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Biomedical subjects

W F Pickard

Publications and source records attributed to W F Pickard.

At least 37 records · Page 2Linked to original sources
PubMed1997

Measurement of DNA damage after exposure to electromagnetic radiation in the cellular phone communication frequency band (835.62 and 847.74 MHz).

Mouse C3H 10T1/2 fibroblasts and human glioblastoma U87MG cells were exposed to cellular phone communication frequency radiations to investigate whether such exposure produces DNA damage in in vitro cultures. Two types of frequency modulations were studied: frequency-modulated continuous-wave (FMCW), with a carrier frequency of 835.62 MHz, and code-division multiple-access (CDMA) centered on 847.74 MHz. Exponentially growing (U87MG and C3H 10T1/2 cells) and plateau-phase (C3H 10T1/2 cells) cultures were exposed to either FMCW or CDMA radiation for varying periods up to 24 h in specially designed radial transmission lines (RTLs) that provided relatively uniform exposure with a specific absorption rate (SAR) of 0.6 W/kg. Temperatures in the RTLs were monitored continuously and maintained at 37 +/- 0.3 degrees C. Sham exposure of cultures in an RTL (negative control) and 137Cs gamma-irradiated samples (positive control) were included with every experiment. The alkaline comet assay as described by Olive et al. (Exp. Cell Res. 198, 259-269, 1992) was used to measure DNA damage. No significant differences were observed between the test group exposed to FMCW or CDMA radiation and the sham-treated negative controls. Our results indicate that exposure of cultured mammalian cells to cellular phone communication frequencies under these conditions at an SAR of 0.6 W/kg does not cause DNA damage as measured by the alkaline comet assay.

Animals↗
PubMed1995

Trivial influences: a doubly stochastic Poisson process model permits the detection of arbitrarily small electromagnetic signals.

If a weak, exogenous, extremely low-frequency (ELF) electric or magnetic field is to produce biological sequelae, then there must exist averaging sufficient to lift some primary effect of that field above the endogenous stochastic variations of the biological system. One way in which a field could accomplish this is by changing the intensity of some stochastic operation that controls an important and not trivially reversible biological transformation. In this paper, this operation is modeled as a doubly stochastic Poisson process. It is then shown, first, that (in theory) even a minuscule exogenous influence might appreciably shift the incidence of a sufficiently rare transformation and, second, that this shift might be observable if a trial were allowed to run long enough over a sufficiently large population of exposed entities.

Algorithms↗
PubMed1986

A theory of the saturable ohmic channel.

Let the passage of type-lambda ions through a type-sigma channel be determined only by the ionic valence z lambda, by the thermal energy kT, by the ion concentrations on the out- and in- sides [S lambda]o and [S lambda]i, by the inside with-respect-to outside voltage of the channel E, by a single descriptor of channel saturation [S sigma lambda], and by a single descriptor (permeance) the ease of channel transit P sigma lambda. Then, if the channel current i sigma lambda, due to lambda-ions is ohmic about the Nernst potential, is a function of the sum ([S lambda]o + [S lambda]i) and not of [S lambda]o or [S lambda]i independently, and saturates in a Michaelis-Menten fashion, it follows that (Formula: see text) where F is the Faraday constant.

Biological Transport↗
PubMed1985

Low-power 2.45-GHz microwave radiation affects neither the vacuolar potential nor the low frequency excess noise in single cells of characean algae.

Single, giant cells of the eukaryotic green algae Chara braunii and Nitella flexilis were subjected to short-, intermediate-, and long-term irradiations with 2.45-GHz microwaves. A search was carried out for radiation-correlated shifts (i) in both the dc level and the rms low-frequency excess noise of the vacuolar potential and (ii) in the membrane resistivity. No reliable shifts were observed, either in normal cells or in cells subjected to reduced temperatures or the poison ethacrynic acid.

Chlorophyta↗
PubMed1985

Extremely low frequency resistance fluctuations of chara membrane.

The membrane resistivity of resting characean cells was measured and found to fluctuate unpredictably about its resting level. The amplitude of these fluctuations relative to the mean resistivity was normally somewhat larger than the same ratio for the vacuolar voltage; further the resistivity and voltage fluctuations seemed not to be strongly correlated.

Journal Article↗
PubMed1984

Offset of the vacuolar potential of Characean cells in response to electromagnetic radiation over the range 250 Hz-250 kHz.

Measurements were made of the small, transient offsets of vacuolar potential produced in single cells of Nitella flexilis and Chara braunii by isolated bursts of audio frequency electromagnetic radiation. The offsets increased in magnitude with decreasing frequency of the electromagnetic radiation and, below about 6 kHz, seemed to approach a low-frequency asymptote. This frequency dependence for the offset is shown to be in accordance with a previously developed model in which the incident radiation is weakly rectified by the cell's membrane system.

Animals↗
PubMed1984

The membrane potential of characean cells exposed to amplitude-modulated, low-power 147-MHz radiation.

The membrane potential of isolated cells of Chara braunii or Nitella flexilis was monitored while the cells were exposed, at nominal power densities from 2 to 1,000 W/m2, to 147-MHz radiation amplitude modulated at frequencies from 4 to 64 Hz. Phase-sensitive detection was used to seek radiation-correlated changes in the membrane potential, and none were apparent under any of the conditions used in this investigation.

Electromagnetic Phenomena↗
PubMed1984

Vacuolar hyperpolarizing offsets in characean cells exposed to mono- and bichromatic CW and to squarewave-modulated electromagnetic radiation in the band 200-1,000 MHz.

