Biomedical subjects

A A Brayman

Publications and source records attributed to A A Brayman.

41 records · Page 3Linked to original sources

PubMed1986

Induction of ELF transmembrane potentials in relation to power-frequency electric field bioeffects in a plant root model system. II. The effect of 60 Hz electric fields on the growth of different regions of the cucurbit root elongation zone.

The region of elongation in Cucumis sativus and Cucurbita maxima roots was marked at increasing distances from the apex to provide an analog of increasing cell size. These roots were exposed/sham-exposed to 60 Hz electric fields and the growth rates of the root segments measured. The growth rate effect magnitude varied with increasing distance from the root tip at constant field strength, and with increasing applied field strength. These results provide strong, qualitative support for the postulate that ELF transmembrane potential induction is involved in the stimulation of ELF electric field effects in the plant root model system.

Cell Division↗

PubMed1986

Ribulose-1,5-bisphosphate carboxylase activity of Populus tremuloides Michx. bark tissues.

Ribulose-1,5-bisphosphate (RubP) carboxylase was isolated from bark tissue of Populus tremuloides Michx. by a one-step Sephadex G l00-120 column chromatography procedure. The peak fraction had specific activity of 1.3 micromol CO(2) mg(-1) chlorophyll min(-1). The bark RubP carboxylase activity was comparable to that of leaf tissues. Thus, young corticular tissues are photosynthetically competent and contain sufficient RubP carboxylase to account for the reported rates of photosynthesis.

Journal Article↗

PubMed1985

The relationship between sensitivity to 60-Hz electric fields and induced transmembrane potentials in plants root cells.

Growth rates and cell diameters were determined from 12 species of plant roots exposed to a 60-Hertz (Hz) electric field of 360 Volts per meter (V/m) in an aqueous inorganic nutrient medium [conductivity: 0.07-0.09 Siemens per meter (S/m)]. The degree of growth depression ranged from zero to nearly 100 percent of control. Cell diameters ranged from 13.5 to 31.8 micron as an averaged value for procambial, cortical, and meristem cells. Sensitivity to the electric field as determined by root growth rate reduction increased with increasing cell size. Sensitivity also increased with increase in 60 Hz induced transmembrane potentials; the transmembrane potential threshold for growth reduction was about 6.0 mV and the potential for near-complete cessation of growth was about 10-11 mV. Two different hypothetical mechanisms of action by which applied electric fields induce biological effects at the cellular level were tested. The two mechanisms pertain to different possible modes of action of applied electric fields: one mechanism postulates the involvement of the transmembrane field, the other mechanism postulates the tangential electric field as the important factor for inducing biological effects. The data support the transmembrane and not the tangential field mechanism. It is concluded that the effects observed are consistent with a membrane related mechanism and that there is a narrow range (a few mV) between threshold and debilitating induced membrane potentials.

Electromagnetic Fields↗

PubMed1982

Photosynthesis and Respiration of Developing Populus tremuloides Internodes.

The photosynthetic and respiratory performance of developing internodes of Populus tremuloides was evaluated by infrared gas analysis. Anatomical and morphological transitions were related to metabolic activity. Photosynthetic rates ranged from 6.0 to 10.0 milligrams CO(2) per decimeter squared per hour in the youngest internodes to 2.5 to 3.8 milligrams CO(2) per decimeter squared per hour in internodes with fully developed bark tissues. Respiration exceeded the rate of photosynthesis on the average by a factor of two. Stem photosynthesis increased with temperature up to 40 degrees C and declined steeply between 40 and 50 degrees C. Stem respiration increased nearly linearly to temperatures as high as 50 degrees C.

Journal Article↗

PubMedDate not supplied

Hyperthermic teratogenicity, thermal dose and diagnostic ultrasound during pregnancy: implications of new standards on tissue heating.

Hyperthermia is a recognized teratogen in mammalian laboratory animals and is a suspected teratogen for humans. The purpose of this synopsis is to reanalyse existing data on hyperthermia-induced teratogenic effects in experimental mammalian systems in terms of a thermal dose (temperature:time) concept, and then to illustrate the utility of this concept to human situations involving potential thermal increments to post-implantation embryos and foetuses. For example, the threshold temperature elevation for hyperthermia-induced teratogenic effects in experimental mammals is estimated (but not rigorously tested) to be approximately 1.5 degrees C above core values for exposures of long duration, possibly with a thermal dose of approximately 5 min duration or more at 4 degrees C. This level of tissue temperature increment is within the capability of some modern diagnostic ultrasound (DUS) devices sold within the USA and abroad. Epidemiological studies have not indicated any hazard from the use of DUS, but such studies are limited in sensitivity and were conducted with DUS devices whose acoustic outputs were relatively low compared to those presently available. After a regulatory change that allowed for substantially increased acoustic outputs, modern DUS devices were mandated to provide the user with on-screen information (the Thermal Index, or 'TI') about ultrasound-induced temperature increments in the target tissue. The TI is generally accurate to within a factor of 2, but the factor may be as high as 6 in certain obstetric settings. Thus, informed use of and attention to the TI is strongly advised, with this admonition gaining increased emphasis if the present regulations regarding allowable acoustic outputs of DUS devices were to be further relaxed or eliminated.

Animals↗