Radio-frequency bioeffects at the membrane level: Separation of thermal and athermal contributions in the characeae

Pickard, William F.; Barsoum, Yousri H.

doi:10.1007/bf01870751

Cited by 35 publications

(27 citation statements)

References 25 publications

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“…No athermal effect similar to that found below 20 MHz [Pickard and Barsoum, 1981; Barsoum and Pickard, 19821 was ever detected between 20 and 300 MHz.…”

Section: General Observationsmentioning

confidence: 62%

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

Barsoum

Pickard

1982

Bioelectromagnetics

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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.

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“…No athermal effect similar to that found below 20 MHz [Pickard and Barsoum, 1981; Barsoum and Pickard, 19821 was ever detected between 20 and 300 MHz.…”

Section: General Observationsmentioning

confidence: 62%

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

Barsoum

Pickard

1982

Bioelectromagnetics

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“…This now brings to five the number of electrophysiological measures which can be obtained from a characean cell without current or voltage clamping it: VO, Ro, 6 V, 6R, and radio-frequency rectification offset (5). Each presumably offers a different viewpoint upon the underlying behaviors of the channels and pumps.…”

Section: Discussionmentioning

confidence: 99%

“…During an experiment, a cell was maintained in a flow-through holder (5) Figure 1. These data are typical in that (a) there is no obvious algorithm for predicting one trace from the other and (b) the fluctuations of 6R relative to Ro tend to be significantly larger than the fluctuations of 6 V relative to V0.…”

Section: Methodsmentioning

confidence: 99%

Extremely Low Frequency Resistance Fluctuations of Chara Membrane

Gokhale

Pickard²

1985

Plant Physiol.

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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.It is well known that stochastic fluctuations of membrane current and transmembrane voltage are normally present in cells (1); and, in particular, fluctuations of the vacuolar voltage of characean cells have been studied extensively (2-4, 7, 8). Such fluctuations, reflecting as they do changes in the ion transporting elements (ionophores) ofthe cell membrane, are presumably also accompanied by fluctuations of membrane resistance (or, equivalently, conductance). However, while the presumed existence of resistance fluctuations has been remarked upon (1, 9), a detailed theory oftheir relation to voltage fluctuations seems not to have been worked out, and we are aware of no instance in which they have been measured. MATERIALS AND METHODSPlant Material. Chara braunii (Gm.) was collected locally and maintained in tanks in a laboratory window with supplemental fluorescent illumination. On the day before use, internodal cells roughly 8 x 0.25 mm were excised and equilibrated overnight in the standard bathing solution employed during the experiment.2.5 mM KCI, 2.5 mM NaCl, 0.5 mM CaCl2, 0.5 mM MgC92, 0.5 mM Hepes, 0.25 mm NaOH; its pH was near 7.3.Experimental Arrangement. During an experiment, a cell was maintained in a flow-through holder (5) and impaled for resistance measurements by two pipettes filled with 2.75 M KCI in 2%(w/v) agar (7). Temperature was maintained near 15°C by a feedback-controlled thermoelectric cooling system (7) operated in an overdamped mode so that oscillation of the drive voltage for the cooler was negligible. Illumination came principally from a low voltage microscope light operated from a regulated dc power supply. Thus, obvious variations of the ambient conditions did not underlie the observed variations 6R and 6 V of, respectively, the membrane resistivity and vacuolar potential from their average values Ro and V0.Electronics. Two-pipette measurement of local resistance is standard (7) and here was implemented by measuring the offset 1 Supported in part by National Science Foundation grant ECS-8105485 and Office ofNaval Research contracts N000 14-82-K-0261 and N000 14-84-K-0457. of vacuolar voltage produced by injecting a balanced squarewave of current of approximately 4 Hz and a magnitude sufficient to offset the vacuolar voltage by about 250 uV peak to peak. To emphasize fluctuations of resistance, the vacuolar voltage was (a) high pass filtered at 0.2 Hz to remove the resting potential, (b) rms -+ dc converted, (c) low pass filtered at 30 mHz, (d) dc offset to yield a signal which varied stochastically about a mean level of approximately zero, (e) amplified, and (f) captured by a chart recorder. This then produced a record of an...

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“…Electrogenic transport in plant cells has so far been investigated primarily by studying either the resting potentials and membrane resistivities of the cells or their rates of uptake of radioisotopes and by noting how these observables vary as the cells are challenged by various inhibitors or by various bathing media or by altered light intensities (el Spanswick, 1972;Poole, 1978). In particular, the only aspect of the resting potential commonly examined is its DC level although its low frequency power spectral density function (e.g., Roa & Pickard, 1976a;Ferrier, Morvan, Lucas & Dainty, 1979) or its response to pulsed radio-frequency irradiation (Pickard & Barsoum, 1981) are known to contain significant additional information.…”

Section: Introductionmentioning

confidence: 99%

Radio-frequency rectification in electrogenic and nonelectrogenic cells ofChara andNitella

Barsoum

Pickard

1982

J. Membrain Biol.

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Summary. Electrogenic cells of Chara braunii and Nitella flexiliswere placed in a pulse-modulated radio-frequency electric field of up to 6000 V/re. Their vacuolar resting potentials were found to experience submillivolt depolarizing offsets (typically 140 ~tV at 250 kHz) which were relatively independent of temperature, increased linearly with resting potential from a zero near -210 mV, and had a cutoff (putatively due to ion transit times) near 5 MHz.By contrast, nonelectrogenic cells experienced hyperpolarizing offsets (typically 1100 gV at 250 kHz) which increased in magnitude with increasing temperature, were independent of resting potentiaI, and had a transit time cutoff near 10 MHz.The ionic mobilities inferred from these cutoff frequencies are somewhat higher than would be expected for active transport and presumably reflect passive conductance mechanisms which therefore must be presumed different for the electrogenic and nonelectrogenic states.Key words Characeae . electrogenesis 9 ion flux 9 radio-frequency bioeffects 9 rectification . transit time . fusicoccin

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Radio-frequency bioeffects at the membrane level: Separation of thermal and athermal contributions in the characeae

Cited by 35 publications

References 25 publications

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

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

Extremely Low Frequency Resistance Fluctuations of Chara Membrane

Radio-frequency rectification in electrogenic and nonelectrogenic cells ofChara andNitella

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