Single giant cells of the algae Chara braunii and Nitella flexilis were exposed to bursts of electromagnetic radiation (monochromatic CW, bichromatic CW, or squarewave-modulated) in the band 200-1,000 MHz while their vacuolar potentials were monitored using micropipettes. The slow hyperpolarizing response that was observed seemed to be linear in the power deposited in the vicinity of the cell, to be otherwise indifferent to irradiation frequency or modulation, and therefore to be thermal in origin.

Electromagnetic Phenomena↗
PubMed1984

Nonlinear equivalent circuits for membranes.

The problem of obtaining Helmholtz equivalents for nonlinear resistive one-ports is considered. Two fundamentally different classes of equivalent are described, one local and the other global. For each, necessary and sufficient conditions are derived for the existence and uniqueness of either the Thévenin equivalent or the Norton equivalent or both. These concepts are illustrated (i) by proving that a cell whose channels and pumps are monotone in the membrane potential will, in the absence of net state changes in these ionophores, possess a unique stable resting potential and (ii) by demonstrating that it is in principle impossible to assign unique equivalent circuits to such ionophores.

Cell Membrane↗
PubMed1982

Effects of electromagnetic radiation in the range 20-300 MHz on the vacuolar potential of characean cells.

A giant cell (circa 10 mm long) of Chara braunii or Nitella flexilis was placed in a microstrip exposure apparatus, and the vacuolar potential at one end was monitored with a micropipette while the other end was exposed to pulses of VHF radiation at electric field strengths up to 6250 V/m. With suitable filtering and signal averaging, offsets of the vacuolar potential could be detected in real time and at levels as low as 1 microV. The only effect that has been reproducibly observed in the carrier frequency range 20-300 MHz was the slow ramp-like hyperpolarization previously reported [Pickard and Barsoum, 1981] and tentatively attributed to electromagnetic heating of the system. The slopes of these ramps became more pronounced with increasing frequency and behaved in accordance with theoretical predictions.

Chlorophyta↗
PubMed1982

The vacuolar potential of Characean cells subjected to electromagnetic radiation in the range 200-8,200 MHz.

Single giant cells of Chara braunii and Nitella flexilis were placed in a microstrip exposure apparatus and subjected to bursts of electromagnetic radiation (carrier frequencies from 200 to 8,200 MHz) at a nominal power level of 100 W/m2. The vacuolar potential was monitored with a micropipette, and offsets as low as 1 microV could be resolved in real time by suitable filtering and signal averaging; under these conditions, no offsets of the vacuolar potential were detected. At much higher power levels (corresponding to greater than or equal to 2 V rms between microstrip and ground plane), the slow hyperpolarizing ramp reported at lower frequencies could be seen but, because of insufficient power, could not be accurately measured. It appeared to decay beyond 500 MHz and to be absent at and above 950 MHz. To investigate reports that snail neurons irradiated for 1 h at 2,450 MHz and approximately 15.5 W/kg developed lowered membrane resistivities, Characean cells were exposed in the microstrip apparatus for 1 h at 2,450 MHz and 230 W/m2; their membrane resistivities were found to be lowered about 18.5%.

Chlorophyta↗
PubMed1982

Why is the substomatal chamber as large as it is?

The rate of CO(2) uptake by the mesophyll is examined as a function of the size of the substomatal chamber. Using the techniques of classical electric circuit analysis and a model in which the uptake is linear in the ambient CO(2) concentration, it is shown that the optimal chamber radius is several times larger than is the pore radius. This is somewhat larger than necessary for the reduction of transpirational water loss, and it offers an explanation for the otherwise inexplicably large size of the chamber.

Journal Article↗
PubMed1979

Measurement of phospholipid monolayer surface potentials at a hydrocarbon-electrolyte interface.

The phospholipid monolayer spread at a hydrocarbon-electrolyte interface can be used as a model system for the plasma membrane and its properties and structure probed by measurements of surface pressure and surface potential. To facilitate such studies, (i) the theory of the vibrating plate (Kelvin) method of measuring surface potentials is reëxamined and a new interpretation given for the potentials measured and (ii) a new apparatus for performing these measurements is described. The theory and apparatus are illustrated by measurements on films of distearoyl phosphatidylcholine at the interface between 2,2,4-trimethylpentane (isooctane) and 0.1 M NaCl.

Cell Membrane↗
PubMed1979

Phospholipid monolayers at the hydrocarbon-electrolyte interface. The interrelation of film potential and film pressure.

Measurements of surface pressure of surface potential are reported for films of distearoyl phosphatidylcholine (density range: 0.15--2.65 . 10(18) molecules/m2) spread at the interface between 2,2,4-trimethylpentane and 100 mM NaCl. Low density behavior of the surface pressure is explained using classical viral theory. The behavior of the surface potential is qualitatively explained for all densities in terms of the dipole moments associated with the carboxyl groups and headgroups of the phosphatidylcholine.

Electrolytes↗
PubMed1976

The insensitivity of frog heart rate to pulse modulated microwave energy.

Frey and Seifert (1968) have reported that pulse modulated microwave irradiation of low average energy density can produce tachycardia in isolated frog hearts. In an effort to examine this phenomenon, two types of experiments were carried out: 1. frog hearts were irradiated in situ with 100 mus bursts of microwave energy at either 10.0 GHz or 1.42 GHz; 2. isolated frog hearts were irradiated with 100 mus bursts of microwave energy at 1.42 GHz. No significant changes in heart rate were observed.

Animals↗