dose-dependent effects of the radiation on lymphocyte proliferation were not dependent on heating.     

Insertional inactivation of streptolysin S expression in Streptococcus pyogenes

The inactivation of a genetic determinant critical for streptolysin S production was accomplished by transfer and insertion of the transposon Tn916 into the DNA of a group A streptococcal strain. The group D strain CG110 was able to efficiently transfer Tn916 into the group A strain CS91 when donor and recipient cells were concentrated and incubated together on membrane filters. Among tetracycline-resistant transconjugants, nonhemolytic mutants that no longer produced streptolysin S and retained the capacity to produce streptolysin O were discovered. Hemolytic revertants from these mutants regained tetracycline sensitivity; other revertants still retained a tetracycline resistance phenotype. Hybridization studies employing Tn916 DNA located Tn916 sequences in EcoRI and HindIII fragments of DNA from mutants devoid of streptolysin S; one carried a single copy of Tn916, and the other two carried multiple copies of the transposon.     

Effects of X-band microwave exposure on rabbit erythrocytes

Rabbit erythrocytes were exposed in vitro to continuous wave (CW) and pulse-modulated X-band microwaves in wave guide exposure chambers. Erythrocytes were exposed as whole (hep-arinized) blood suspensions or as washed cells in 1:1 isotonic buffered K⁺-free saline suspensions. Statistically significant increases in K⁺ efflux relative to thermal controls were detected when red cells were exposed in whole blood suspensions to either CW or pulsed 8.42-GHz microwaves at SARs that resulted in equilibrium sample temperatures of approximately 24 °C. Under the same exposure conditions, no statistically significant K⁺ efflux occurred in the case of 1:1 red cell suspensions. Measured differences in sample heating rates and temperature gradients between microwave-exposed and heated control suspensions may account in part for the differential effect of microwave exposure but such effects do not appear to explain the results of this study fully.     

Investigation of the effects of continuous-wave,pulse- and amplitude-modulated microwaves on single excitable cells of chara corallina

Single internodal excitable cells of Chara corallina were exposed to CW, pulse-modulated and sinusoidally modulated S-band microwave fields in a temperature-controled waveguide exposure chamber. All electrical measurements were made external to the waveguide (ie, under no impressed microwave field). The dependent variables measured before, during, and after exposure to the S-band microwave fields included: resting potential, amplitude of the action potential, rise and decay time of the action potential, conduction velocity, and excitability. Cells maintained at 22 ± 0.1 °C during exposure showed no consistent or statistically significant microwave-dependent alterations in any of the dependent variables.     

Deletion and Complementation Analysis of the Biotin Gene Cluster of Escherichia coli

Genetic deletions that terminate within the cluster of genes needed for biotin biosynthesis in Escherichia coli have been isolated and mapped by transduction with phages lambda and P1. These deletions order the point mutations in each of the five genes. Mutations causing biotin dependence were incorporated into lambdapbio transducing phages. New bio(-) mutations were induced by exposure of lambdapbio particles to ultraviolet light. Tests of complementation between such bio(-)pbio particles and bio(-) mutant cells divide the bio(-) mutations into five cistrons: bioA, bioB, bioF, bioC, and bioD. Certain bioA and bioF mutations exhibit intragenic complementation, suggesting that these genes determine enzymes composed of identical subunits.